Variable thickness ion source extraction plate

Abstract

An ion source is disclosed having an extraction plate of variable thickness. The extraction plate has a protrusion on its inner or outer surface adjacent to the extraction aperture. The protrusion increases the thickness of the extraction aperture in certain regions. This increases the loss area in these regions, which acts as a sink for ions and electrons. In this manner, the plasma density is reduced more in regions where the extraction aperture is thicker. The shape of the protrusion may be modified to achieve a desired plasma uniformity. Thus, it may be possible to generate an extracted ion beam with a more uniform ion density. In some tests, the beam current uniformity along the width direction has been improved by 20% to 50%.

Description

Technical Field

[0001] This application claims the benefit of priority to U.S. Patent Application No. 17 / 473,096, filed Sep. 13, 2021, the disclosure of which is incorporated herein by reference in its entirety.

[0002] This disclosure describes a system for improving the uniformity of a ribbon ion beam extracted from an ion source, particularly from an indirectly heated cathode (IHC) ion source.

Background Art

[0003] Semiconductor devices are manufactured using multiple processes. Some of those processes involve implanting ions into a workpiece. Various ion sources can be used to generate the ions. One such mechanism is an indirectly heated cathode (IHC) ion source. The IHC ion source includes a filament disposed behind the cathode. The cathode can be maintained at a voltage that is positive relative to the filament. Passing a current through the filament emits thermoelectrons from the filament, and those thermoelectrons are accelerated toward the more positively charged cathode. These thermoelectrons help heat the cathode, which then emits electrons into the ion source chamber. The cathode is disposed at one end of the chamber. A repeller is typically disposed at the end of the chamber opposite the cathode.

[0004] In certain embodiments, the ion source is configured to extract a ribbon ion beam. The width of the ribbon ion beam is significantly larger than the height of the ribbon ion beam. Unfortunately, in many systems, the beam current of the extracted ribbon ion beam is not uniform along its width. This non-uniformity can cause the concentration of ions implanted into the workpiece to be non-uniform. In other embodiments, additional components within the beamline, such as quadrupole lenses, may be utilized in an attempt to compensate for this non-uniformity. These measures can add additional complexity and cost to the beamline system.

[0005] Therefore, it would be beneficial to have a system that can improve the uniformity of the ribbon ion beam extracted from the ion source. Further, it would be advantageous if this system could be easily adopted for existing ion sources. SUMMARY OF THE INVENTION

[0006] An ion source having an extraction plate with variable thickness is disclosed. The extraction plate has protrusions on its inner or outer surface proximate to the extraction aperture. These protrusions increase the thickness of the extraction aperture within a specific region. This increases the loss area in these regions, which functions as a sink for ions and electrons. In this way, the plasma density decreases more significantly in regions where the thickness of the extraction aperture is greater. The shape of the protrusions may be altered to achieve the desired plasma uniformity. Therefore, it may be possible to generate an extracted ion beam with a more uniform ion density. In some tests, the uniformity of the beam current along the width direction was improved by 20% to 50%.

[0007] According to one embodiment, an ion source is disclosed. The ion source includes a chamber having a first end, a second end, and a plurality of walls connecting the first end and the second end. One of the plurality of walls is an extraction plate having an extraction opening with a width greater than its height. The ion source further includes a plasma generator for generating plasma within the chamber. The thickness of the extraction opening varies as a function of the width of the extraction opening. In some embodiments, the extraction plate includes a protrusion for varying the thickness of the extraction opening. In certain embodiments, the protrusion extends at least 1 mm into the chamber from the inner surface of the extraction plate at at least one location. In certain embodiments, the protrusion extends at least 1 mm outward from the outer surface of the extraction plate at at least one location. In some embodiments, the protrusion has a constant radius of curvature from the first end to the second end. In some embodiments, the protrusion has a triangular shape. In some embodiments, the protrusion has a trapezoidal shape. In certain embodiments, the maximum thickness of the protrusion occurs at the center of the extraction opening in the width direction. In some embodiments, the extraction opening passes through the protrusion and the edges of the extraction opening taper in the height direction. Thereby, the height of the extraction opening inside the chamber is greater than the height of the extraction opening on the outer surface of the extraction plate. In certain embodiments, the extraction opening passes through the protrusion and the edges of the extraction opening are as follows. That is, the height of the extraction opening inside the chamber is equal to the height of the extraction opening on the outer surface of the extraction plate. In some embodiments, the protrusion above the extraction opening in the height direction has a different thickness from the protrusion below the extraction opening in the height direction. In some embodiments, the protrusion is disposed only on one side of the extraction opening in the height direction. In some embodiments, the plasma generator includes an indirectly heated cathode disposed at the first end.

