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Publication numberUS20050112998 A1
Publication typeApplication
Application numberUS 10/974,736
Publication dateMay 26, 2005
Filing dateOct 28, 2004
Priority dateOct 30, 2003
Publication number10974736, 974736, US 2005/0112998 A1, US 2005/112998 A1, US 20050112998 A1, US 20050112998A1, US 2005112998 A1, US 2005112998A1, US-A1-20050112998, US-A1-2005112998, US2005/0112998A1, US2005/112998A1, US20050112998 A1, US20050112998A1, US2005112998 A1, US2005112998A1
InventorsHisanori Matsuo, Akira Ishikawa
Original AssigneeHisanori Matsuo, Akira Ishikawa
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Polishing apparatus
US 20050112998 A1
Abstract
A polishing apparatus is used for polishing a substrate such as a semiconductor wafer to a flat finish. The polishing apparatus includes a polishing tool having a polishing surface, a substrate holder configured to hold a substrate, a monitoring device configured to monitor a polishing state of the surface of the substrate being polished, and a controlling device configured to change a polishing condition on the basis of the polishing state of the surface of the substrate being polished detected by the monitoring device.
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Claims(15)
1. A polishing apparatus for polishing a substrate, comprising;
a polishing tool having a polishing surface;
a substrate holder configured to hold a substrate, the substrate held by said substrate holder being brought into sliding contact with said polishing surface;
a monitoring device configured to monitor a polishing state of the surface of the substrate being polished; and
a controlling device configured to change a polishing condition on the basis of said polishing state of the surface of the substrate being polished detected by said monitoring device.
2. A polishing apparatus according to claim 1, wherein said controlling device changes said polishing condition when said polishing state of the surface of the substrate being polished detected by said monitoring device becomes a preset condition related to peeling-off of a film formed on the substrate.
3. A polishing apparatus according to claim 2, wherein said film comprises a low-k film.
4. A polishing apparatus according to claim 1, wherein said monitoring device monitors at least one of a load torque of a motor for rotating said polishing tool and a load torque of motor for rotating said substrate holder.
5. A polishing apparatus according to claim 1, wherein said monitoring device monitors a force acting on said substrate holder in a sliding direction of said substrate holder.
6. A polishing apparatus according to claim 1, wherein said monitoring device monitors the state of the surface of the substrate being polished optically.
7. A polishing apparatus according to claim 1, wherein said monitoring device monitors whether acoustic emission is generated or not.
8. A polishing apparatus according to claim 1, wherein said polishing condition is a polishing load.
9. A polishing apparatus according to claim 1, wherein said polishing condition is at least one of a rotational speed of said polishing tool and a rotational speed of said substrate holder.
10. A polishing apparatus according to claim 1, wherein said polishing condition is a swing speed of said substrate holder.
11. A polishing apparatus according to claim 1, wherein said polishing condition is a supply amount of a polishing liquid supplied to said polishing surface.
12. A polishing apparatus according to claim 1, wherein said polishing condition is a type of polishing liquid.
13. A polishing apparatus according to claim 1, wherein said polishing condition is in-situ dressing condition.
14. A polishing apparatus according to claim 1, wherein said polishing condition is a temperature of a polishing liquid supplied to said polishing surface.
15. A polishing apparatus according to claim 1, wherein said polishing condition is a temperature of said polishing surface.
Description
    BACKGROUND OF THE INVENTION
  • [0001]
    1. Field of the Invention
  • [0002]
    The present invention relates to a polishing apparatus for polishing a substrate such as a semiconductor wafer to a flat finish.
  • [0003]
    2. Description of the Related Art
  • [0004]
    As telecommunication means such as Internet and high-speed large-capacity communication network have been remarkably developed, there has been an increasing demand for miniaturization and high integration in a semiconductor integrated circuit technology which supports the telecommunication means.
  • [0005]
    However, as a semiconductor device has become smaller in size and more highly integrated, an electric signal delay in the semiconductor device, i.e., RC delay has become a large problem. The RC delay is determined by the product of interconnect resistance R and interconnect capacitance C. Therefore, a countermeasure for preventing such RC delay is to use a combination of an interconnect metal having a low electric resistance and an interlayer dielectric/intermetal dielectric having a low dielectric constant.
