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Publication numberUS20020053353 A1
Publication typeApplication
Application numberUS 09/805,747
Publication dateMay 9, 2002
Filing dateMar 13, 2001
Priority dateMar 13, 2000
Publication number09805747, 805747, US 2002/0053353 A1, US 2002/053353 A1, US 20020053353 A1, US 20020053353A1, US 2002053353 A1, US 2002053353A1, US-A1-20020053353, US-A1-2002053353, US2002/0053353A1, US2002/053353A1, US20020053353 A1, US20020053353A1, US2002053353 A1, US2002053353A1
InventorsShintaro Kawata, Masashi Okada, Sumito Shimizu
Original AssigneeShintaro Kawata, Masashi Okada, Sumito Shimizu
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Methods and apparatus for cleaning an object using an electron beam, and device-fabrication apparatus comprising same
US 20020053353 A1
Abstract
Apparatus and methods are disclosed for cleaning an object, such as a reticle or electron-optical component used in performing electron-beam microlithography, using an electron beam. The cleaning can be performed in the presence or absence of a treatment gas. When performed without a treatment gas, an electron beam is directed to impinge on the object at an energy sufficient to volatilize contaminant deposits on the object. When performed with a treatment gas, the electron beam need not be directed at the object, but electrons from the beam have an energy sufficient to ionize molecules of the treatment gas. The ionized molecules volatilize the contaminant deposits for removal using a vacuum pump. For example, the beam can be directed to a scattering body that produces scattered electrons having sufficient energy to volatilize the contaminant deposits.
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Claims(41)
What is claimed is:
1. A contamination-removal device, comprising:
a treatment chamber defining an interior space in which an object, having a deposit of a contaminant substance and requiring cleaning to remove the deposit, can be situated;
a chamber-evacuation pump in communication with the treatment chamber, the chamber-evacuation device being configured to evacuate the interior space of the treatment chamber;
a gas-inlet in communication with the treatment chamber, the gas-inlet being configured to introduce a treatment gas into the interior space of the treatment chamber; and
an electron-beam irradiator situated and configured to irradiate an electron beam in the interior space of the treatment chamber such that the electron beam ionizes molecules of the treatment gas, and the ionized molecules of the treatment gas react with molecules of the contaminant substance on the object to volatilize the contaminant substance from the object.
2. The contamination-removal device of claim 1, wherein the treatment gas comprises at least one gas selected from a group consisting of water vapor, oxygen, ozone, and oxygen radicals.
3. The contamination-removal device of claim 1, further comprising a lens column and a wafer chamber, wherein the wafer chamber comprises the treatment chamber.
4. The contamination-removal device of claim 1, wherein the lens column contains the electron-beam irradiator.
5. The contamination-removal device of claim 4, further comprising an electron-optical system for illuminating the reticle with an electron beam.
6. The contamination-removal device of claim 5, wherein:
the electron-optical system comprises the electron-beam irradiator; and
the electron-optical system is situated within the lens column.
7. The contamination-removal device of claim 3, further comprising a scattering body situated within either the lens column or the wafer chamber so as to be bombarded with incident electrons from the electron-beam irradiator and form scattered electrons.
8. A microelectronic-device fabrication apparatus, comprising the contamination-removal device of claim 1.
9. An electron-beam microlithography apparatus, comprising:
a lens column containing an electron-optical system configured to illuminate a reticle with an electron beam;
a wafer chamber defining an interior space configured to enclose a substrate to be exposed with a pattern defined on the reticle and transferred to the substrate by the electron beam propagating from the reticle to the substrate;
at least one vacuum pump in communication with the lens column and wafer chamber, the vacuum pump being configured to evacuate the interior spaces of the lens column and wafer chamber;
a gas-inlet in communication with the wafer chamber, the gas-inlet being configured to introduce a treatment gas into the interior space of the wafer chamber; and
the wafer chamber being configured to contain a scattering body situated so as to be irradiated by the electron beam from the electron-optical system, the electron beam irradiating the scattering body causing the scattering body to produce scattered electrons that propagate to any of various locations in the wafer chamber and lens column to impinge on contaminant deposits at the various locations and to ionize molecules of the treatment gas introduced into the interior space, the ionized molecules reacting with and volatilizing the contaminant deposits.
10. The apparatus of claim 9, further comprising an electron-beam source situated in the lens column.
11. The apparatus of claim 9, wherein the treatment gas is at least one gas selected from a group consisting of water vapor, oxygen, ozone, and oxygen radicals.
12. An electron-beam microlithography apparatus, comprising:
an electron-beam source;
a process chamber defining an interior space;
an electron-optical system situated in the process chamber relative to the electron-beam source and configured to direct an electron beam from the source to a substrate situated downstream of the source;
a wafer stage situated in the process chamber, the wafer stage being configured to hold the substrate as the substrate is being irradiated by the electron beam;
a treatment-gas source connected to and configured to introduce a treatment gas into the process chamber; and
an electron-scattering body situated in the process chamber, the electron-scattering body being positionable so as to be irradiated by the electron beam and produce, from such irradiation, scattered electrons that propagate to any of various locations in the process chamber to impinge on contaminant deposits at the various locations and to ionize molecules of the treatment gas introduced into the interior space, the ionized molecules reacting with and volatilizing the contaminant deposits.
13. An electron-beam microlithography apparatus, comprising:
a process chamber defining an interior space;
an electron-optical system situated in the process chamber and comprising an electron-beam source, the electron-optical system being configured to irradiate a surface of a substrate selectively with an electron beam from the source;
a treatment-gas source connected to and configured to introduce a treatment gas into the process chamber; and
an electron-beam irradiation device situated in the process chamber separately from the electron-optical system, the electron-beam irradiation device being configured to produce a respective electron beam that impinges on the treatment gas in the process chamber so as to ionize molecules of the treatment gas, the ionized molecules being available to react with and volatilize a contaminant deposit in the process chamber.
14. The apparatus of claim 13, wherein the treatment gas is at least one gas selected from a group consisting of water vapor, oxygen, ozone, and oxygen radicals.
15. A method for removing a deposit of a contaminant in a process chamber of an apparatus that employs an electron beam to achieve a desired result, the method comprising the steps:
providing a treatment gas comprising molecules that become ionized when irradiated by electrons;
introducing molecules of the treatment gas into the process chamber;
when the process chamber contains molecules of the treatment gas, irradiating the molecules of the treatment gas in the process chamber with the electron beam to ionize the molecules of the treatment gas;
allowing the ionized molecules of the treatment gas to react with and volatilize the deposit; and
removing the volatilized deposit from the process chamber.
16. The method of claim 15, wherein the step of removing the volatilized deposit from the process chamber comprises evacuating the process chamber.
17. The method of claim 15, wherein the treatment gas is at least one gas selected from a group consisting of water vapor, oxygen, ozone, and oxygen radicals.
18. A method for removing a deposit of a contaminant in a process chamber of an apparatus that employs an electron beam to achieve a desired result, the method comprising the steps:
providing a treatment gas comprising molecules that become ionized when irradiated by electrons;
introducing molecules of the treatment gas into the process chamber;
placing an electron-scattering body in the process chamber such that the electron beam can impinge on the electron-scattering body and thus cause the electron-scattering body to produce scattered electrons;
when the process chamber contains molecules of the treatment gas, irradiating the electron-scattering body with the electron beam to produce scattered electrons that ionize the molecules of the treatment gas; and
allowing the ionized molecules of the treatment gas to react with and volatilize the deposit.
19. The method of claim 18, wherein the treatment gas is at least one gas selected from a group consisting of water vapor, oxygen, ozone, and oxygen radicals.
20. A method for removing a deposit of a contaminant in a process chamber, comprising the steps:
providing a treatment gas comprising molecules that become ionized when irradiated by electrons;
introducing molecules of the treatment gas into the process chamber;
providing in the process chamber an electron-beam irradiation device configured to produce an electron beam;
placing an electron-scattering body in the process chamber such that the electron beam can impinge on the electron-scattering body and thus cause the electron-scattering body to produce scattered electrons;
when the process chamber contains molecules of the treatment gas, irradiating the electron-scattering body with the electron beam to produce scattered electrons that ionize the molecules of the treatment gas; and
allowing the ionized molecules of the treatment gas to react with and volatilize the deposit.
21. The method of claim 20, wherein the treatment gas is at least one gas selected from a group consisting of water vapor, oxygen, ozone, and oxygen radicals.
22. A method for cleaning a reticle in a process chamber of an electron-beam microlithography apparatus used to transfer an image of a pattern, defined by the reticle, onto a resist-coated surface of a substrate, the method comprising the steps:
(a) placing the reticle in an interior space defined by the process chamber;
(b) applying a subatmospheric pressure to the interior space; and
(c) directing an electron beam to impinge on the reticle in the process chamber, while deflecting electrons of the beam passing through the reticle away from the resist-coated surface so as not to expose the resist.
23. The method of claim 22, wherein, in step (c), the electron beam impinging on the reticle has an energy sufficient to volatilize a deposit of a contaminant on the reticle as the reticle is being irradiated with the electron beam.