[0008] According to another embodiment, an extraction plate for use with an ion source is disclosed. The extraction plate has an inner surface, an outer surface adapted within a chamber, and an extraction aperture having a width greater than its height. The thickness of the extraction aperture varies as a function of the width of the extraction aperture. In certain embodiments, the extraction plate comprises protrusions on the inner surface or the outer surface. In certain embodiments, the maximum thickness of the protrusion occurs at the center of the extraction aperture in the width direction. In some embodiments, the extraction aperture penetrates the protrusion and the edges of the extraction aperture taper in the height direction. Thereby, the height of the extraction aperture inside the chamber is greater than the height of the extraction aperture on the outer surface of the extraction plate. In some embodiments, the extraction aperture penetrates the protrusion and the edges of the extraction aperture are as follows. That is, the height of the extraction aperture inside the chamber is equal to the height of the extraction aperture on the outer surface of the extraction plate.

[0009] In some embodiments, the protrusion above the extraction aperture in the height direction has a different thickness from the protrusion below the extraction aperture in the height direction. In certain embodiments, the protrusion is disposed only on one side of the extraction aperture in the height direction.

[0010] To better understand the present disclosure, reference is made to the accompanying drawings. In the accompanying drawings, like elements are referred to with like numerals.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 3D

Figure 3E

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 shows an IHC ion source 10 that can be used to extract a ribbon ion beam having improved uniformity. The IHC ion source 10 includes a chamber 100 having two opposing ends and a wall 101 connecting these ends. These walls 101 include side walls, namely, an extraction plate 103 and a bottom wall opposing the extraction plate 103. The extraction plate 103 has a height, a width, and a thickness. The extraction plate 103 includes an extraction opening 140 that penetrates the extraction plate 103 in the thickness direction. Ions are extracted through the extraction opening 140. The extraction opening 140 may be considerably larger in the width direction (also called the X - direction) than in the height direction (also called the Y - direction). The Z - direction is defined along the thickness of the extraction plate 103 and is defined as the moving direction of the ribbon ion beam. For example, the extraction opening 140 may be larger than 3 inches in the width direction and smaller than 0.3 inches in the height direction.

[0013] The wall 101 of the chamber 100 may be constructed of a conductive material and may be electrically connected to each other. The cathode 110 is disposed within the chamber 100 at the first end 104 of the chamber 100. The filament 160 is disposed behind the cathode 110. The filament 160 is in communication with a filament power supply 165. The filament power supply 165 is configured to pass a current through the filament 160. Thereby, the filament 160 emits thermoelectrons. A cathode bias power supply 115 biases the filament 160 negatively with respect to the cathode 110. Accordingly, these thermoelectrons are accelerated from the filament 160 toward the cathode 110, and when these thermoelectrons hit the back surface of the cathode 110, the cathode 110 is heated. The cathode bias power supply 115 may bias the filament 160 to have a voltage, for example, between -200 V and -1500 V relative to the voltage of the cathode 110. Then, the cathode 110 emits thermoelectrons into the chamber 100 from its front surface.

[0014] Accordingly, the filament power supply 165 supplies a current to the filament 160. The cathode bias power supply 115 biases the filament 160. Thereby, the filament 160 becomes more negative than the cathode 110. As a result, electrons are attracted from the filament 160 toward the cathode 110. The cathode 110 is in communication with an arc voltage power supply 111. The arc voltage power supply 111 supplies a voltage to the cathode with respect to the chamber 100. This arc voltage accelerates the thermoelectrons emitted from the cathode into the chamber 100 to ionize the neutral gas. The current drawn by this arc voltage power supply 111 is a measured value of the amount of current driven through the plasma. In certain embodiments, the wall 101 serves as a ground reference for other power supplies.