  • [0006]
    Accordingly, instead of using tungsten (W), aluminum (Al), or aluminum alloys as a material for interconnects, there is a growing movement towards using copper (Cu) or copper alloys which have a lower electric resistance. Further, instead of Sio2, a low dielectric constant (i.e., low-k) material has been developed as a material for the interlayer dielectric/intermetal dielectric. In addition to the development of the low dielectric constant material, attempts have been made to lower a density of the film by introducing a porous structure into the material so that the dielectric constant of the interlayer dielectric/intermetal dielectric is further lowered.
  • [0007]
    Further, as a semiconductor device has become smaller in size and more highly integrated, structures of semiconductor elements have become more complicated. In addition, the number of layers in multilayer interconnects has been increased. Accordingly, irregularities on a surface of a semiconductor device become increased, and hence step heights on the surface of the semiconductor device tend to be larger. This is because, in a manufacturing process of a semiconductor device, a thin film is formed on a semiconductor device, then micromachining processes, such as patterning or forming holes, are performed on the semiconductor device, and these processes are repeated many times to form subsequent thin films on the semiconductor device.
  • [0008]
    When the number of irregularities on a surface of a semiconductor device is increased, a thickness of a thin film formed on a portion having a step tends to be small. Further, an open circuit is caused by disconnection of interconnects, or a short circuit is caused by insufficient insulation between interconnect layers. As a result, good products cannot be obtained, and the yield tends to be reduced. Furthermore, even if a semiconductor device initially works normally, reliability of the semiconductor device is lowered after a long-term use. At the time of exposure in a lithography process, if a surface to be irradiated has irregularities, then a lens unit in an exposure system cannot focus on such irregularities. Therefore, if the irregularities of the surface of the semiconductor device are increased, then it becomes difficult to form a fine pattern on the semiconductor device.
  • [0009]
    Accordingly, in a manufacturing process of a semiconductor device, it becomes increasingly important to planarize a surface of a semiconductor device. The most important one of the planarizing technologies is CMP (Chemical Mechanical Polishing). The chemical mechanical polishing is performed with use of a polishing apparatus. Specifically, a substrate such as a semiconductor wafer is brought into sliding contact with a polishing surface such as a polishing pad while a polishing liquid containing abrasive particles such as silica (SiO2) is supplied onto the polishing surface, so that the substrate is polished.
  • [0010]
    This type of polishing apparatus comprises a polishing table having a polishing surface constituted by a polishing pad or a fixed abrasive, and a substrate holder, called a top ring or a carrier head, for holding a substrate such as a semiconductor wafer. A substrate such as a semiconductor wafer is polished by the polishing apparatus in the following manner: The substrate is held by the substrate holder and then pressed against the polishing surface under a predetermined pressure. At this time, the polishing table and the substrate holder are moved relative to each other for thereby bringing the substrate into sliding contact with the polishing surface. Accordingly, the surface of the substrate is polished under a predetermined polishing pressure.
  • [0011]
    Generally, a low dielectric constant material has a low film adhesion strength. Therefore, in a case where the low dielectric constant material is used for the interlayer dielectric/intermetal dielectric, the following problems may arise in a polishing process:
      • (1) Separation (peeling-off) occurs at an interface between the interlayer dielectric/intermetal dielectric and a metal film or other films, resulting in failure of a fabrication process of a semiconductor device.
      • (2) In order to prevent such separation of the interlayer dielectric/intermetal dielectric, an excessively low polishing pressure is required in the polishing process, thus increasing a process time in a polishing process.
  • SUMMARY OF THE INVENTION
  • [0014]
    The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a polishing apparatus which can prevent a film formed on a substrate from being separated during a polishing process and can eliminate a need for selecting a process condition which may increase a process time in a polishing process.