24. The method of claim 23, wherein the energy of the electron beam used to clean the reticle is greater than an energy of the electron beam used to expose the resist-coated surface of the substrate with the reticle pattern.
25. The method of claim 22, wherein, in step (c), the electron beam impinging on the reticle has an energy sufficient to confer a negative charge to a deposit of a contaminant on the reticle and to cause the deposit to detach from the surface of the reticle.
26. The method of claim 25, further comprising the steps of:
providing a dust collector in the process chamber;
providing the dust collector with a positive charge sufficient to attract the detached deposit; and
collecting the detached deposit using the dust collector.
27. A method for performing microlithography of a pattern, defined on a reticle, onto a resist-coated surface of a substrate, the method comprising:
(a) placing the reticle and substrate in the process chamber, the reticle being situated so as to be irradiated with an upstream electron beam and to produce a downstream electron beam carrying an image of an irradiated region of the reticle, and the substrate being situated such that the resist-coated surface can be exposed with the image carried by the downstream electron beam;
(b) evacuating the process chamber to produce a subatmospheric pressure in the process chamber;
(c) in a reticle-cleaning mode of operation, directing the upstream electron beam to impinge on the reticle while directing the downstream electron beam away from the resist-coated surface so as to avoid exposing the resist; and
(d) in a substrate-exposure mode of operation, directing the upstream electron beam to irradiate a region on the reticle while directing the downstream electron beam to a corresponding location on the resist-coated surface of the substrate so as to transfer the pattern from the reticle to the substrate.
28. The method of claim 27, wherein:
in step (c), the electron beam has a first energy sufficient to volatilize a deposit of a contaminant on the reticle;
in step (d), the electron beam has a second energy sufficient to expose the resist; and
the first energy is greater than the second energy.
29. The method of claim 27, further comprising the steps of:
providing a dust collector in the process chamber; and
during step (c), providing the dust collector with a positive charge.
30. The method of claim 29, wherein, in step (c):
the electron beam impinging on the reticle has an energy sufficient to confer a negative charge to a deposit of a contaminant on the reticle and to detach the deposit from the reticle; and
the detached deposit is attracted to and collected by the dust collector.
31. An electron-beam microlithography apparatus operable to project an image of a pattern, defined by a reticle, onto a resist-coated surface of a substrate, the apparatus comprising:
a process chamber defining an interior space;
a vacuum pump, in communication with the interior space, configured to produce a subatmospheric pressure in the interior space;
an electron-beam source situated within the interior space and configured to produce an electron beam propagating downstream of the source;
a deflector situated within the interior space and configured, when electrically energized, to deflect the electron beam propagating from the source; and
a main controller connected to the electron-beam source and to the deflector, the main controller being configured to operate in first and second operational modes, wherein in the first operational mode the electron beam from the source irradiates the reticle, and electrons of the beam passing through the reticle are deflected by the deflector away from the resist-coated surface so as not to expose the resist, and in the second operational mode the electron beam from the source irradiates a region of the reticle, and electrons of the beam passing through the reticle are deflected by the deflector to a corresponding region on the resist-coated surface so as to imprint the resist-coated surface with the pattern.
32. The apparatus of claim 31, wherein, in the first operational mode, the main controller causes the source to produce the electron beam having a higher intensity than in the second operational mode, the higher intensity in the first operational mode being sufficient to volatilize a deposit of a contaminant on the reticle.
33. The apparatus of claim 31, further comprising a dust collector situated in the process chamber and connected to the main controller, wherein in the first operational mode the electron beam has an energy sufficient to confer a negative charge to a deposit of a contaminant on the reticle and to detach the deposit from the reticle, and the main controller applies a positive charge to the dust collector, the positive charge being sufficient to attract the detached negatively charged deposit of the contaminant.
34. A method for cleaning a reticle for use in performing charged-particle-beam (CPB) microlithography, comprising the steps:
(a) placing the reticle in a process chamber in which CPB microlithography of the reticle is performed;
(b) directing an ion beam or electron beam to irradiate a contaminant deposit on the reticle; and
(c) while performing step (b), introducing molecules of a reactive gas to an area where the ion beam is irradiating the deposit, wherein the irradiating beam ionizes the molecules of reactive gas that then react with and volatilize the contaminant deposit.
35. The method of claim 34, wherein the reactive gas comprises a first gas selected from a group consisting of gaseous fluoride compounds, gaseous chloride compounds, and gaseous bromide compounds.
36. The method of claim 35, wherein the reactive gas comprises a second gas selected from a group consisting of an inert gas, nitrogen gas, and oxygen gas.
37. A charged-particle-beam (CPB) microlithography apparatus, comprising:
an illumination-optical system situated and configured to illuminate a reticle, defining a pattern to be transferred to a substrate, with a charged-particle illumination beam;
a reticle stage situated and configured to movably hold the reticle as the reticle is being illuminated by the illumination beam, so as to produced a patterned imaging beam propagating downstream of the reticle;
a projection-optical system situated and configured to direct and image the imaging beam on a sensitive substrate;
a substrate stage situated and configured to movably hold the sensitive substrate as the sensitive substrate is being exposed with the imaging beam;
an ion-beam source and ion-beam optical system situated and configured to irradiate a focused ion beam onto a predetermined location on the reticle; and
a process chamber enclosing the illumination-optical system, the reticle stage, the projection-optical system, the substrate stage, the ion-beam source, and the ion-beam optical system.
38. A charged-particle-beam (CPB) microlithography apparatus, comprising:
an illumination-optical system situated and configured to illuminate a reticle, defining a pattern to be transferred to a substrate, with a charged-particle illumination beam;
a reticle stage situated and configured to movably hold the reticle as the reticle is being illuminated by the illumination beam, so as to produced a patterned imaging beam propagating downstream of the reticle;
a projection-optical system situated and configured to direct and image the imaging beam on a sensitive substrate;
a substrate stage situated and configured to movably hold the sensitive substrate as the sensitive substrate is being exposed with the imaging beam;
a probe-light source probe-light optical system situated and configured to irradiate a beam of probe light onto a surface of the reticle, the probe light being used to inspect the reticle for a contaminant deposit on the surface of the reticle;
a light detector for detecting a characteristic of the probe light as the probe light encounters a contaminant deposit on the reticle; and
a process chamber enclosing the illumination-optical system, the reticle stage, the projection-optical system, the substrate stage, the probe-light source, and the probe-light optical system.
39. The apparatus of claim 38, wherein the probe-light optical system is configured to direct the beam of probe light selectively on an upstream-facing surface of the reticle and on a side-wall of an aperture in the reticle.
40. The apparatus of claim 39, wherein the probe light is selected from the group consisting of UV light, deep UV light, and an electron beam.
41. A charged-particle-beam (CPB) microlithography apparatus, comprising:
an illumination-optical system situated and configured to illuminate a reticle, defining a pattern to be transferred to a substrate, with a charged-particle illumination beam;
a reticle stage situated and configured to movably hold the reticle as the reticle is being illuminated by the illumination beam, so as to produced a patterned imaging beam propagating downstream of the reticle;
a projection-optical system situated and configured to direct and image the imaging beam on a sensitive substrate;
a substrate stage situated and configured to movably hold the sensitive substrate as the sensitive substrate is being exposed with the imaging beam;
a probe-light source probe-light optical system situated and configured to irradiate a beam of probe light onto a surface of the reticle, the probe light being used to inspect the reticle for a contaminant deposit on the surface of the reticle;
a light detector for detecting a characteristic of the probe light as the probe light encounters a contaminant deposit on the reticle;
an ion-beam source and ion-beam optical system situated and configured to irradiate a focused ion beam onto a predetermined location on the reticle; and
a process chamber enclosing the illumination-optical system, the reticle stage, the projection-optical system, the substrate stage, the probe-light source, the probe-light optical system, the ion-beam source, and the ion-beam optical system.
Description
    FIELD OF THE INVENTION
  • [0001]
    This invention pertains to apparatus and methods for fabricating microelectronic devices such as integrated circuits, displays, and the like, especially such methods and apparatus in which the subject fabrication is performed in a “process chamber” (e.g., vacuum chamber). More specifically, the invention pertains to methods for removing contaminants adhering to a surface inside such a chamber, such as a surface of a reticle used in a charged-particle-beam microlithography apparatus. The invention also pertains to microelectronic-fabrication apparatus operable to perform removal of contaminants from a surface in a process chamber of the apparatus.
  • BACKGROUND OF THE INVENTION
  • [0002]
    Fabrication of microelectronic devices (e.g., semiconductor integrated circuits, displays, magnetic pickup heads, image sensors, micro-machines) involves a large number of process steps each performed using a specialized apparatus. Certain fabrication steps are performed multiple times during fabrication of a device. For example, microlithography is performed multiple times (sometimes a hundred times or more) in the fabrication of contemporary microprocessor chips and the like.