[0015] In this embodiment, the reflective electrode 120 is disposed within the chamber 100 at the second end 105 of the chamber 100 opposite the cathode 110. The center of the cathode 110 and the center of the reflective electrode 120 may form two points on the central axis 109 of the chamber 100.

[0016] The reflective electrode 120 may be electrically connected to the reflective electrode power supply 123. As its name indicates, the reflective electrode 120 serves to repel the electrons emitted from the cathode 110 toward the center of the chamber 100. For example, in certain embodiments, the reflective electrode 120 may be biased to a negative voltage with respect to the chamber 100 in order to repel electrons. For example, in certain embodiments, the reflective electrode 120 is biased between 0 and -150 V with respect to the chamber 100. In certain embodiments, the reflective electrode 120 may be in a floating state with respect to the chamber 100. In other words, when the reflective electrode 120 is in a floating state, it is not electrically connected to either the reflective electrode power supply 123 or the chamber 100. In this embodiment, the voltage of the reflective electrode 120 tends to drift to a voltage close to the voltage of the cathode 110. Alternatively, the reflective electrode 120 may be electrically connected to the wall 101.

[0017] In certain embodiments, a magnetic field 190 is generated within the chamber 100. This magnetic field is intended to confine the electrons along one direction. The magnetic field 190 typically passes parallel to the wall 101 from the first end 104 to the second end 105. For example, the electrons may be confined within a column parallel to the direction from the cathode 110 to the reflective electrode 120 (i.e., the X direction). Thus, the electrons do not receive an electromagnetic force moving in the X direction. However, the movement of electrons in other directions may be subject to an electromagnetic force.

[0018] One or more gas containers 108 may communicate with the chamber 100 via the gas inlet 106. Each gas container 108 may include a mass flow controller (MFC) to regulate the gas flow from each gas container.

[0019] The extraction power supply 170 can be used to bias the wall 101 of the IHC ion source 10 with respect to the remaining components within the beam line. For example, the platen 260 (see FIG. 2) may be at a first voltage such as ground, while a positive voltage is applied to the IHC ion source 10 such that the IHC ion source 10 is biased more positively than the platen 260. Thus, the voltage supplied by the extraction power supply 170, referred to as the extraction voltage, determines the energy of the ions extracted from the IHC ion source 10. Further, the current supplied by the extraction power supply 170 serves as a measure of the total extraction beam current.

[0020] In certain embodiments, there is a feedback loop between the cathode bias power supply 115 and the extraction power supply 170. Specifically, it may be desirable to maintain the extraction beam current at a constant value. Thus, the current supplied by the extraction power supply 170 may be monitored, and the output of the cathode bias power supply 115 can be adjusted to maintain a constant extraction current. This feedback loop may be implemented by the controller 180 or in another manner.

[0021] Controller 180 may be in communication with one or more of the power supplies. Thereby, the voltage or current supplied by these power supplies may be monitored and / or corrected. Further, controller 180 may be in communication with the MFCs of each gas container 108 to regulate the flow of each gas into chamber 100. Controller 180 may include a processing unit such as a microcontroller, a personal computer, a dedicated controller, or another suitable processing unit. Controller 180 may also include a non-transitory storage element such as a semiconductor memory, a magnetic memory, or another suitable memory. This non-transitory storage element may contain instruction commands and other data that enable controller 180 to perform the functions described herein. For example, controller 180 may be in communication with cathode bias power supply 115 such that IHC ion source 10 can vary the voltage applied to the filament 160 as a cathode. Controller 180 may also be in communication with reflector electrode power supply 123 to bias the reflector electrode. Further, controller 180 can monitor the voltage, current, and / or power supplied by cathode bias power supply 115.

[0022] FIG. 2 shows an ion implantation system using the IHC ion source 10 of FIG. 1. One or more electrodes 200 are disposed outside and in the vicinity of the extraction aperture of the IHC ion source 10.

