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MODULATING ION BEAM CURRENT
FIELD OF THE INVENTION
The present invention relates generally to ion implanta- 5 tion systems, and more particularly to modulating ion beam current in such systems to attain more uniform ion implantations.
BACKGROUND OF THE INVENTION 10
Ion implantation systems are used to impart impurities, known as dopant elements, into semiconductor substrates or wafers, commonly referred to as workpieces. In such systems, an ion source ionizes a desired dopant element, and the 15 ionized impurity is extracted from the ion source as a beam of ions. The ion beam is directed (e.g., swept) across respective workpieces to implant ionized dopants within the workpieces. The dopant ions alter the composition of the workpieces causing them to possess desired electrical char- 20 acteristics, such a may be useful for fashioning particular semiconductor devices, such as transistors, upon the substrates.
The continuing trend toward smaller electronic devices has presented an incentive to "pack" a greater number of 25 smaller, more powerful and more energy efficient semiconductor devices onto individual wafers. This necessitates careful control over semiconductor fabrication processes, including ion implantation and more particularly the uniformity of ions implanted into the wafers. Moreover, semicon- 30 ductor devices are being fabricated upon larger workpieces to increase product yield. For example, wafers having a diameter of 300 mm or more are being utilized so that more devices can be produced on a single wafer. Such wafers are expensive and, thus, make it very desirable to mitigate 35 waste, such as having to scrap an entire wafer due to non-uniform ion implantation. Larger wafers make uniform ion implantation challenging, however, since ion beams have to be scanned across larger angles and distances to reach the perimeters of the wafers. Scanning a beam over 40 such larger angles and distances can cause variations in the flux of the beam that can lead to non-uniform implantation.
SUMMARY OF THE INVENTION
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. 50 Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention is directed to modulating ion beam 55 current in an ion implantation system to mitigate nonuniform ion implantations, for example. Multiple arrangements are disclosed for modulating the intensity of the ion beam. For example, the volume or number of ions within the beam is altered by biasing one or more different elements 60 downstream of the ion source. Similarly, the dosage of ions within the ion beam can also be manipulated by controlling elements more closely associated with the ion source. In this manner, the implantation process can be regulated so that the wafer is coated with a more uniform concentration of ions. 65
According to one or more aspects of the present invention, an ion implantation system suitable for use in implanting
ions into one or more workpieces is disclosed. The system includes an ion source for producing a quantity of ions that can be extracted in the form of an ion beam having a beam current. The system also includes a beamline assembly downstream of the ion source to receive and direct the beam of ions. An end station downstream of the beamline assembly is also included to hold the one or more workpieces toward which the ion beam is directed. Finally, the system includes a component associated with or downstream of the ion source for modulating the ion beam current.
In accordance with one or more other aspects of the present invention, an acceleration system suitable for use in implanting ions into a workpiece is disclosed. The system includes an ion source for producing a quantity of ions that can be extracted in the form of an ion beam, the ion beam having a beam current. The system also includes a beamline assembly downstream of the ion source to receive and direct the beam of ions. An end station downstream of the beamline assembly is also included to hold one or more workpieces onto which the ion beam is directed. Finally, the system includes a first modulating component associated with the ion source for modulating the beam current.
To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram illustrating components of an ion implantation system according to one or more aspects of the present invention to modulate ion beam current.
FIG. 2 is a cross sectional side view illustrating an exemplary ion implantation system in accordance with one or more aspects of the present invention.
FIG. 3 is a schematic block diagram illustrating particular components of an ion implantation system wherein one or more aspects of the present invention are implemented;
FIG. 4 is a top view of an ion implantation system wherein one or more aspects of the present invention are implemented to modulate ion beam current;
FIG. 5 is a graphical representation depicting a relationship between changes in an extraction suppression voltage and changes in ion beam current; and
FIG. 6 is another graphical representation illustrating a relationship between changes in an extraction suppression voltage and changes in ion beam current.
DETAILED DESCRIPTION OF THE
The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout. The illustrations and following descriptions are exemplary in nature, and not limiting. Thus, it will be appreciated that variants of the illustrated systems and methods and other such implementations apart from those illustrated herein are deemed as falling within the scope of the present invention and the appended claims.
The present invention relates to modulating ion beam current in an ion implantation system to mitigate nonuniform ion implantations, for example. Multiple arrangements are revealed for modulating the intensity of the ion beam. For example, the volume or number of ions within the 5 beam is altered by biasing one or more different elements downstream of the ion source. Alternatively, the dosage of ions within the ion beam can also be manipulated by controlling elements more closely associated with the ion source. In this manner, the implantation process can be 10 regulated so that the concentration of ions implanted into the wafer is substantially uniform across the wafer.
Referring initially to FIG. 1, an ion implantation system 100 suitable for implementing one or more aspects of the present invention is depicted in block diagram form. The 15 system 100 includes an ion source 102 for producing a quantity of ions that can be extracted in the form of an ion beam 104. The ion source 102 generally includes a gas source 106 from which the ions are generated, and a power source 108 that facilitates the production of the ions from the 20 gas.