  • [0003]
    Continuing further with microlithography as a representative fabrication method, most microlithography still being performed is so-called “optical microlithography.” In optical microlithography, light (typically extreme UV light) is used as an energy beam with which a pattern, defined on a reticle, is transferred onto the surface of a resist-coated wafer or other substrate. In a related technique, termed “charged-particle-beam” (CPB) microlithography, the lithographic energy beam is a charged particle beam such as an electron beam or ion beam. Whereas optical microlithography need not be performed in a process chamber, CPB microlithography must be performed in a vacuum chamber.
  • [0004]
    A disadvantage with process chambers in general, especially vacuum chambers, is their tendency to accumulate deposits of contaminants. Example contaminants that can accumulate in a vacuum chamber of a CPB microlithography apparatus include precipitated gas or gas-reaction products, deposits of resist released from the wafer, and oil from the vacuum pump. Interaction of the deposits with the lithographic energy beam can produce deposits of hydrocarbons and other substances at various locations throughout the process chamber and on certain components inside the process chamber. Contaminant deposits also can form on a reticle or mask.
  • [0005]
    Especially in electron-beam microlithography apparatus and electron microscopes, irradiation of an electron beam over a long period of time can create conditions leading to increased rates of contaminant accumulation. Adhesion of contaminants to surfaces of electromagnetic lenses and the like can affect lens performance in an adverse manner. Adhesion of contaminants to a reticle can cause development of irregularities in the transmissivity of the reticle, which can result in deviations from specifications of the linewidths and profiles of projected patterns. This results in decreased accuracy of pattern transfer, and can result in production of devices that do not function to specifications. In addition, in an apparatus in which a charged particle beam is used, charging of contaminant deposits by the beam can generate extraneous electric fields that undesirably have unpredictable behavior and alter the beam trajectory, thereby causing decreased apparatus performance.
  • [0006]
    Current methods for removing contaminants from a surface (e.g., reticle, lens surface, or the like) in the process chamber typically involve removing the affected item from the process chamber and wet-cleaning the item. Wet-cleaning normally is performed using a solvent. This method requires substantial time in which to turn off the apparatus, open the process chamber, remove the affected item, clean the item, and replace it in the process chamber. Also, during cleaning, the apparatus is off and not performing useful work. This down-time adversely affects throughput of the fabrication process performed using the apparatus.
  • [0007]
    In an optical microlithography apparatus, a thin film known as a “pellicle” usually is applied to the surface of the reticle to prevent adhesion of particulate contamination directly to the reticle. The pellicle keeps the contaminant particles out of the conjugate plane of the projection lens, thereby preventing formation of images of the particles on the surface of the substrate. With a CPB microlithography apparatus, in contrast, a satisfactory material useful as a pellicle has not yet been found. Thin-film materials are available that are transmissive to a charged particle beam. However, passage of the beam through a thin film usually affects the beam in an adverse manner. Hence, available materials cannot be used to any substantial degree.
  • [0008]
    CPB microlithography apparatus that employ the so-called “cell-projection” approach generally utilize a small reticle that is not excessively expensive. A pellicle cannot be used with such a reticle. Nevertheless, the reticles are relatively inexpensive, so a contaminated reticle simply is discarded.
  • [0009]
    Other CPB microlithography approaches utilize reticles that are substantially larger than the reticles used in cell projection. These large reticles are very expensive; hence, it is not practical simply to discard contaminated reticles. The conventional solution to this problem is to suppress, as much as possible, contamination of the reticle and other surfaces inside the process chamber. Unfortunately, this approach frequently is not successful. For example, certain exposures are performed while scanning the reticle stage and wafer stage of the apparatus at high velocity during exposure of the pattern. Such motions of the wafer stage and reticle stage tend to generate fine particles. Also, fine particles can get into the process chambers from the outside environment during vacuum pump-down and venting. These problems cannot be avoided, and the introduced particles tend to adhere to the reticle as contaminants. As a result, reticle cleaning is indispensable for ensuring accurate transfer of the reticle pattern to the substrate surface. Again, reticle cleaning by conventional methods as summarized above undesirably reduces throughput.
  • SUMMARY OF THE INVENTION
  • [0010]
    In view of the shortcomings of conventional methods and apparatus as summarized above, an object of the invention is to provide methods and apparatus for removing contaminants adhering to the reticle or to any of various other components located in a “process chamber” of a process apparatus, without adversely affecting the throughput of the process apparatus. An exemplary process chamber is the vacuum chamber of an electron-beam microlithography apparatus.
  • [0011]
    To such end, and according to a first aspect of the invention, contamination-removal devices are provided. An embodiment of such a device comprises a treatment chamber, a chamber-evacuation pump, a gas-inlet, and an electron-beam irradiator. The treatment chamber defines an interior space in which an object, having a deposit of a contaminant substance and requiring cleaning to remove the deposit, can be situated. The chamber-evacuation pump is in communication with the treatment chamber, and is configured to evacuate the interior space. The gas-inlet is in communication with the treatment chamber, and is configured to introduce a treatment gas into the interior space. The electron-beam irradiator is situated and configured to irradiate an electron beam in the interior space such that the electron beam ionizes molecules of the treatment gas. The ionized molecules can react with molecules of the contaminant substance on the object so as to volatilize the contaminant substance from the deposit. The volatilized contaminant is removed using the chamber-evacuation pump.
  • [0012]
    The treatment gas desirably is one or more of: water vapor, oxygen, ozone, and oxygen radicals, which have high reactivity when ionized by an electron beam.
  • [0013]
    The treatment chamber can include a scattering body situated so as to be bombarded by the electron beam and form scattered electrons. The scattered electrons propagate to regions in the treatment chamber that otherwise would be difficult to reach using the electron beam directly, thereby facilitating rapid cleaning of such areas.
  • [0014]
    The treatment chamber can be a process chamber in which a fabrication process is conducted. Furthermore, the electron-beam irradiator can be the same as used to perform the fabrication process in the process chamber. For example, the electron-beam irradiator can be an illumination-optical system of an electron-beam microlithography apparatus. Alternatively, the electron-beam irradiator can be separate from an electron-optical system used to perform the fabrication process.
  • [0015]
    According to another aspect of the invention, electron-beam microlithography apparatus are provided that include a process chamber and an electron-optical system situated in the process chamber and configured to irradiate a surface of a substrate in a selective manner with an electron beam from a source. An embodiment of such an apparatus includes a treatment-gas source connected to and configured to introduce a treatment gas into the process chamber. Also inside the process chamber is a separate electron-beam irradiation device that is separate from the electron-optical system. The electron-beam irradiation device is configured to produce a respective electron beam that impinges on the treatment gas in the process chamber so as to ionize molecules of the treatment gas. The ionized molecules are available to react with and volatilize a contaminant deposit in the process chamber. By including a separate electron-beam irradiation device used for contaminant removal, this embodiment effectively removes contaminants from regions inside the process chamber not ordinarily irradiated by the electron beam from the electron-optical system.
  • [0016]
    According to another aspect of the invention, methods are provided for removing a deposit of a contaminant in a process chamber. In an embodiment of such a method, a treatment gas is provided that comprises molecules that become ionized when irradiated by electrons. The molecules of the treatment gas are introduced into the process chamber. When the process chamber contains molecules of the treatment gas, the molecules of the treatment gas are irradiated with the electron beam to ionize the molecules of the treatment gas. The ionized molecules of the treatment gas are allowed to react with and volatilize the deposit. Finally, the volatilized deposit is removed from the process chamber, such as by evacuating the process chamber.
  • [0017]
    In another embodiment of the method, a treatment gas is provided as summarized above. Molecules of the treatment gas are introduced into the process chamber. In the process chamber, an electron-beam irradiation device is provided that is configured to produce an electron beam. An electron-scattering body is placed in the process chamber such that the electron beam can impinge on the electron-scattering body to produce scattered electrons. When the process chamber contains molecules of the treatment gas, the electron-scattering body is irradiated with the electron beam to produce scattered electrons that ionize the molecules of the treatment gas. The ionized molecules are allowed to react with and volatilize the deposit. An advantage of this method is that the scattered electrons can propagate to regions inside the process chamber that otherwise are difficult to reach using a directly impinging electron beam. In any event, using such a method, there is no need to remove contaminated objects from the process chamber or to disassemble the apparatus associated with the process chamber. Consequently, throughput is not adversely affected to a significant degree.
  • [0018]
    Another method embodiment is directed to methods for cleaning a reticle in a process chamber of an electron-beam microlithography apparatus. According to the method, the reticle is placed in an interior space defined by the process chamber. A subatmospheric pressure (“vacuum”) is applied to the interior space. An electron beam is directed to impinge on the reticle in the process chamber as electrons of the beam passing through the reticle are deflected away from a resist-coated surface of a lithography substrate so as not to expose the resist.
  • [0019]
    The electron beam impinging on the reticle for reticle cleaning desirably has an energy sufficient to volatilize a deposit of a contaminant on the reticle as the reticle is being irradiated with the electron beam. This cleaning energy desirably is greater than the energy of the beam used to expose the resist-coated surface of the substrate with the reticle pattern.
  • [0020]
    The cleaning energy can be sufficient to confer a negative charge to the contaminant deposit and to cause the deposit to detach from the surface of the reticle. In this instance, it is desirable to provide a “dust collector” inside the process chamber. The dust collector is provided with a positive charge sufficient to attract the detached deposit, and thus used to collect the detached deposit.