[0023] Downstream from the electrode 200, a mass spectrometer 210 is arranged. The mass spectrometer 210 uses a magnetic field to direct the path of the extracted ribbon ion beam 1. The magnetic field affects the flight path of the ions according to their mass and charge. A mass resolving device 220 having a resolving aperture 221 is arranged at the output (i.e., the distal end) of the mass spectrometer 210. By appropriately selecting the magnetic field, only those ions in the ribbon ion beam 1 having the selected mass and charge will be directed through the resolving aperture 221. Other ions will collide with the wall of the mass resolving device 220 or the mass spectrometer 210 and will not be able to move further within the system.

[0024] A collimator 230 may be arranged downstream from the mass resolving device 220. The collimator 230 receives ions from the ribbon ion beam 1 that has passed through the resolving aperture 221 and generates a ribbon ion beam formed from a plurality of parallel or substantially parallel beamlets. The output (i.e., the distal end) of the mass spectrometer 210 and the input (i.e., the proximal end) of the collimator 230 may be spaced apart by a certain distance. The mass resolving device 220 is arranged in the space between these two components.

[0025] Downstream from the collimator 230, an acceleration / deceleration stage 240 may be arranged. The acceleration / deceleration stage 240 may be referred to as an energy purity module. The energy purity module is a beam line lens component configured to independently control the deflection, deceleration, and focusing of the ion beam. For example, the energy purity module may be a vertical electrostatic energy filter (VEEF) or an electrostatic filter (EF). Downstream from the acceleration / deceleration stage 240, a platen 260 is arranged. A workpiece is arranged on the platen 260 during processing.

[0026] Referring back to FIG. 1, in this embodiment, the extraction plate 103 has a varying thickness. The extraction plate 103 protrudes inwardly from the inner surface facing the chamber 100. In other words, the protrusion 150 extends from the inner surface of the extraction plate 103 into the chamber, changing the thickness of the extraction plate 103. This protrusion 150 affects the thickness of the extraction opening 140. In turn, the thickness of the extraction opening 140 affects the loss area disposed within the extraction opening 140. The thickness of the extraction opening 140 is defined as the distance between the inner surface and the outer surface of the extraction plate 103 for a particular position in the width direction. The thickness of the extraction opening 140 may vary across the X (i.e., width) direction.

[0027] The protrusion 150 is conductive and is in electrical communication with the wall of the chamber 100. Thus, when ions are extracted from the chamber 100 through the extraction opening 140, the protrusion 150 may increase the area of the extraction plate 103, which functions as a sink for free electrons and ions. The region of the thicker (i.e., larger in the Z direction) extraction opening 140 may have a larger loss area and thus may neutralize more ions than the region of the thinner extraction opening 140. In this way, the plasma density within the extraction opening 140 proximate to the protrusion 150 can be reduced compared to regions having thinner protrusions or no protrusions. As an example, in certain embodiments, the plasma density may be greatest near the center of the chamber 100. By introducing the protrusion 150 within this area, the extraction opening 140 near the center of the chamber 100 may be thicker than other portions of the extraction opening 140, and the plasma density can be reduced in this area.

[0028] Thus, in certain embodiments, the protrusion 150 extends inwardly from the inner surface of the extraction plate 103 into the chamber 100. However, the outer surface of the extraction plate 103 facing away from the chamber 100 may remain unchanged and flat. More specifically, in this embodiment, the protrusion 150 extends in the Z direction. Further, the thickness of the protrusion 150 (measured in the Z direction) may vary as a function of its position in the width direction (i.e., the X direction). For example, the thickness of the extraction plate 103 may be greatest at the center of the extraction opening 140 and decrease as it moves away from the center towards the first end 104 and the second end 105. As used herein, the term "center of the extraction opening" refers to the center of the extraction opening in the X (i.e., width) direction.

[0029] In certain embodiments, the maximum difference between the thinnest portion of the extraction plate 103 and the thickest portion of the extraction plate may be between 1 mm and 5 mm. In other words, the protrusion may extend into the chamber 100 by at least 1 mm. Of course, in other embodiments, other dimensions may be used. In other words, the thickness of the extraction opening 140 through which ions pass may vary.