  • [0015]
    In order to achieve the above object, according to the present invention, there is provided a polishing apparatus for polishing a substrate, comprising; a polishing tool having a polishing surface; a substrate holder configured to hold a substrate, the substrate held by the substrate holder being brought into sliding contact with the polishing surface; a monitoring device configured to monitor a polishing state of the surface of the substrate being polished; and a controlling device configured to change a polishing condition on the basis of the polishing state of the surface of the substrate being polished detected by the monitoring device.
  • [0016]
    According to the present invention, during polishing of the substrate, the polishing state of the surface of the substrate being polished is monitored by the monitoring device, and the polishing condition can be changed on the basis of the polishing state of the surface being polished which has been detected by the monitoring device. Therefore, even if a film composed of a material having a weak adhesion such as a low dielectric constant material is formed on the substrate, the polishing condition is changed by detecting the polishing state having a possibility of peeling-off of the film during polishing of the substrate, thus preventing the film from being peeled off.
  • [0017]
    According to one aspect of the present invention, the controlling device changes the polishing condition when the polishing state of the surface of the substrate being polished detected by the monitoring device becomes a preset condition related to peeling-off of a film formed on the substrate.
  • [0018]
    According to the present invention, as a preset condition related to peeling-off of a film, for example, a threshold value of a frictional force acting on the polishing interface is set, and when the frictional force which is being monitored during the polishing process exceeds the threshold value, operational commands are sent from the monitoring device to the controlling device, and then the process condition is controlled so that the frictional force is lowered by the controlling device. Thus, the film formed on the substrate can be prevented from being peeled off. Further, since the threshold value at which peeling-off of the film does not occur is determined in advance, and polishing of the substrate can be performed in such a condition that the frictional force approaches the threshold value as close as possible, the excessively safe process which takes long time to polish the substrate in order to prevent the film from being peeled off is not required to be selected.
  • [0019]
    According to one aspect of the present invention, the film comprises a low-k film.
  • [0020]
    According to one aspect of the present invention, the monitoring device monitors at least one of a load torque of a motor for rotating the polishing tool and a load torque of motor for rotating the substrate holder.
  • [0021]
    According to one aspect of the present invention, the monitoring device monitors a force acting on the substrate holder in a sliding direction of the substrate holder.
  • [0022]
    According to one aspect of the present invention, the monitoring device monitors the state of the surface of the substrate being polished optically.
  • [0023]
    According to one aspect of the present invention, the monitoring device monitors whether acoustic emission is generated or not.
  • [0024]
    According to one aspect of the present invention, the polishing condition is a polishing load.
  • [0025]
    According to one aspect of the present invention, the polishing condition is at least one of a rotational speed of the polishing tool and a rotational speed of the substrate holder.
  • [0026]
    According to one aspect of the present invention, the polishing condition is a swing speed of the substrate holder.
  • [0027]
    According to one aspect of the present invention, the polishing condition is a supply amount of a polishing liquid supplied to the polishing surface.
  • [0028]
    According to one aspect of the present invention, the polishing condition is a type of polishing liquid.
  • [0029]
    According to one aspect of the present invention, the polishing condition is in-situ dressing condition.
  • [0030]
    According to one aspect of the present invention, the polishing condition is a temperature of a polishing liquid supplied to the polishing surface.
  • [0031]
    According to one aspect of the present invention, the polishing condition is a temperature of the polishing surface.
  • [0032]
    According to the present invention, even if a material having a weak adhesion such as a low dielectric constant material is used for a film of a semiconductor device, the film formed on the substrate can be prevented from being peeled off during polishing of the substrate. Further, it is not necessary to select the excessively safe process which takes long time to polish the substrate in order to prevent the film from being peeled off. Thus, the process margin can be broadened.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0033]
    FIG. 1 is a schematic view showing an overall structure of a polishing apparatus according to an embodiment of the present invention;
  • [0034]
    FIG. 2 is a schematic view showing the polishing apparatus shown in FIG. 1, various sensors provided in the polishing apparatus, and a polishing-state monitoring and controlling apparatus;
  • [0035]
    FIG. 3 is a graph showing the pre-obtained data regarding the relationship between a load torque of a motor and a frictional force acting on a polishing interface;
  • [0036]
    FIG. 4 is a graph showing the pre-obtained data regarding the relationship between reflectivity of light and a surface of a substrate being polished;
  • [0037]
    FIG. 5 is a graph showing the relationship between a supply amount of a polishing liquid and a frictional force; and
  • [0038]
    FIG. 6 is a graph showing the relationship between types of polishing liquid and frictional coefficients.