  • [0021]
    According to another embodiment of a method, according to the invention, for performing microlithography, the reticle and substrate are placed in the process chamber. The reticle is situated so as to be irradiated with an upstream electron beam and to produce a downstream electron beam carrying an image of the irradiated region of the reticle. The substrate is situated such that its resist-coated surface can be exposed with the image carried by the downstream electron beam. The process chamber is evacuated to produce a subatmospheric pressure in the process chamber. In a reticle-cleaning mode of operation, the upstream electron beam is directed to impinge on the reticle while the downstream electron beam is directed away from the resist-coated surface so as to avoid exposing the resist. In a substrate-exposure mode of operation, the upstream electron beam is directed to irradiate a region on the reticle while the downstream electron beam is directed to a corresponding location on the resist-coated surface of the substrate so as to transfer the pattern from the reticle to the substrate. In the reticle-cleaning mode, the electron beam desirably has a first energy sufficient to volatilize a contaminant deposit on the reticle. In the substrate-exposure mode, the electron beam desirably has a second energy sufficient to expose the resist. The first energy desirably is greater than the second energy.
  • [0022]
    Because the reticle is cleaned in situ inside the evacuated process chamber of the microlithography apparatus, there is no need to break the vacuum of the process chamber to remove the reticle for remote cleaning. Hence, the reticle can be cleaned readily without a significant decrease in throughput. For example, the reticle can be cleaned before each use.
  • [0023]
    In the foregoing method, the process chamber can be provided with a dust collector that is provided with a positive charge during the reticle-cleaning mode. Hence, during the reticle-cleaning mode, the electron beam impinging on the reticle has an energy sufficient to confer a negative charge to a contaminant deposit on the reticle and to detach the deposit from the reticle. The detached deposit thus is attracted to and collected by the dust collector.
  • [0024]
    The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0025]
    [0025]FIG. 1 is a schematic elevational depiction (with partial sections) of a contamination-removal device according to a first representative embodiment of the invention.
  • [0026]
    [0026]FIG. 2 is a schematic elevational depiction (with partial sections) of an electron-optical lens column according to the second representative embodiment.
  • [0027]
    [0027]FIG. 3 is a schematic elevational diagram (with control aspects shown in block-diagram form) of an electron-optical lens column according to the second representative embodiment.
  • [0028]
    [0028]FIG. 4 is a schematic elevational depiction (with partial sections) of certain aspects of an electron-beam microlithography apparatus according to the third representative embodiment.
  • [0029]
    [0029]FIG. 5 is a schematic elevational depiction (with partial sections) of certain aspects of an electron-beam microlithography apparatus according to the fourth representative embodiment, including deflection of the beam in a reticle-cleaning mode of operation.
  • [0030]
    [0030]FIG. 6 is a schematic elevational depiction (with partial sections) of certain aspects of the electron-beam microlithography apparatus according to the fourth representative embodiment, in a wafer-exposure mode of operation.
  • [0031]
    [0031]FIG. 7 is a schematic elevational section of a portion of a scattering-stencil type reticle used in the fourth representative embodiment, including carbon particles situated on the upstream-facing surface of the reticle.
  • [0032]
    [0032]FIG. 8 is a block diagram of certain control relationships in the fourth representative embodiment.
  • [0033]
    [0033]FIG. 9 is an elevational schematic diagram of an electron-beam microlithography apparatus, as described in the fifth representative embodiment.
  • [0034]
    [0034]FIG. 10 is an elevational schematic diagram of an electron-beam microlithography apparatus, as described in the sixth representative embodiment.
  • [0035]
    [0035]FIG. 11 is an elevational schematic diagram of an electron-beam microlithography apparatus, as described in the seventh representative embodiment.
  • DETAILED DESCRIPTION
  • [0036]
    The invention is described below in the context of representative embodiments and examples that are not intended to be limiting in any way.
  • [0037]
    First Representative Embodiment
  • [0038]
    This embodiment is depicted in FIG. 1, and is directed to a contamination-removal device 1 according to the invention. The device 1 of FIG. 1 comprises a process chamber 3 in which the object 2 to be cleaned is situated, a vacuum pump 5 used to evacuate the interior of the process chamber 3, and a gas inlet 7 extending through a wall of the process chamber 3. The gas inlet 7 is used for introducing a treatment gas into the interior of the process chamber 3. During cleaning, the object 2 is mounted or otherwise placed on a stage 11 situated inside the process chamber 3. The process chamber 3 can be the same chamber in which an actual fabrication process (e.g., microlithography) is conducted on the object 2, or can be a separate chamber dedicated to use for cleaning the object 2. In the latter case, the process chamber 3 can be termed a “treatment chamber.”
  • [0039]
    The device 1 also includes an electron-beam-irradiation device 9 situated and configured to irradiate the object 2 with an electron beam. The electron-beam-irradiation device 9 includes an electron gun 13 and an electron-optical system 15 that are situated upstream of the stage 11. The electron gun 13 emits an electron beam 23 in the downstream direction. The electron-optical system 15 includes multiple electron-lenses and deflectors, and an aperture, that irradiate the object 2 on the stage 11 with the electron beam emitted from the electron gun 13.
  • [0040]
    An evacuation outlet 17 extends from the process chamber 3 and is connected to the vacuum pump 5 for evacuating the atmosphere inside the process chamber 3. The gas inlet 7 is connected to a gas cylinder 21 via valves 19. The gas cylinder 21 provides a supply of a gas such as water vapor, oxygen, ozone, or oxygen radicals, or a mixture of such gases.
  • [0041]
    For cleaning, the object 2 is placed on the stage 11 inside the process chamber 3. The vacuum pump 5 is turned on to evacuate the interior of the process chamber 3. After reaching a desired vacuum, the vacuum pump is turned off and the valves 19 are opened to allow flow of the gas from the gas cylinder 21 through the gas inlet 7 into the process chamber 3. When the interior of the process chamber 3 is sufficiently filled with the gas, the electron beam 23 is directed in a downstream direction from the electron-beam-irradiation device 9. The electron beam 23 ionizes the gas molecules inside the process chamber 3. The ionized gas molecules oxidize molecules of the contaminants adhering to the object 2. As a result, the contaminants are broken down and volatilized.
  • [0042]
    After irradiating the object 2 with the electron beam for a specified period of time, the vacuum pump 5 is turned on again to evacuate the process chamber 3. This evacuation draws volatilized contaminants from the process chamber 3.
  • [0043]
    If the area of the object 2 is large, then electron beam 23 can be deflected as required by a deflector or the like of the electron-optical system 15 to direct the beam 23 to various regions on the surface of the object 2. This deflection can be in a scanning manner, or the stage 11 can be moved in a scanning manner in the horizontal direction (in the figure), to allow the entire surface of the object 2 to be irradiated with the electron beam 23.
  • [0044]
    Second Representative Embodiment
  • [0045]
    This embodiment is shown in FIGS. 2 and 3. Turning first to FIG. 3, an electron-optical lens column 31 is situated in an upper portion (in the figure) of an electron-beam microlithography apparatus 30. The lens column 31 is a chamber that can be evacuated. To such end, a vacuum pump 32 is connected to the lens column 31. At the upper end (in the figure) of the lens column 31 is an electron gun 33 that emits an electron beam in a downstream direction. From the electron gun 33, the beam passes through a condenser lens 34, passes a deflector 35, and impinges on a reticle M, in that order. The condenser lens 34 converges the electron beam emitted from the electron gun 33. The electron beam is scanned in the lateral direction (in the figure) by the deflector 35 to illuminate every region on the reticle M within the optical field of the electron-optical system.
  • [0046]
    The reticle M is fastened by electrostatic adhesion or the like to a reticle chuck 40 installed on an upstream-facing surface of a reticle stage 41. The reticle stage 41 is mounted to and supported by a base plate 46 or analogous support. The reticle stage 41 is driven by an actuator 42 connected to the reticle stage 41. The actuator 42 is connected to a controller 45 via a stage driver 44. A laser interferometer 43 is situated on one side (right side in the figure) of the reticle stage 41. The laser interferometer 43 is connected to the controller 45. The laser interferometer 43 produces data, concerning the position of the reticle stage 41, that is input to the controller 45. Based on the data, the controller 45 routes commands to the stage driver 44 to operate the actuator 42 to drive the reticle stage 41 to a desired target position.
  • [0047]
    A “wafer chamber” 51 (another vacuum chamber, and representative of a process chamber) is situated downstream of the base plate 46. A vacuum pump 52 is connected to the wafer chamber 51 (on the right side in the figure) to allow evacuation of the interior of the wafer chamber 51. Inside the wafer chamber 51 are a projection lens 54, a deflector 55, and a substrate (“wafer”), in that order. The electron beam passing through the reticle M is converged by the projection lens 54 and deflected by the deflector 55 as required to form an image of the illuminated region of the reticle M in a specified position on the wafer W.