[0030] In certain embodiments, the protrusion 150 may have a smooth radius of curvature along the X direction, similar to that shown in FIG. 1. However, other curvatures are possible. For example, there may be a first radius of curvature between the first end 104 and the center of the extraction opening 140, and a second radius of curvature between the second end 105 and the center of the extraction opening 140. Further, although FIG. 1 shows the protrusion 150 extending to the first end 104 and the second end 105, in other embodiments, the protrusion 150 may be smaller in the width direction. Thereby, as shown in FIG. 3A, the protrusion 150 starts at a position between the first end 104 and the first edge 141 of the extraction opening 140 and terminates between the second edge 142 of the extraction opening 140 and the second end 105.

[0031] Furthermore, the protrusion 150 may have other shapes. For example, as shown in FIG. 3B, the protrusion 150 may appear as a triangular shape. The thickness of the extraction plate 103 increases linearly from the first end 104 to the center of the extraction opening 140 and from the second end 105 to the center of the extraction opening 140. In another embodiment, the protrusion 150 starts at a position between the first end 104 and the first edge 141 of the extraction opening 140 and terminates at a position between the second edge 142 of the extraction opening 140 and the second end 105.

[0032] Alternatively, as shown in FIG. 3C, the protrusion 150 may be trapezoidal. The thickness of the extraction plate 103 increases linearly from the first end 104 and from the second end 105 to a flat region positioned near the center of the extraction opening 140. In another embodiment, the protrusion 150 starts at a position between the first end 104 and the first edge 141 of the extraction opening 140 and terminates at a position between the second edge 142 of the extraction opening 140 and the second end 105.

[0033] FIG. 4A is a perspective view of the inner surface of the extraction plate 103 according to an embodiment. FIG. 4B shows a cross-sectional view of this extraction plate 103 taken along line A-A'. In this embodiment, the protrusion 150 starts at the first end 104 and extends to the second end 105. Furthermore, the protrusion 150 has a constant radius of curvature throughout the width direction.

[0034] In this embodiment, as best seen in FIG. 4B, the protrusion 150 tapers from the outer surface to the inner surface along the extraction opening 140 in the Y (i.e., height) direction. In other words, the extraction opening 140 is higher in the height direction at the inner surface 145 than at the outer surface 146 of the extraction opening 140. In some embodiments, the taper slope is constant along the width of the extraction opening 140. In a plurality of other embodiments, the taper slope may vary as a function of the width. For example, in FIG. 4A, the slope near the center of the extraction opening 140 may not be as steep as the slopes near the first end 141 and the second end 142. In fact, near the edge, the taper may be perpendicular or substantially perpendicular to the outer surface of the extraction plate 103.

[0035] FIG. 4C is a perspective view of the inner surface of the extraction plate 103 according to an embodiment. FIG. 4D shows a cross-sectional view of this extraction plate 103 taken along line B-B'. In this embodiment, the height of the extraction opening 140 in the Y direction remains constant along the Z direction. In other words, as best seen in FIG. 4D, the upper edge and the lower edge of the extraction opening 140 are perpendicular to the flat outer surface. Accordingly, the height of the extraction opening 140 at the inner surface 145 is equal to the height of the extraction opening 140 at the outer surface 146.

[0036] FIGS. 4A-4D show the protrusions 150 present on both sides of the extraction opening 140 in the height direction, but a plurality of other embodiments are possible. For example, in certain embodiments, as shown in FIG. 5A, the protrusion 150 is disposed on only one side of the extraction opening in the height direction. FIGS. 5A-5B represent cross-sectional views of the chamber 100. In other words, the extraction opening 140 divides the extraction plate 103 in the height direction. Accordingly, in some embodiments, the protrusion 150 is disposed on the portion of the extraction plate 103 above the extraction opening 140 in the height direction. In a plurality of other embodiments, the protrusion 150 is disposed on the portion of the extraction plate 103 below the extraction opening 140 in the height direction.