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • [0039]
    A polishing apparatus according to embodiments of the present invention will be described below with reference to drawings.
  • [0040]
    FIG. 1 is a schematic view showing an overall structure of a polishing apparatus according to an embodiment of the present invention. As shown in FIG. 1, the polishing apparatus according to the present invention comprises a polishing table 1 having a polishing surface, a substrate holder 5 for holding a substrate 4 such as a semiconductor wafer to be polished and pressing the substrate 4 against the polishing surface of the polishing table 1, and a dresser 25 for dressing the polishing surface of the polishing table 1. The substrate 4 to be polished has a lower surface comprising a low-k film which is an object to be polished. A material for forming the low-k film includes SiOC, F doped SiO2, HSQ, MSQ, BCB (Benzo Cyclo Butene), PAE (Poly Arylene Ethers), SiO2, SiOF, Polyimide, PSI (Polyimide siloxane), CVD-PI (CVD polyimide), PTFE (Polytetrafluoroethylene), PNT (Polynaphthalene), BCB (Benzo cyclo butane), a-C:F (fluorinated amorphous carbon), Palylene-N, Palylene-F, SOG-Siloxan, or a porous structural member made of one of these materials.
  • [0041]
    The polishing table 1 has an upper surface to which a polishing pad 2 is attached, and the upper surface of the polishing pad 2 constitutes the polishing surface. The polishing table 1 is rotatable by a polishing table drive motor 9. A polishing liquid supply nozzle 8 is provided above the polishing table 1, and a polishing liquid Q (slurry) is supplied onto the polishing pad 2 on the polishing table 1 from the polishing liquid supply nozzle 8.
  • [0042]
    Various types of polishing pads are available on the market. For example, some of these are SUBA800, IC-1000, and IC-1000/SUBA400 (two-layer cloth) manufactured by Rodel, Inc., and Surfin xxx-5 and Surfin 000 manufactured by Fujimi Inc. SUBA800, Surfin xxx-5, and Surfin 000 are non-woven fabrics bound by urethane resin, and IC-1000 is made of rigid foam polyurethane (single-layer). Foam polyurethane is porous and has a large number of fine recesses or holes formed in its surface.
  • [0043]
    Although the polishing pad serves as the polishing surface, the present invention is not limited to the above structure. For example, the polishing surface may be constituted by a fixed abrasive. The fixed abrasive is formed into a flat plate comprising abrasive particles fixed by a binder. With the fixed abrasive for polishing, the polishing process is performed by abrasive particles that are self-generated from the fixed abrasive. The fixed abrasive comprises abrasive particles, a binder, and pores. For example, cerium dioxide (CeO2) or silicon oxide (SiO2) or alumina (Al2O3) having an average particle diameter of 0.5 μm or less is used as an abrasive particle, and thermosetting resin such as epoxy resin or phenol resin or thermoplastic resin such as MBS resin or ABS resin is used as a binder. Such a fixed abrasive forms a harder polishing surface. The fixed abrasive includes not only the above plate-like fixed abrasive but also a fixed abrasive pad having a two-layer structure formed by a thin layer of a fixed abrasive and an elastic polishing pad attached to a lower surface of the thin layer of the fixed abrasive.
  • [0044]
    The above polishing table and the polishing pad constitute a polishing tool. Further, the above polishing table and the fixed abrasive constitute a polishing tool. Here, the polishing table comprises SuS (metal), Al2O2, SiC, or the like.