Abeamline assembly 110 is provided downstream of the ion source 102 to receive the ion beam 104. The beamline assembly 110 in one example includes, among other things, a mass analyzer 112. The beamline assembly 110 is situated 25 along the path to receive the beam 104. The mass analyzer 112 includes a field generating component, such as a magnet 114, and operates to provide a field across the beam path 104 so as to deflect ions from the ion beam 104 at varying trajectories according to mass (e.g., charge to mass ratio). 30 Ions traveling through the magnetic field experience a force that directs individual ions of a desired mass along the beam path 104 and deflects ions of undesired mass away from the beam path.
The ion implantation system 100 further includes an end 35 station 116 to receive the mass analyzed ion beam 104 from the beamline assembly 110. The end station 116 supports one or more workpieces such as semiconductor wafers (not shown) along the beam path for implantation using the mass analyzed ion beam 104. The end station 116 includes a target 40 scanning system 118 for translating or scanning one or more target workpieces and the ion beam 104 relative to one another. The target scanning system 118 may provide for batch or serial implantation, for example, as may be desired under given circumstances, operating parameters and/or 45 objectives.
Additionally, a measurement component 120 is operatively coupled to the end station 116. The measurement component may include, for example, a Faraday cup (not shown) that is operable to detect the intensity of the ion 50 beam as the beam is scanned across the wafer. According to one or more aspects of the present invention, the detected current density is fed back (e.g., via a processor—not shown) to control one or more beam current modulation components 122, 124. In accordance with one or more 55 aspects of the present invention, one or more of the components 122, 124 can be closely associated with the ion source 102 and/or be situated downstream from the ion source 102 (e.g., on the beamline assembly 110 or end station 116). 60
The ion implantation system 100 may also include a mechanism 126 in front of the end station 116 to scan the ion beam 104 relative to the one or more workpieces. Such mechanisms may, for example, be electric and/or magnetic. For example, the mechanism may include one or more 65 electrically conductive plates that can be biased to have an electromagnetic field controllably developed there-across.
The field lines influence the direction of the ion beam 104 passing there-through, and can be selectively controlled to cause the beam 104 to scan across the workpieces in a desired manner.
Referring now to FIG. 2, an exemplary ion implantation system 200 suitable for implementing one or more aspects of the present invention is depicted in somewhat greater detail. Note that although the system in FIG. 2 illustrates a low energy system, it should be appreciated that the system 200 is provided as an example, and that the present invention finds utility in various types of ion implantation systems, and such variations are contemplated as falling within the scope of the present invention. The system 200 includes an ion source 202, a beamline assembly 204, and a target or end station 206. An expansible stainless steel bellows assembly 208, which permits movement of the end station 206 with respect to the beamline assembly 204, connects the end station 206 and the beamline assembly 204.
The ion source 202 comprises a plasma chamber 210 and an ion extraction assembly 212. Energy is imparted to an ionizable dopant gas to generate ions within the plasma chamber 210. Generally, positive ions are generated, although the present invention is applicable to systems wherein negative ions are generated by the source 202. The positive ions are extracted through a slit in the plasma chamber 210 by the ion extraction assembly 212, which comprises a plurality of electrodes 214. Accordingly, the ion extraction assembly 212 functions to extract a beam 216 of positive ions from the plasma chamber 210 and to accelerate the extracted ions into the beamline assembly 204, and more particularly into a mass analysis magnet 218 within the beamline assembly 204.
The mass analysis magnet 218 includes a curved beam path 220 within a passageway 222 defined by a metal (e.g., aluminum) beam guide having side-walls 224, evacuation of which is provided by a vacuum pump 226. The ion beam 216 that propagates along this path 220 is affected by the magnetic field generated by the mass analysis magnet 218, to reject ions of an inappropriate charge-to-mass ratio. Control electronics 228 are included to adjust the strength and orientation of this dipole magnetic field, among other things. The magnetic field is controlled by the electrical current through the field windings of the magnet 218 through a magnet connector 230. It will be appreciated that control electronics 228 may include a processor and/or computer system for overall control of the system 200 (e.g., by an operator).
The dipole magnetic field causes the ion beam 216 to move along the curved beam path 220 from a first or entrance trajectory 232 near the ion source 202 to a second or exit trajectory 234 near an exiting end of the passageway 222. Portions 236 and 238 of the beam 216, comprised of ions having an inappropriate charge-to-mass ratio, are deflected away from the curved trajectory and into the beam guide side walls 224. In this manner, the magnet 218 only allows those ions in the beam 220 which have the desired charge-to-mass ratio to traverse entirely through the passageway 222.
The beamline assembly 204 can also be said to include an accelerator 240. The accelerator 240 includes a plurality of electrodes 242 arranged and biased to accelerate and/or decelerate ions, as well as to focus, bend and decontaminate the ion beam. A dosimetry indicator such as a Faraday cup 244 may also be included to detect a sample current of the ion beam. A source of plasma 246 may also be included to provide a plasma shower 248 for neutralizing a (positive) charge that would otherwise accumulate on a target work