[0037] In other embodiments, as shown in FIG. 5B, etc., the thickness of the protrusion 150 on the portion of the extraction plate 103 above the extraction opening 140 may be different from the thickness of the protrusion 150 on the portion of the extraction plate 103 below the extraction opening 140. In certain embodiments, the thicker protrusion may be above the extraction opening 140, while in other embodiments, the thicker protrusion may be below the extraction opening 140.

[0038] Furthermore, FIGS. 4A-4D and FIGS. 5A-5B show that the thickness of the extraction plate 103 is constant for all values of height, except for the area around the extraction opening 140 at a specific width position. In other words, at a specific position in the X direction, the thickness of the extraction plate 103 is constant for all values of Y, except in the vicinity of the extraction opening 140. However, other embodiments are possible. For example, as shown in FIG. 6A, there may be a constant radius of curvature along the height direction. Alternatively, there may be a taper such that the thickness of the extraction plate 103 at the midpoint of the extraction opening 140 in the height direction is greater than at other positions in the height direction. Further, in certain embodiments, as shown in FIG. 6B, the protrusion 150 may be formed as a fin. In this embodiment, the protrusion 150 may be rectangular and may be disposed close to the extraction opening 140.

[0039] Furthermore, FIGS. 1 and 3A-3C show the maximum thickness of the protrusion 150 occurring at the center of the extraction opening 140, but other embodiments are possible. For example, as shown in FIG. 3D, the maximum thickness of the protrusion 150 may occur close to the first end 104 and / or the second end 105. This may be beneficial when the ion source generates a higher plasma density near the ends.

[0040] Furthermore, all of those drawings show protrusions 150 that are symmetric around the center of the extraction opening 140. However, a plurality of other embodiments are possible. For example, the plasma density within the ion source may be distributed as follows. That is, the density near the first end 104 may be greater than the density near the second end 105. In this case, as shown in FIG. 3E, the maximum (or minimum) thickness of the protrusion may occur nearer the first end 104 than nearer the second end 105.

[0041] Furthermore, the protrusions 150 may not be symmetric. Rather, the thickness of the protrusions 150 may vary in the X direction in any desired pattern.

[0042] All of the plurality of embodiments and drawings thus far have shown and described the protrusions 150 on the inner surface 145 of the extraction plate 103. However, a plurality of other embodiments are possible. For example, as described above, it is the thickness of the extraction plate 103 in the Z direction that determines the loss area. Thus, any mechanism that increases the thickness of the extraction opening 140 will affect the loss area and the ion density extracted.

[0043] Thus, in certain embodiments such as shown in FIG. 7, the protrusions may be disposed on the outer surface 146 of the extraction plate 103. In certain embodiments, the maximum difference between the thinnest part and the thickest part of the extraction plate 103 may be between 1 mm and 5 mm. In other words, the protrusions may extend outwardly from the outer surface by at least 1 mm. Of course, in other embodiments, other dimensions may be used. In these embodiments, the thickness of the extraction opening 140 through which ions pass may vary.

[0044] Furthermore, although FIG. 7 shows an outer surface protrusion 159 having a constant radius of curvature from the first end 104 to the second end 105, any of the shapes described herein may be used with the outer surface protrusion 159. For example, as shown in FIGS. 3B - 3C, the outer surface protrusion 159 may be triangular or trapezoidal. Further, the outer surface protrusion 159 need not extend from the first end 104 to the second end 105, as shown in FIG. 3A. Further, as shown in FIG. 3E, the outer surface protrusion 159 may be asymmetric in the width direction. As shown in FIG. 3D, the outer surface protrusion 159 may be thicker at the ends. Further, the extraction opening 140 may taper in the height direction, as shown in FIG. 4B, or need not taper, as shown in FIG. 4D. Further, as shown in FIGS. 5A - 5B, the outer surface protrusion 159 may be asymmetric in the height direction. The outer surface protrusion 159 may have a constant radius of curvature in the height direction, as shown in FIG. 6A, or may be formed as fins, as shown in FIG. 6B.