  • [0045]
    The substrate holder 5 comprises a holder body 6 for holding the upper surface of the substrate, and an annular retainer ring 7 fixed to the lower end of the holder body 6 for retaining an outer circumferential edge of the substrate. The holder body 6 is made of a material having high strength and rigidity, such as metal or ceramics. The retainer ring 7 is made of highly rigid synthetic resin, ceramics, or the like. The substrate holder 5 is connected to a substrate holder drive shaft 11 by a universal joint 10, and the substrate holder drive shaft 11 is coupled to a substrate holder air cylinder 13 fixed to a substrate holder head 12. The substrate holder air cylinder 13 operates to move the substrate holder drive shaft 11 vertically to thereby lift and lower the substrate holder 5 as a whole and to press the substrate holder 5 against the polishing table 1.
  • [0046]
    The substrate holder air cylinder 13 is connected to a compressed air source 22 via a fluid passage 21 and a regulator R. The regulator R can regulate a pressure of compressed air or the like which is supplied to the substrate holder air cylinder 13. Thus, it is possible to adjust a pressing force to press the polishing pad 2 with the substrate holder 5, and hence a polishing pressure applied to the substrate can be adjusted to a desired value.
  • [0047]
    The substrate holder drive shaft 11 is connected to a rotary sleeve 15 by a key (not shown). The rotary sleeve 15 has a timing pulley 16 fixedly disposed at a peripheral portion thereof. A substrate holder drive motor 17 is fixed to the substrate holder head 12, and the timing pulley 16 is coupled to a timing pulley 19 mounted on the substrate holder drive motor 17 via a timing belt 18. Therefore, when the substrate holder drive motor 17 is energized for rotation, the rotary sleeve 15 and the substrate holder drive shaft 11 are rotated in unison with each other via the timing pulley 19, the timing belt 18, and the timing pulley 16 to thereby rotate the substrate holder 5. The substrate holder head 12 is supported on a substrate holder head shaft 20 rotatably supported on a frame (not shown). The substrate holder head 12 is swingable by rotating the substrate holder head shaft 20 so that the substrate holder 5 is movable between a substrate transfer position for transferring the substrate and a polishing position on the polishing surface of the polishing table 1. The substrate holder 5 is swingable on the polishing surface of the polishing table 1 by rotating the substrate holder head shaft 20 in normal and reverse directions. Further, the swing speed of the substrate holder 5 is adjustable by the rotational speed of the substrate holder head shaft 20.
  • [0048]
    The dresser 25 comprises a diamond dresser having diamond particles electrodeposited thereon, for example. The dresser 25 is supported from a dresser head 27 by a dresser drive shaft 26. The dresser drive shaft 26 is coupled to a dresser drive motor 28, and the dresser 25 is rotated by a dresser drive motor 28. The dresser head 27 is supported on a dresser head shaft 29 rotatably supported on a frame (not shown). The dresser head 27 is swingable by rotating the dresser head shaft 29 so that the dresser 25 is movable between a standby position and a dressing position on the polishing surface of the polishing table.
  • [0049]
    Overall operation of the polishing apparatus shown in FIG. 1 will be described below.
  • [0050]
    In the polishing apparatus having the above structure, when the substrate 4 such as a semiconductor wafer is to be supplied to the top ring 1, the substrate holder 5 is placed in its entirety into the substrate transfer position. Then, the substrate 4 is transferred to the substrate holder 5 by a substrate transfer apparatus (pusher) provided at the substrate transfer position, and the substrate 4 is held on the lower end surface of the substrate holder 5 under vacuum. Next, the substrate holder 5 holding the substrate 4 under vacuum is moved in its entirety to a position above the polishing table 1. The outer circumferential edge of the substrate 4 is retained by the retainer ring 7 so that the substrate 4 will not be dislodged from the substrate holder 5.