  • [0048]
    The wafer W is fastened by electrostatic adhesion or the like to a wafer chuck 60 situated on the upstream-facing surface of a wafer stage 61. The wafer stage 61 is mounted on a base plate 66 or analogous support. The wafer stage 61 is movable as required by an actuator 62 connected to the wafer stage 61. The actuator 62 is connected to the controller 45 via a stage driver 64. A laser interferometer 63 is situated to the side of the wafer stage 61 (i.e., on the right side in the figure). The laser interferometer 63 is connected to the controller 45. The laser interferometer 63 produces data concerning the position of the wafer stage 61. This data is routed to and input to the controller 45. The controller 45 routes commands to the driver 64 to cause the actuator 62 to move the wafer stage 61 to a desired target position.
  • [0049]
    Turning now to FIG. 2, the electron-optical system and reticle of the apparatus of FIG. 3 are shown in simplified form. As noted above, the vacuum pumps 32, 52 are connected to the lens column 31 and wafer chamber 51, respectively, of the apparatus 30. A gas inlet 71 opens into the lens column 31 or the wafer chamber 51 (or both). The gas inlet 71 is connected to a gas cylinder 75 via valves 73. The gas cylinder 75 supplies a gas such as water vapor, oxygen, ozone, or oxygen radicals, or a mixture of such gases.
  • [0050]
    To remove contamination from the interior of the apparatus 30, a scattering body 77 can be placed on (for example) the reticle stage 41 or the wafer stage 61. The scattering body 77 desirably has a plate configuration and desirably is made of or plated with a “heavy” metal such as tungsten, tantalum, gold, or platinum. Even more desirably, the upstream-facing surface of the scattering body 77 defines multiple fine recesses and projections. The valves 73 are opened to introduce the gas from the gas cylinder 75 via the gas inlet 71 into the lens column 31 and vacuum chamber 51. After sufficiently filling the respective interiors of the lens column 31 and vacuum chamber 51 with the gas, the upstream-facing surface of the scattering body 77 is irradiated with an electron beam 81. Such irradiation generates backscattered electrons 79. The upstream-facing surface of the scattering body desirably includes fine recesses and projections to facilitate scattering of electrons in all directions from the scattering body 77.
  • [0051]
    The backscattered electrons 79 ionize molecules of the gas in the lens column 31 and wafer chamber 51. The ionized gas molecules react with deposits of contaminants inside the chambers 31, 51, causing breakdown and volatilization of the deposits. Since the backscattered electrons 79 propagate in all directions inside the lens column 31 and vacuum chamber 51, regions that ordinarily are difficult to irradiate (e.g., lenses, deflectors, and the downstream-facing surfaces of apertures) are irradiated by the backscattered electrons. Thus, contaminant deposits on all surfaces inside the chambers 31, 51 are broken down and volatilized. After irradiating in this manner for a specified period of time, the vacuum pumps 32, 52 are turned on to evacuate the lens column 31 and wafer chamber 51 and remove the volatilized contaminants.
  • [0052]
    Third Representative Embodiment
  • [0053]
    This embodiment, directed to an electron-beam microlithography apparatus 30, is depicted schematically in FIG. 4. This embodiment includes an electron-beam (e-beam) irradiation device 83 used for removal of contaminants. The e-beam irradiation device 83 is situated inside the lens column 31 or wafer chamber 51 (or both). The e-beam irradiation device 83 is separate from the electron gun 33 used for lithographic exposure. The e-beam irradiation device 83 includes an electron gun 85 and an electron-optical system 87. The electron-optical system 87 typically includes multiple lenses, deflectors, and an aperture (not shown). Vacuum pumps 32, 52 are connected to the lens column 31 and wafer chamber 51, respectively. A gas inlet 71 extends into the lens column 31 or wafer chamber 51, or both. The gas inlet 71 is connected to a gas cylinder 75 via valves 73. The gas cylinder 75 is filled with a gas such as water vapor, oxygen, ozone, or oxygen radicals, or mixture thereof.
  • [0054]
    To remove contamination from the interior of the apparatus 30, the interiors of the lens column 31 and wafer chamber 51 are filled with the gas from the gas cylinder 75. The electron beam 81 from the electron gun 33 used for lithographic exposure is deflected and scanned in the interior of the apparatus 30. Also, an electron beam 89 is emitted from the e-beam irradiation device 83. Desirably, the e-beam irradiation device 83 is situated such that the electron beam 89 emitted therefrom is directed to locations that are beyond the irradiation range of the exposure electron beam 81, and that are most susceptible to contamination inside the lens column 31 and wafer chamber 51.
  • [0055]
    Gas molecules ionized by the electron beams 81, 89 react with deposits of contaminants adhering to the interior surfaces of the chambers 31, 51. Thus, the contaminants are oxidized, broken down, and volatilized. Electron-beam irradiation is continued for a specified period of time, after which the vacuum pumps 32, 52 are turned on to evacuate the lens column 31 and wafer chamber 51. Thus, the volatilized molecules of the contaminants are removed from the chambers.
  • [0056]
    Any of the various embodiments described above achieve removal of contaminants from the interior of a chamber of, e.g., a microlithographic exposure apparatus without reducing throughput or having to disassemble or remove components from the apparatus.
  • EXAMPLE 1
  • [0057]
    The test object for cleaning was a silicon stencil reticle with adhering deposits of hydrocarbon contaminants that accumulated during electron-beam irradiation of the reticle. The test object was placed in the sample chamber of a scanning electron microscope, and water vapor was introduced into the sample chamber. The contaminated test object was scanned and irradiated with an electron beam, accelerated across a voltage of 20 kV, in a 600-Pa atmosphere in the sample chamber. Under such conditions, the contaminants adhering to the silicon stencil reticle were removed successfully.
  • EXAMPLE 2
  • [0058]
    The test object for cleaning was a silicon stencil reticle with adhering deposits of hydrocarbon contaminants that accumulated during electron-beam irradiation of the reticle. The test object was placed in the sample chamber of a scanning electron microscope, and oxygen gas was introduced into the sample chamber. The contaminated test object was scanned and irradiated with an electron beam, accelerated across a voltage of 20 kV, in a 600-Pa atmosphere in the sample chamber. Under such conditions, the contaminants adhering to the silicon stencil reticle were removed successfully.
  • EXAMPLE 3
  • [0059]
    The test object for cleaning was a silicon stencil reticle with adhering deposits of hydrocarbon contaminants that accumulated during electron-beam irradiation of the reticle. The test object was placed in the sample chamber of a scanning electron microscope, and ozone gas was introduced into the sample chamber. The ozone gas was generated using an ozonizer that converts oxygen into ozone. The contaminated test object was scanned and irradiated with an electron beam, accelerated across a voltage of 30 kV, in a 400-Pa atmosphere in the sample chamber. Under such conditions, the contaminants adhering to the silicon stencil reticle were removed successfully.
  • EXAMPLE 4
  • [0060]
    The test object for cleaning was a metal aperture, made of molybdenum, as used in an electron-optical system. The test object had adhering deposits of hydrocarbon contaminants. The test object was placed in the sample chamber of a scanning electron microscope, and a mixture of water vapor and oxygen gas was introduced into the sample chamber. The contaminated test object was scanned and irradiated with an electron beam, accelerated across a voltage of 30 kV, in a 600-Pa atmosphere in the sample chamber. Under such conditions, the contaminants adhering to the metal aperture were removed successfully.
  • EXAMPLE 5
  • [0061]
    A scattering body was configured as a tungsten plate. The scattering body was placed on the wafer stage of an electron-beam microlithography apparatus inside a wafer chamber. Oxygen gas was introduced into the wafer chamber. The scattering body was irradiated with an electron beam, accelerated across a voltage of 100 kV, in a 1000-Pa atmosphere in the wafer chamber. Afterward, the interior of the wafer chamber was evacuated. Under such conditions, the contaminants adhering to various locations inside wafer chamber and lens column of the electron-beam microlithography apparatus were removed.
  • [0062]
    Fourth Representative Embodiment
  • [0063]
    This embodiment is directed to cleaning of the reticle as used in a CPB microlithography apparatus. The reticle is cleaned in situ by the CPB microlithography apparatus operated in a “reticle-cleaning” mode. Reticle cleaning can be performed prior to operating the apparatus in a “wafer-exposure” mode, so as to prepare the reticle for use in exposure. During reticle cleaning, contaminants are removed by irradiating the reticle with a charged particle beam (e.g., an electron beam).
  • [0064]
    An electron-beam microlithography apparatus according to this embodiment is shown in FIG. 5. The components used for exposure and for reticle cleaning are contained in a vacuum chamber 120. For exposure and reticle cleaning, the interior of the vacuum chamber 120 is maintained at a desired level of “vacuum” (subatmospheric pressure) by means of a vacuum pump 121. Under such conditions, it is possible to select either the wafer-exposure mode or the reticle-cleaning mode without having to change the vacuum.
  • [0065]
    An electron gun 101 emits an electron beam 103 in a downstream trajectory at an acceleration voltage of, e.g., 100 kV. A reticle 104 is placed on a reticle stage 105 situated downstream of the electron gun 101. The electron beam 103 emitted from the electron gun 101 is collimated by an illumination lens 102 for irradiation of the reticle 104. At any given instant, the irradiation field on the reticle 104 is, e.g., 1-mm square.