[0045] The above-described is an ion source that is an IHC ion source. However, other ion sources may also be used with this extraction plate 103. For example, a magnetized DC plasma source, a tubular cathode source, a Bernas ion source, and an inductively coupled plasma (ICP) ion source may also use this extraction plate 103 having the protrusion 150. For example, when an inductively coupled plasma (ICP) ion source is used, one of the walls 101 may be made of a dielectric material. Thereby, RF energy from an external antenna can enter into the chamber 100. Thus, the extraction plate may be used with ion sources having various different plasma generators.

[0046] Furthermore, although the wall 101 has been described as being conductive, it is understood that a non-conductive liner may be disposed in contact with the inner surface of the wall 101.

[0047] The present system and method have many advantages. Without being bound by a particular theory, it is believed that some of the ions extracted from chamber 100 are neutralized through contact with extraction plate 103. In other words, the surface of extraction aperture 140 functions as a loss area for ions when the ions are extracted. The number or proportion of ions that are neutralized can be a function of the distance the ions travel through extraction aperture 140. Thus, by making extraction plate 103 thicker in some regions, the loss area is increased and, accordingly, the number of ions that are neutralized is increased.

[0048] For example, the ion density of an extracted ion beam proximate to a thin portion of the extraction aperture can be reduced at a first rate, such as 50%. However, the ion density of an extracted ion beam proximate to a thick portion of the extraction aperture can be reduced at a second rate that is greater than the first rate, such as 75%. By introducing a protrusion into extraction plate 103, the distance the ions travel while being extracted through the extraction aperture can be altered. The protrusion functions as a sink for free electrons and ions. Thereby, the ion density within the extraction aperture proximate to protrusion 150 is reduced.

[0049] In other words, it is believed that the plasma density can be greater near the center of extraction aperture 140, but by increasing the thickness of extraction aperture 140 within this region, the total number of ions extracted from this region can be reduced. Further, if the extraction current is known as a function of width, it may be possible to appropriately shape protrusion 150 to increase the loss area along extraction aperture 140 over the width. Thereby, the extracted ion beam current is made substantially constant along the width direction.

[0050] In a certain test, the beam current was measured at a first point 1 inch to the left of the center along the X direction and a second point 1 inch to the right of the center along the X direction at the center of the extraction aperture 140. Arsenic gas was introduced into the IHC ion source 10 and ionized. The extraction power supply 170 was biased to 35 kV. With the unchanged extraction aperture, the beam current at the first point was about 90% of the beam current at the center, while the beam current at the second point was about 80% of the beam current at the center.

[0051] Next, an extraction plate having a protrusion 150 with a constant radius of curvature and extending about 4 mm into the chamber 100 was installed. The above experiment was repeated, and the beam current at the first point was substantially the same as the beam current at the center, while the beam current at the second point was about 90% of the beam current at the center. This corresponds to an improvement in uniformity of about 50%.

[0052] In a second test, phosphorus gas was introduced into the IHC ion source and ionized. The extraction power supply 170 was biased to 35 kV. With the unchanged extraction aperture, the beam current at the first point was about 93 percent of the beam current at the center, while the beam current at the second point was about 67 percent of the beam current at the center.

[0053] Next, the above-described extraction plate was installed and the above experiment was repeated. The beam current at the first point was substantially the same as the beam current at the center, while the beam current at the second point was about 75% of the beam current at the center. This corresponds to an improvement in uniformity of about 30%.

[0054] Further tests were conducted, showing that the uniformity of the ribbon ion beam was improved by 20% to 50% compared to the conventional extraction plate.

[0055] The present disclosure is not limited to the scope by the specific plurality of embodiments described herein. In fact, in addition to what is described herein, various other embodiments and modifications of the present disclosure will be apparent to those skilled in the art from the foregoing description and the accompanying drawings. Accordingly, such other embodiments and modifications are intended to be included within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of specific embodiments for specific purposes in a specific environment, those skilled in the art will recognize that its utility is not limited thereto, and that the present disclosure can be beneficially implemented in any number of environments for any number of purposes. Therefore, the claims described below are to be construed in view of the broadest possible scope and spirit of the present disclosure described herein.