  • [0051]
    Then, the attraction of the substrate 4 is released. At the same time, the substrate holder air cylinder 13 connected to the substrate holder drive shaft 11 is operated to press the substrate 4 held by the lower end surface of the substrate holder 5 against the polishing pad 2 of the polishing table 1. At this time, the polishing table 1 and the substrate holder 5 are being rotated by the polishing table drive motor 9 and the substrate holder drive motor 17 at respective desired rotational speeds. The polishing liquid Q which has been supplied from the polishing liquid supply nozzle 8 is retained on the polishing pad 2. The substrate 4 is now polished with the polishing liquid Q being present between the surface (lower surface) of the substrate 4 and the polishing pad 2. By regulating a pressure of air supplied to the substrate holder air cylinder 13, a polishing pressure applied to the substrate can be adjusted to a desired value. During polishing of the substrate 4, a polishing state of the surface of the substrate 4 being polished is monitored, and is controlled. At the same time that the substrate is polished, the dresser 25 is rotated at a predetermined rotational speed while the dresser 25 is pressed against the polishing pad 2 and the dressing liquid is supplied to the polishing pad 2. Thus, in-situ dressing of the polishing pad 2 is performed.
  • [0052]
    Next, a polishing state monitoring and controlling apparatus for monitoring a polishing state of the substrate and controlling the polishing state of the substrate during a polishing process will be described with reference to FIGS. 2 through 6.
  • [0053]
    FIG. 2 is a schematic view showing the polishing apparatus shown in FIG. 1, various sensors provided in the polishing apparatus, and a polishing state monitoring and controlling apparatus. As shown in FIG. 2, the polishing apparatus has a polishing state monitoring and controlling apparatus 30, and the polishing state monitoring and controlling apparatus 30 comprises a polishing state monitoring unit 31 and a polishing state controlling unit 32. The polishing state monitoring unit 31 constitutes a monitoring device configured to monitor a polishing state of the surface of the substrate being polished, and the polishing state controlling unit 32 constitutes a controlling device configured to change a polishing condition on the basis of the polishing state of the surface of the substrate being polished detected by the monitoring device (described later). A motor torque of the polishing table drive motor 9 for rotating the polishing table 1 is detected on the basis of a motor current value, and the detected motor torque is inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30. A motor torque of the substrate holder drive motor 17 for rotating the substrate holder 5 is detected on the basis of a motor current value, and the detected motor torque is inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30.
  • [0054]
    A force sensor 33 for detecting an acting force is provided on the substrate holder 5, and a force acting on the substrate holder 5 in the sliding direction of the substrate holder 5 is detected by the force sensor 33. Then, the detected acting force is inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30. Further, an acoustic emission sensor (AE sensor) 35 is provided on the substrate holder 5, and elastic wave (described later on) detected by the acoustic emission sensor 35 is inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30.
  • [0055]
    On the other hand, an optical sensor 34 is provided in the polishing table 1, and reflected light from the substrate 4 detected by the optical sensor 34 is inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30. The optical sensor 34 comprises a light-emitting element and a light-receiving element. Light for measurement from the light-emitting element is applied to the substrate 4, and reflected light from the substrate 4 is received by the light-receiving element. This received reflected light is inputted into the polishing state monitoring unit 31, as described above.
  • [0056]
    Next, operation of the various sensors and the polishing state monitoring and controlling apparatus constructed as shown in FIG. 2 will be described below.
  • [0057]
    The respective torque values of the polishing table drive motor 9 and the substrate holder drive motor 17 are inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30. In the polishing state monitoring unit 31, a frictional force acting between the surface of the substrate 4 and the polishing surface of the polishing pad 2 on the polishing table 1 is detected from the torque of the polishing table drive motor 9 and/or the torque of the substrate holder drive motor 17. In this case, the relationship between the frictional force acting on the polishing interface between the surface of the substrate 4 and the polishing surface of the polishing pad 2 on the polishing table 1, and the load torque (torque of the motor) are determined in advance.
  • [0058]
    FIG. 3 is a graph showing the pre-obtained data regarding the relationship between a load torque of a motor and a frictional force acting on a polishing interface. In FIG. 3, the horizontal axis represents a load torque of the motor, and the vertical axis represents a frictional force acting on the polishing interface. As shown in FIG. 3, there is linear correlation between the load torque of the motor and the frictional force.