  • [0066]
    The reticle 104 can be a scattering-stencil reticle comprising a reticle membrane made of a material that scatters incident electrons of the beam and that defines through-holes that are transmissive to the incident beam. The pattern of through-holes in the membrane defines the elements of the pattern to be transferred to a substrate (wafer) 109. Alternatively, the reticle can be a scattering-membrane reticle comprising regions of an electron-scattering material formed on the surface of a thin base membrane that is relatively transmissive to the incident beam. In either case, the electron-scattering portions of the reticle are sufficiently thin to prevent significant absorption of incident electrons, thereby preventing excessive heating of the reticle that otherwise would occur by absorption of incident electrons. By way of example, in a scattering-stencil reticle configuration, the reticle membrane is made of silicon with a thickness of 2 μm.
  • [0067]
    The apparatus of FIG. 5 also includes a first lens 106 and a second lens 108 of a projection-lens system. The lenses 106, 108 are situated along an optical axis A at a spacing of 50 mm beneath the reticle 104. A “contrast diaphragm” 107 is situated between the lenses 106, 108. The contrast diaphragm 107 is made of a tantalum or other heavy metal plate having a thickness of, e.g., 1 mm and defining an axial aperture having a diameter of, e.g., 150 μm. The contrast diaphragm is situated in the vicinity of the Fourier plane of the reticle 104. The contrast diaphragm 107 blocks downstream propagation of scattered electrons so that only the electrons passing through the aperture propagate downstream of the contrast diaphragm. I.e., electrons scattered while passing through the reticle 104 are blocked by the contrast diaphragm 107.
  • [0068]
    A movable wafer stage 110 is situated in the lower part (in the figure) of the depicted apparatus. A substrate (wafer) 109 is mounted on the wafer stage 110 for exposure. So as to be imprinted with an image of the pattern on the reticle 104, the surface of the wafer 109 is coated with a resist, either directly or with an interposed insulating film or conductive film.
  • [0069]
    At least one deflector 112 is used to deflect the electron beam 111 as required. During operation of the apparatus in the reticle-cleaning mode, the reticle 104 is irradiated by the electron beam 111. Electrons of the beam passing through the reticle 104 are deflected laterally by the deflector 112 in a manner causing the electron beam 111 to enter a Faraday cup 123 situated on the wafer stage 110. Thus, during such deflection, the electron beam 111 does not irradiate the resist on the wafer 109. The Faraday cup 123 can be movable so as to be situated on the wafer stage 110 only in the reticle-cleaning mode. Alternatively, it is possible to actuate the wafer stage 110 to move the Faraday cup 123 thereon into a position at which the Faraday cup 123 can capture the electron beam 111 more easily.
  • [0070]
    In the reticle-cleaning mode, the electron beam 103 irradiates the reticle 104 in the same sequence as in the wafer-exposure mode. Either of the following two methods may be used to remove contaminants adhering to the reticle 104. In the first method the contaminants are heated to a high temperature and volatilized. To such end, the beam intensity (current) of the electron beam 103 desirably is increased above the beam intensity used in the wafer-exposure mode, so as to heat the contaminants to a high temperature as quickly as possible. For example, the beam intensity can be 50 μA in the wafer-exposure mode and 100 μA in the reticle-cleaning mode. The electron-beam irradiation time is described in detail later below. In the second method cleaning is accomplished by charging the contaminants adhering to the reticle 104 with a negative charge (by electron-beam irradiation). The contaminants are collected using a dust collector 122 flanking the reticle 104 and energized with a positive potential. In either method, the microlithography apparatus shifts to the wafer-exposure mode after the completing the reticle-cleaning mode.
  • [0071]
    [0071]FIG. 6 depicts the electron-beam microlithography apparatus configured for operation in the wafer-exposure mode. In this mode, the electron gun 101 emits the electron beam 103 in a downward direction (in the figure), accelerated under a voltage of, e.g., 100 kV. The electron beam 103 emitted from the electron gun 101 is collimated by the illumination lens 102 for illumination of the reticle 104. Also shown are the first and second projection lenses 106, 108, respectively, and the deflector 112. During wafer exposure, defined regions (“subfields”) of the reticle 104 are irradiated sequentially. Meanwhile, respective images of the irradiated subfields are formed at predetermined regions on the wafer 109. These exposure regions on the wafer 109 are determined by the deflector 112 such that, upon completing exposure of the reticle pattern onto the wafer 109, the individual subfield images are “stitched” together properly. As each subfield images is projected onto the wafer, the resist in the exposure location is imprinted with the portion of the overall pattern defined by the irradiated subfield. Usually, the size of the image as formed on the wafer 109 is “reduced” (demagnified) relative to the size of the corresponding pattern on the wafer. For example, the reduction can be .
  • [0072]
    During wafer exposure, exposure time is a function of exposure parameters such as the resist sensitivity, beam current, stage velocity, and other variables. For example, the resist can have a sensitivity of 5 μC/cm2, and the exposure time for one subfield can be 62.5 μsec at a beam current (on the reticle) of 50 μA.
  • [0073]
    Beam intensity and irradiation time during the reticle-cleaning mode (in which contaminants are removed by heating using the electron beam) are discussed with reference to FIG. 7. In the figure, a scattering-stencil reticle 104 is shown having membrane regions 114 and through-holes 115. As representative particulate contaminants, carbon particles 117 are situated on the upstream-facing surface of the reticle 104. The particles 117 have a diameter of 0.4 μm. The electron beam 103 directed onto the reticle 104 is scattered by the membrane regions 114 and transmitted by the through-holes 115.
  • [0074]
    In the following calculations, the carbon particles 117 are approximated by cubes measuring 0.4 μm on each side. Assuming that the carbon particles 117 have the approximate density of graphite, the density of the particles is 2.27106 g/m3, and the specific heat of the particles is 0.669 J/gK.
  • [0075]
    The absorption by the particles 117 of electron-beam energy can be expressed using the Bethe equation:
  • dE/dx=1.268109 eV/m
  • [0076]
    Accordingly, the amount of electron-beam energy absorbed by a carbon particle (having a thickness of 0.4 μm) is:
  • dE=(1.268109 eV/m)(0.410−6 m)=5.07102 eV
  • [0077]
    Assuming that the electron beam is accelerated under a voltage of 100 kV, the ratio of the amount of energy absorbed by the particle to the acceleration energy is:
  • (5.07102 eV)/(105 eV)≈0.5%
  • [0078]
    Assuming a beam intensity of 100 μA, the total beam energy applied in one second to an irradiation area of 1 mm2 is:
  • (100 kV)(100 μA)(1 sec)=(1105 J/As)(110−4 A)(s)=10 J
  • [0079]
    Accordingly, the beam energy irradiated on a carbon particle measuring 0.4 μm on a side is:
  • (10 J)[(0.4106 m)/(110−3 m)]2=1.610−6 J
  • [0080]
    Since the energy absorbed by the carbon particles is 0.5% of the incident beam energy, the absorbed energy is 810−9 J.
  • [0081]
    The mass of each carbon particle is determined from the density and volume of the particle:
  • (2.27106 g/m3)(0.410−6 m)3=1.4510−13 g
  • [0082]
    Since the carbon particles merely are resting on the surface of the reticle with minimal thermal contact with the reticle, it is assumed that no heat is conducted from the carbon particles to the reticle. In such a case, the temperature rise ΔT of the carbon particles is determined as follows:
  • ΔT=(810−9 J)/[(0.669 J/gK)(1.4510−13 g)]=8.2104 K
  • [0083]
    In other words, if electron-beam irradiation of the reticle were performed for 1 second under the conditions described above, the temperature of each carbon particle would be increased by approximately 82,000 K. Since the vaporization temperature of carbon is approximately 4900 C., irradiation with the electron beam for approximately 60 msec causes the temperature of the carbon particles to rise approximately 5500 degrees, which causes the carbon particles to evaporate. Thus, as described above, reticle cleaning can be accomplished in a short time by irradiating the reticle with the electron beam having a higher intensity than used for wafer exposure.
  • [0084]
    The reticle 104 shown in FIG. 7 is a scattering-stencil reticle in which only a small percent of incident beam energy is absorbed. The heat generated by this absorbed energy is conducted to the reticle stage. During reticle cleaning as described above, the temperature rise of the reticle is actually about the same as encountered by the reticle during the wafer-exposure mode. Consequently, the reticle temperature does not increase to a level at which the reticle could be damaged. Also, since the surfaces of particles of carbon and other contaminants normally are oxidized, conditions for poor heat conduction between the reticle and the particles are fairly well satisfied if the thermal-contact resistance between the reticle and the particles is taken into account. Furthermore, the electron-beam irradiation conditions are not limited to the specific conditions described above; actual conditions should be determined based on the materials and dimensions of the reticle and the contaminants.
  • [0085]
    The example described above was in the context of carbon particles that exhibit low absorption of the incident electrons of the beam. Metal particles, on the other hand, exhibit relatively high absorption of incident electrons. Consequently, metal particles would be volatilized in a shorter time than carbon particles.