Claims

1. A chamber comprising a first end, a second end, and a plurality of walls connecting the first end and the second end, wherein one of the plurality of walls is an extraction plate having an extraction opening with a width greater than the height, and a plasma generator for generating plasma within the chamber, The extraction plate includes a protrusion extending at least 1 mm into the chamber from the inner surface of the extraction plate at at least one location such that the thickness of the extraction opening varies as a function of the width of the extraction opening. An ion source.

2. The ion source according to claim 1, wherein the protrusion has a constant radius of curvature from the first end to the second end.

3. The ion source according to claim 1, wherein the protrusion has a triangular shape.

4. The ion source according to claim 1, wherein the protrusion has a trapezoidal shape.

5. The ion source according to claim 1, wherein the maximum thickness of the protrusion occurs at the center of the extraction opening in the width direction.

6. The extraction opening penetrates the protrusion, and the edge of the extraction opening tapers in the height direction, whereby the height of the extraction opening inside the chamber is greater than the height of the extraction opening on the outer surface of the extraction plate. The ion source according to claim 1.

7. The extraction opening penetrates the protrusion, and the edge of the extraction opening is such that the height of the extraction opening inside the chamber is equal to the height of the extraction opening on the outer surface of the extraction plate. The ion source according to claim 1.

8. A chamber comprising a first end, a second end, and a plurality of walls connecting the first end and the second end, wherein one of the plurality of walls is an extraction plate having an extraction opening with a width greater than the height, and a plasma generator for generating plasma within the chamber, the thickness of the extraction opening varies as a function of the width of the extraction opening, The extraction plate includes a protrusion for changing the thickness of the extraction opening, and the protrusion above the extraction opening in the height direction has a different thickness from the protrusion below the extraction opening in the height direction. An ion source. **Claim 9**: A chamber comprising a first end, a second end, and a plurality of walls connecting the first end and the second end, wherein one of the plurality of walls is an extraction plate having an extraction opening with a width greater than its height, and comprising a plasma generator for generating plasma within the chamber, wherein the thickness of the extraction opening varies as a function of the width of the extraction opening, wherein the extraction plate comprises a protrusion for varying the thickness of the extraction opening, and the protrusion is disposed only on one side of the extraction opening in the height direction, an ion source. **Claim 10** The ion source according to claim 1, wherein the plasma generator comprises an indirectly heated cathode disposed at the first end. **Claim 11** An extraction plate for use with an ion source, having an inner surface, an outer surface adapted to fit within a chamber, and an extraction opening having a width greater than its height, wherein the extraction plate comprises a protrusion extending at least 1 mm into the chamber from the inner surface of the extraction plate at at least one location such that the thickness of the extraction opening varies as a function of the width of the extraction opening. **Claim 12** The extraction plate according to claim 11, wherein the maximum thickness of the protrusion occurs at the center of the extraction opening in the width direction. **Claim 13** The extraction plate according to claim 11, wherein the extraction opening penetrates the protrusion and the edges of the extraction opening taper in the height direction, such that the height of the extraction opening inside the chamber is greater than the height of the extraction opening at the outer surface of the extraction plate. **Claim 14** The extraction plate according to claim 11, wherein the extraction opening penetrates the protrusion and the edges of the extraction opening are such that the height of the extraction opening inside the chamber is equal to the height of the extraction opening at the outer surface of the extraction plate. **Claim 15**: An extraction plate for use with an ion source, having an inner surface, an outer surface adapted to fit within a chamber, and an extraction opening having a width greater than its height, wherein the thickness of the extraction opening varies as a function of the width of the extraction opening, wherein the extraction plate comprises a protrusion on the inner surface or the outer surface, and the protrusion above the extraction opening in the height direction has a different thickness from the protrusion below the extraction opening in the height direction.

16. An extraction plate used together with an ion source, having an inner surface adapted within a chamber, an outer surface, and an extraction opening having a width greater than its height, wherein the thickness of the extraction opening varies as a function of the width of the extraction opening, the extraction plate comprising a protrusion on the inner surface or the outer surface, the protrusion being disposed only on one side of the extraction opening in the height direction.

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