  • [0059]
    As shown in FIG. 3, the frictional force acting between the surface of the substrate 4 being polished and the polishing surface of the polishing pad 2 on the polishing table 1 is detected from a torque of the polishing table drive motor 9 and/or a torque of the substrate holder drive motor 17 on the basis of the pre-obtained data regarding the relationship between the load torque of the motor and the frictional force acting on the polishing interface. In this manner, the detected frictional force acting on the polishing interface between the surface of the substrate 4 being polished and the polishing surface of the polishing pad 2 on the polishing table 1 is monitored at all times during a polishing process by the polishing state monitoring unit 31.
  • [0060]
    The force sensor 33 provided on the substrate holder 5 comprises an acceleration sensor, and the frictional force acting on the polishing interface between the surface of the substrate 4 being polished and the polishing surface of the polishing pad 2 can be detected on the basis of an acceleration (vibration) detected by the force sensor 33. In this case, in the polishing state monitoring unit 31, frequency components having a strong correlation with the polishing process are extracted from signals inputted from the force sensor 33 into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30, and the time variation of the extracted frequency components is monitored. The relationship between a vibration strength and a frictional force acting on the polishing interface between the surface of the substrate 4 being polished and the polishing surface of the polishing pad 2 is determined in advance.
  • [0061]
    Further, in the optical sensor 34, visible light is applied to the surface of the substrate 4 being polished by the light-emitting element, and reflected light from the surface of the substrate 4 being polished is received by the light-receiving element. Then, the reflected light is inputted into the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30, and reflectivity of light can be detected. In the polishing state monitoring unit 31, during the polishing process, the state of the surface of the substrate 4 being polished can be optically monitored by monitoring the reflectivity of light.
  • [0062]
    FIG. 4 is a graph showing the pre-obtained data regarding the relationship between reflectivity of light and a surface of a substrate being polished. In FIG. 4, the horizontal axis represents time (seconds), and the vertical axis represents reflectivity of light (%) of a surface of a substrate being polished. As shown in FIG. 4, the reflectivity (%) varies rapidly after a lapse of about 30 seconds, and thereafter the reflectivity is rapidly lowered. In this case, this is because peeling-off of a film occurs after a lapse of about 30 seconds. By monitoring the reflectivity of light of the surface of the substrate 4 being polished, generation of peeling-off of the film formed on the substrate 4 can be detected.
  • [0063]
    When the film of the surface of the substrate 4 being polished is peeled off, elastic wave in an ultrasonic band is emitted, and this phenomenon is called acoustic emission. Therefore, the acoustic emission sensor 35 provided on the substrate holder 5 detects this elastic wave to detect peeling-off of the film. In the polishing state monitoring unit 31, during the polishing process, whether the acoustic emission (AE) is generated or not is monitored, whereby peeling-off of the film generated in the surface of the substrate 4 being polished is monitored.
  • [0064]
    In this manner, various values including the torque of the motor, the vibration strength, the reflectivity of light, the AE, and the like are monitored at all times during the polishing process in the polishing state monitoring unit 31 of the polishing state monitoring and controlling apparatus 30. In this case, in the polishing state monitoring unit 31, measured values such as torques, vibration strength, reflectivity of light, and the like are compared with predetermined threshold values at all times during the polishing process.
  • [0065]
    The above threshold values are determined in the following procedure, for example.
    • (1) A critical frictional force at which peeling-off of a film of a substrate to be polished occurs is determined in advance.
    • (2) A threshold value of the frictional force which can be applied to the substrate during the polishing process is determined in consideration of safety factor.
  • [0068]
    The above determined threshold value is used, and when the frictional force of the polishing interface which is being monitored exceeds the determined threshold value, operational commands are sent from the polishing state monitoring unit 31 to the polishing state controlling unit 32, and the process condition is controlled so that the frictional force is lowered by the polishing state controlling unit 32. Specifically, the polishing load is lowered, the flow rate of the polishing liquid (slurry) is reduced, the rotational speed of the substrate holder 5 and/or the polishing table 1 is lowered, the type of polishing liquid (slurry) is changed, or other controls may be performed.