  • [0086]
    In addition, the reticle-cleaning mode can be effective in removing contaminants (e.g., burned-on carbon-type contaminants) that cause local accumulations of charge that can affect the beam trajectory adversely. Whenever charge-accumulation occurs, the electrical conductivity of the reticle tends to drop, which results in poorer thermal conductivity between the particulate contaminants and the reticle. Under such conditions, the contaminants can be volatilized readily in the same manner as described above.
  • [0087]
    A block diagram showing control relationships of this embodiment is shown in FIG. 8. The intensity of the electron beam emitted from the electron gun 101 is controlled by an electron-gun controller 134 connected to a main controller 131. The operational parameters of the respective lenses 102, 106, 108 are controlled by a lens-coil power supply 140 also connected to the main controller 131. Similarly, the operational parameters of the deflector 112 are controlled by a deflector-coil power supply 141 also connected to the main controller 131.
  • [0088]
    The reticle 104 is mounted to the upstream-facing surface of the reticle stage 105. A reticle-stage controller 133, also connected to the main controller 131, controls the position of the reticle stage 105. Respective position detectors 135 (e.g., laser interferometers) detect the position of the reticle stage 105. Data produced by the position detectors 135 are routed to the main controller 131 via respective data interfaces 136. Stage-control data from the reticle-stage controller 133 are input into a statistical calculator 132. The statistical calculator 132 is configured to optimize, from the results of statistical calculations performed by the statistical calculator, the relative positions of the reticle and wafer.
  • [0089]
    Similarly, a wafer-stage controller 137, also connected to the main controller 131, controls the position of the wafer stage 110. Respective position detectors 138 (e.g., laser interferometers) detect the position of the wafer stage 10. Data produced by the position detectors 138 are routed to the main controller 131 via respective data interfaces 139. Stage-position data from the position detector 138 and data from the wafer-stage controller 137 are input into the statistical calculator 132.
  • [0090]
    In the reticle-cleaning mode, the main controller 131 controls the electron-gun controller 134 to cause the electron gun 101 to direct an electron beam toward the reticle 104. The main controller 131 also controls the deflector-coil power supply 141 so as to cause the deflector 112 to deflect the electron beam (passing through the reticle 104) sufficiently to cause the electron beam to intersect the wafer plane outside an area coated with resist. The main controller 131 also causes a positive potential to be applied to the Faraday cup 123 so as to cause the electron beam to be conducted to the Faraday cup 123.
  • [0091]
    In the alternative method in which cleaning is performed by collecting particulate contaminants, released from the reticle, using a dust collector 122, the main controller 131 controllably operates the dust collector 122 in the reticle-cleaning mode. Specifically, at the time the electron beam is directed toward the reticle 104, or immediately after such irradiation of the reticle, a positive potential is applied to the dust collector 122 so that negatively charged contaminants released from the reticle are attracted to and collected in the dust collector 122. In cases in which dust collection is performed simultaneously with electron-beam irradiation of the reticle, the dust collector desirably is situated at a position that does not affect the trajectory of the beam.
  • [0092]
    In the wafer-exposure mode, the main controller 131 controllably operates the electron-gun controller 134 to cause the electron gun 101 to direct the electron beam toward the reticle 104. The main controller 131 also controllably operates the deflector-coil power supply 141 to cause the deflector 112 to scan the electron beam over the resist on the wafer so as to imprint the resist with the reticle pattern as projected onto the wafer surface.
  • [0093]
    Fifth Representative Embodiment
  • [0094]
    [0094]FIG. 9 shows certain imaging and control relationships of an electron-beam microlithography apparatus according to a representative embodiment. Although this embodiment employs an electron beam as a lithographic energy beam, it will be understood that the principles of this embodiment can be applied with equal facility to use of an alternative charged particle beam, such as an ion beam.
  • [0095]
    The apparatus of FIG. 9 comprises an illumination-optical system IOS and a projection-optical system POS arranged along an optical axis AX. The illumination-optical system IOS comprises optical components situated between an electron gun 201 and a reticle 210, and the projection-optical system POS comprises optical components situated between the reticle 210 and a substrate 223. So as to be imprinted with the pattern as projected from the reticle by the projection-optical system POS, the upstream-facing surface of the substrate 223 is coated with a suitable “resist,” thereby rendering the substrate “sensitive” to exposure by the electron beam. The substrate 223 can be any suitable material and configuration, such as a silicon wafer.
  • [0096]
    At the extreme upstream end of the apparatus, the electron gun 201 emits an electron beam (“illumination beam”) in a downstream direction through the illumination-optical system IOS. The illumination-optical system comprises first and second condenser lenses 202, 203, respectively, a beam-shaping aperture 204, a blanking aperture 207, an illumination-beam deflector 208, and an illumination lens 209. The illumination beam from the electron gun 201 passes through the condenser lenses 202, 203, which converge the beam at a crossover C.O. situated at the blanking aperture 207.
  • [0097]
    The beam-shaping aperture 204 is situated downstream of the second condenser lens 203. The beam-shaping aperture has a profile (e.g., rectangular) that peripherally trims the illumination beam as the beam passes through the beam-shaping aperture. Thus, the illumination beam is trimmed to have a transverse profile that is shaped and dimensioned to illuminate a single exposure unit (e.g., a single subfield) on the reticle 210. For example, the beam-shaping aperture 204 trims the illumination beam to have a square transverse profile with side dimensions of slightly greater than 1 mm as incident on the reticle 210. A focused image of the beam-shaping aperture 204 is formed on the reticle 210 by the illumination lens 209.
  • [0098]
    As noted above, the blanking aperture 207 is situated, downstream of the beam-shaping aperture 204, at the crossover C.O. The blanking aperture includes an aperture plate 207 p that defines an axial through-aperture 207 a. During times when the illumination beam is “blanked” (prevented from propagating to the reticle 210), the blanking deflector 205 deflects the illumination beam off-axis as required to cause the beam to be incident on the aperture plate 207 p rather than on the through-aperture 207 a. Incidence of the illumination beam on the aperture plate 207 p blocks the beam from propagating to the reticle 210.
  • [0099]
    The illumination-beam deflector 208 is situated downstream of the blanking aperture 207, and is configured mainly for scanning the illumination beam in the X-direction in FIG. 9 to as to illuminate successive subfields on the reticle 210 in a sequential manner. The respective subfields that are illuminated per scan (“sweep”) of the beam are in a respective row on the reticle located within the optical field of the illumination-optical system IOS. The illumination lens 209 is situated downstream of the illumination-beam deflector 208. The illumination lens 209 is a condenser lens that collimates the illumination beam for impingement on the reticle 210. Also, as noted above, the illumination lens 209 forms a focused image of the beam-shaping aperture 204 on the upstream-facing surface of the reticle 210.
  • [0100]
    In FIG. 9 only one subfield of the reticle 210 is shown, situated on the optical axis AX. In actuality, the reticle 210 comprises a large number of subfields, arrayed in the reticle plane extending in the X- and Y-directions (i.e., the X-Y plane). Typically, the reticle 210 defines the pattern for a layer of a microelectronic device, for example an integrated circuit. (The pattern for one layer need not be defined by only one reticle.) The pattern normally extends sufficiently to occupy a “die” on the substrate 223. To ensure that the illumination beam illuminates a particular subfield on the reticle 210, the illumination-beam deflector 208 is energized appropriately.
  • [0101]
    The reticle 210 is mounted on a reticle stage 211 that can be moved in the X- and Y-directions. Similarly, the substrate 223 is mounted on a substrate stage 224 that also is movable in the X- and Y-directions. During imaging of the pattern, the subfields residing in a particular row within the optical field of the illumination-optical and projection-optical systems are illuminated sequentially by scanning (“sweeping”) the illumination beam in the X-direction (synchronously with scanning of the “imaging beam,” propagating downstream of the reticle 210, in the X-direction). The respective width of each row in the X-direction on the reticle and substrate is essentially the width of the optical field of the illumination-optical system and projection-optical system, respectively. To progress from one row to the next (and hence expose subfields outside the optical field), the reticle stage 211 and substrate stage 224 undergo respective continuous scanning motions in the Y-direction. Both stages 211, 224 are provided with respective position-measurement systems 212, 225 (typically laser interferometers) that accurately measure the position of the respective stage in the X-Y plane in real time. These accurate positional measurements are critical for achieving proper alignment and “stitching” together of subfield images as projected onto the substrate 223.
  • [0102]
    The projection-optical system POS comprises first and second projection lenses 215, 219, respectively, and a deflector 216 all situated downstream of the reticle 210. As the illumination beam is irradiated on a selected subfield of the reticle 210, portions of the beam are transmitted through the reticle while becoming imaged with the respective portion of the reticle pattern defined by the particular subfield. Hence, the beam propagating downstream of the reticle 210 is termed the “imaging beam” or “patterned beam.” The patterned beam passes through the projection-optical system POS to the substrate 223. In this regard, as the patterned beam passes through the projection lenses 215, 219, the image carried by the patterned beam is “demagnified,” usually by an integer factor. Hence, the projection lenses 215, 219 collectively have a “demagnification ratio” such as or ⅕. The patterned beam is deflected by the deflector 216 and focused at a specified location on the substrate 223. Also, due to the optical behavior of the projection-optical system POS, the respective directions of sweeps of the illumination beam and patterned beam in the X-direction are mutually opposite, and the respective directions of motion of the stages in the Y-direction also are mutually opposite.