  • [0069]
    As described above, when the measured value which is being monitored exceeds the threshold value, the operational commands are sent form the polishing state monitoring unit 31 to the polishing state controlling unit 32. Then, as shown in FIG. 2, control of the polishing load, control of the rotational speed of the polishing table 1 and/or the substrate holder 5, control of the supply amount of the polishing liquid, control of the in-situ dressing condition, control of the temperature of the polishing liquid, control of the temperature of the polishing surface, and change of the type of polishing liquid are performed. In this case, of these kinds of control, one or more kinds of control are suitably combined to prevent the film formed on the substrate 4 from being peeled off. The control of the temperature of the polishing liquid is performed by a temperature adjustment device such as a heater or a chiller for heating or cooling the polishing liquid. Further, a control method of controlling the temperature of the polishing surface includes a method of allowing a temperature regulating fluid to flow from the backside surface of the polishing table, a method of warming the polishing surface by applying light to the polishing surface, and a method of cooling the polishing surface by ventilation.
  • [0070]
    FIG. 5 is a graph showing the relationship between a supply amount of a polishing liquid and a frictional force, and the horizontal axis represent a flow rate of the polishing liquid (ml/min) and the vertical axis represents a frictional force of a polishing interface (N).
  • [0071]
    As shown in FIG. 5, the frictional force of the polishing interface can be lowered by reducing the supply amount of the polishing liquid. Therefore, when the frictional force which is being monitored exceeds a threshold value, the frictional force is lowered by reducing the supply amount of the polishing liquid. Thus, the film formed on the substrate 4 can be prevented from being peeled off.
  • [0072]
    FIG. 6 is a graph showing the relationship between types of polishing liquid and frictional coefficients, and the horizontal axis represents types of polishing liquid and the vertical axis represents frictional coefficients. In FIG. 6, Ox-1 is silicon-dioxide-film polishing slurry SS-25 manufactured by Cabot Corporation, Cu-1 is copper-film polishing slurry PL7101 manufactured by Fujimi Incorporated, Cu-2 is copper-film polishing slurry CMS7303/7304 manufactured by JSR Corporation, Cu-3 is copper-film polishing slurry PL7102/DCM-G2 manufactured by Fujimi Incorporated, Cu-4 is abrasive particle-free copper-film polishing slurry l, and Cu-5 is abrasive particle-free copper-film polishing slurry 2. Further, Ta-1 is barrier-metal polishing slurry B-12 manufactured by Fujimi Incorporated, and Ta-2 is barrier-metal polishing slurry CMS8301 manufactured by JSR Corporation.
  • [0073]
    As is apparent from FIG. 6, the frictional force of the polishing interface can be lowered by changing the type of polishing liquid. Therefore, when the frictional force of the polishing interface which is being monitored exceeds the threshold value, the frictional force is lowered by changing the type of polishing liquid. Thus, the film formed on the substrate 4 can be prevented from being peeled off.
  • [0074]
    A plurality of threshold values can be determined, and the optimum process can be maintained by determining a lower limit and an upper limit of the threshold values. The optimum process condition means that the frictional force of the polishing interface is as small as possible and the polishing rate is as large as possible. However, it is necessary to consider within wafer non-uniformity of the surface of the substrate to be polished or the pattern characteristics. Basically, the larger the frictional force is, the higher the polishing rate is. Therefore, the optimum process condition may be such a condition that the frictional force approaches the above threshold value as close as possible. Specifically, while the frictional force of the polishing interface is monitored by the polishing state monitoring unit 31, if the frictional force is lowered excessively, then the polishing apparatus is operated such that parameters are controlled so as to increase the frictional force.
  • [0075]
    Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
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Classifications
U.S. Classification451/5, 451/8, 451/7
International ClassificationB24B37/07, B24B49/10, B24B49/16, H01L21/304, B24B49/12
Cooperative ClassificationB24B49/12, B24B37/013
European ClassificationB24B37/013, B24B49/12
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Effective date: 20041101
Owner name: NIKON CORPORATION, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MATSUO, HISANORI;ISHIKAWA, AKIRA;REEL/FRAME:016193/0960
Effective date: 20041101