  • [0103]
    As noted above, the upstream-facing surface of the substrate 223 is coated with a suitable resist. Whenever a specified dose of the patterned beam impinges on the resist, the area of impingement is imprinted with the image carried by the patterned beam.
  • [0104]
    A crossover C.O. is situated on the axis AX at a point at which the axial distance between the reticle 210 and the substrate 223 is divided according to the demagnification ratio of the projection lenses 215, 219. A contrast aperture 218 is situated at the crossover. The contrast aperture 218 blocks portions of the patterned beam that experienced scattering upon passage through the reticle 210. Thus, the scattered electrons do not propagate to the substrate where they otherwise could degrade image contrast.
  • [0105]
    A backscattered-electron (BSE) detector 222 is situated directly upstream of the substrate 223. The BSE detector 222 is configured to detect and quantify electrons backscattered from certain marks on the substrate 223 and the substrate stage 224. For example, a mark on the substrate 223 is scanned by patterned beam produced by passage of the illumination beam through a corresponding mark pattern on the reticle 210. Detecting of backscattered electrons in this manner provides data from which the relative positional relationship of the reticle 210 and substrate 223 can be determined.
  • [0106]
    The substrate 223 is mounted on the substrate stage 224 via an electrostatic chuck (not shown but well understood in the art). By simultaneously moving the reticle stage 211 and substrate stage 224 in mutually opposite directions in respective continuous-scanning motions, it is possible to expose each portion of the pattern in a sequential manner. Meanwhile, the position detectors 212, 225 monitor the respective stage position in real time.
  • [0107]
    Each of the lenses 202, 203, 209, 215, 219 and each of the deflectors 205, 208, 216 is connected to a respective driver 202 a, 203 a, 209 a, 215 a, 219 a, and 205 a, 208 a, 216 a that supplies electrical power to the lens or deflector. Similarly, each of the stages 211, 224, is connected to a respective driver 211 a, 224 a that supplies electrical power to the respective stage 211, 224. Each of the drivers 202 a, 203 a, 205 a, 208 a, 209 a, 211 a, 215 a, 216 a, 219 a, 225 a is connected to a main controller 231 that generates and routes respective control signals for the drivers, thereby achieving controlled actuation of the lenses, deflectors, and stages. The main controller 231 also receives respective positional data from the respective position-measurement systems 212, 225, which are connected to the main controller 231 via respective data-interface units 212 a, 225 a. The data interfaces 212 a, 225 a include amplifiers, analog-to-digital (A/D) converters, and other processing circuitry necessary to interface the data from the position-measurement systems 212, 225 to the main controller 231. A similar data-interface 222 a connects the BSE detector 222 to the main controller 231.
  • [0108]
    The main controller 231 ascertains and quantifies control errors associated with stage positions, and actuates the deflector 216 as required to compensate for the control error. Thus, a reduced (demagnified) image of an irradiated reticle subfield is accurately transferred to a target position on the substrate 223. The subfield images are formed on the substrate 223 so as to “stitch” them together in a contiguous manner to form a complete die pattern.
  • [0109]
    Sixth Representative Embodiment
  • [0110]
    This embodiment addresses situations in which irradiation of the reticle in the manner described in the fourth representative embodiment could damage the reticle. In other words, heat generated by directly irradiating the reticle may have an undesired effect depending upon reticle size and thickness.
  • [0111]
    Particulate matter (e.g., particles generated from mechanical rubbing of machine parts such as stages) are removed by irradiating a focused ion beam (or electron beam) on the offending particle on the reticle in the presence of a corrosive gas. Bombardment of the ion beam on molecules of the gas in the vicinity of the offending particle ionizes the molecules near the particle. The ionized molecules are chemically reactive and essentially etch away the particle by volatilization. The volatilized molecules of the particle are evacuated using a vacuum pump or analogous appliance.
  • [0112]
    Reference is made to FIG. 10, depicting a process chamber 301 containing an electron-beam microlithography apparatus such as that shown in FIG. 9 and described in the fifth representative embodiment. The microlithography apparatus comprises an electron gun 201 (e.g., as shown in FIG. 9), an illumination-optical system 303, and a projection-optical system 304, all contained within the process chamber 301. For exposure and cleaning, a reticle 210 is situated on a reticle stage (not shown, but see the fifth representative embodiment) between the illumination-optical system 303 and the projection-optical system 304 as shown. The process chamber 301 is evacuated to a suitable vacuum level by a vacuum pump 302.
  • [0113]
    For inspection, the reticle 210 is moved, by appropriate lateral motion of the reticle stage, to the left in the figure to a detecting system 320. (The reticle in the inspection position is denoted 210′.) Thus, the reticle 210′ is situated so as to be illuminated by a “probe light” produced by the detecting system 320. Specifically, the detecting system 320 comprises a source 321 of probe light, a probe-light illumination system 322, and a detector 323, all situated within the process chamber 301. The detector 323 is connected to an image process 324, which is connected to a memory 325.
  • [0114]
    The probe light produced by the source 321 can be, for example, UV light, deep UV light, or an electron beam. The detector 323 can be a CCD, for example. The probe-light illumination system 322 is configured to direct a beam of the probe light selectively to any of various locations on the reticle, such as an upstream-facing surface or a side wall of an aperture in the reticle.
  • [0115]
    During inspection of the reticle 210′, the memory 325 preserves data concerning the respective locations of the contaminant deposit(s) on the reticle 310′. After inspection of the reticle 210′ is completed, the reticle stage returns the reticle 210 to its normal exposure position between the illumination-optical system 303 and the projection-optical system 304.
  • [0116]
    At the exposure position, the reticle 210 can be cleaned. The reticle stage positions the reticle 210 (according to data stored in the memory 325) to align the contaminant deposit with an electron beam or ion beam from the source 301 and passing through the illumination-optical system 303. Meanwhile, a reactive gas is introduced into the process chamber, in the vicinity of the reticle 210, by a gas supply 310.
  • [0117]
    The gas supply 310 includes a supply 311 of an inert gas, a supply 312 of a reactive gas, a flow controller 313 to which the supplies 311, 312 are connected, and a nozzle 314 extending into the process chamber 301 to discharge gas in the vicinity of the reticle 210. Exemplary reactive gases include any of various fluoride gases such as F2, CF4, CHF3, CH3F, SF6, XeF2, and WF6 for reaction with Ta or Si; any of various chloride gases such as Cl2, CCl4, CHCl3, CH2Cl2, CH3Cl, SiCl4, and Al2Cl6 for reaction with Al or Cr or Fe—Ni; or any of various bromide gases such as Br2 and CBr4 for reaction with Si.
  • [0118]
    The inert gas is used to facilitate, if required, generation of a plasma of the reactive gas to etch the contaminant deposit. The inert gas can be, for example, nitrogen or oxygen.
  • [0119]
    After cleaning, the reticle 210 is ready (and in position) for use in making a lithographic exposure.
  • [0120]
    Seventh Representative Embodiment
  • [0121]
    This embodiment is similar to the sixth representative embodiment, except for the inclusion of a separate cleaning-irradiation system 330 for reticle cleaning. The cleaning-irradiation system 330 is situated inside the process chamber 301. This embodiment is depicted in FIG. 11, in which all components that are the same as shown in FIG. 10 have the same reference numerals and are not described further.
  • [0122]
    After inspection, the reticle is moved to the right in FIG. 11 to a cleaning position (the reticle at the cleaning position has the reference numeral 210″). The cleaning-irradiation system 330 comprises an ion-beam source 331 and an ion-beam optical system 332. The reticle stage positions the reticle 210″, based on the data in the memory 325, such that an ion beam from the source 331 (and passing through the ion-beam optical system 332) is directed on the contaminant deposit. Suitable ion beams are of Ga ions, Si ions, or electrons. Meanwhile, the gas supply 310 discharges the reactive gas (and inert gas if desired) through the nozzle 314. Cleaning is performed as described above in the sixth representative embodiment. After cleaning is complete, the reticle 210 is moved to the exposure position between the illumination-optical system 303 and the projection-optical system 304.
  • [0123]
    Whereas the invention has been described in connection with multiple representative embodiments and examples, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention is intended to encompass all modifications, alternatives, and equivalents as may be included within the spirit and scope of the invention, as defined by the appended claims.
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Classifications
U.S. Classification134/1.3
International ClassificationB08B7/00
Cooperative ClassificationB08B7/0035
European ClassificationB08B7/00S
Legal Events
DateCodeEventDescription
Jan 9, 2002ASAssignment
Owner name: NIKON CORPORATION, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KAWATA, SHINTARO;OKADA, MASASHI;SHIMIZU, SUMITO;REEL/FRAME:012488/0039
Effective date: 20010913