Mismatch optical system for angle control of an extraction ion beam

Abstract

An ion source is disclosed that can extract a ribbon ion beam with improved uniformity of vertical angular spread. The extraction plate and extraction optics are designed such that there is at least one non-uniform gap between adjacent components. The non-uniform gap can be effective in reducing the non-uniformity of the angular spread of the extracted ribbon ion beam. Specifically, for a given gap in the Z direction, ions extracted from a region with low plasma density may have a large vertical angular spread. A large gap in the Z direction between components in this region may result in the vertical angular spread being closer to the vertical angular spread of ions extracted from a region with high plasma density. The non-uniform gap may be created by having a flat or curved extraction plate and an electrode that is flat, convex, or concave. In certain embodiments, the non-uniform gap is disposed between the extraction plate and the suppression electrode.

Description

Technical Field

[0001] This application claims the benefit of U.S. Patent Application No. 17 / 510,996, filed Oct. 26, 2021, the disclosure of which is hereby incorporated by reference in its entirety.

[0002] This disclosure describes a system for controlling the angular spread of a ribbon ion beam extracted from an ion source, such as 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 positive voltage 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, an IHC 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 angular spread of the extracted ribbon ion beam is not uniform along its width. For example, the range of beam angles near the center of the ribbon ion beam may be smaller than the range of beam angles near the edges of the ribbon ion beam. In some 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, a system that can control the uniformity of the vertical angular spread of the ribbon ion beam being extracted from the ion source would be beneficial. SUMMARY OF THE INVENTION

[0006] An ion source is disclosed that can extract a ribbon ion beam with improved uniformity of vertical angular spread. The extraction plate and extraction optics are designed such that there is at least one non-uniform gap between adjacent components. The non-uniform gap can be effective in reducing the non-uniformity of the angular spread of the extracted ribbon ion beam. Specifically, when a given gap is provided in the Z direction, ions extracted from regions with a low plasma density may have a larger vertical angular spread. If the gap in the Z direction between components in this region is large, the vertical angular spread may approach that of ions extracted from regions with a high plasma density. The non-uniform gap may be created by having a flat or curved extraction plate and an electrode that is flat, convex, or concave. In certain embodiments, the non-uniform gap is disposed between the extraction plate and the suppression electrode.

[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, wherein one of the plurality of walls is an extraction plate having an extraction opening with a width greater than its height, a plasma generator for generating plasma within the chamber, and a suppression electrode disposed outside the chamber and close to the extraction opening. The gap between the outer surface of the extraction plate and the surface of the suppression electrode facing the extraction plate is non-uniform in the width direction. The difference in the gap is at least 0.3 mm. In some embodiments, plasma is generated within the chamber and the plasma density within the chamber is non-uniform. A first region within the chamber has a higher plasma density than a second region. The gap between the outer surface of the extraction plate and the surface of the suppression electrode facing the extraction plate is smaller near the first region than near the second region. In some embodiments, the plasma density is higher at the center of the extraction opening than at the edge of the extraction opening. In certain embodiments, the outer surface of the extraction plate is flat and the surface of the suppression electrode facing the extraction plate is convex. In certain embodiments, the outer surface of the extraction plate is convex and the surface of the suppression electrode facing the extraction plate is flat. In certain embodiments, the outer surface of the extraction plate is convex and the surface of the suppression electrode facing the extraction plate is convex. In some embodiments, the plasma density is higher at the edge of the extraction opening than at the center of the extraction opening. In certain embodiments, the outer surface of the extraction plate is flat and the surface of the suppression electrode facing the extraction plate is concave. In certain embodiments, the outer surface of the extraction plate is concave and the surface of the suppression electrode facing the extraction plate is flat or concave. In some embodiments, the plasma generator includes an indirectly heated cathode. In some embodiments, plasma is generated within the chamber and the plasma density within the chamber is non-uniform. The gap between the outer surface of the extraction plate and the surface of the suppression electrode facing the extraction plate is smallest where the plasma density is highest.In certain embodiments, the ion source comprises at least one additional electrode arranged such that a suppression electrode is disposed between the at least one additional electrode and an extraction plate. A second non-uniform gap is disposed between a set of adjacent electrodes.

[0008] According to another embodiment, an ion implantation system is disclosed. The ion implantation system comprises the ion source, a mass analyzer, and a platen as described above.

[0009] According to another embodiment, an ion source is disclosed. The ion source is 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, a plasma generator for generating plasma within the chamber, a suppression electrode disposed outside the chamber and proximate to the extraction opening, and at least one additional electrode arranged such that the suppression electrode is disposed between the at least one additional electrode and the extraction plate. A non-uniform gap in the width direction is disposed between a set of adjacent electrodes. In some embodiments, the at least one additional electrode includes a ground electrode and the non-uniform gap is disposed between the suppression electrode and the ground electrode. In certain embodiments, the surface of the suppression electrode facing the ground electrode is convex and the surface of the ground electrode facing the suppression electrode is flat or convex. In certain embodiments, the surface of the suppression electrode facing the ground electrode is flat and the surface of the ground electrode facing the suppression electrode is convex. In some embodiments, the at least one additional electrode includes a second electrode and a third electrode and the non-uniform gap is disposed between the suppression electrode and the second electrode or between the second electrode and the third electrode. In some embodiments, the at least one additional electrode includes a second electrode, a third electrode, and a fourth electrode and the non-uniform gap is disposed between the suppression electrode and the second electrode, between the second electrode and the third electrode, or between the third electrode and the fourth electrode.

[0010] According to another 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, wherein one of the plurality of walls is an extraction plate having an extraction opening, the direction between the first end and the second end is the X direction, the direction perpendicular to the X direction is the Y direction, the extraction opening has a dimension in the X direction larger than the dimension in the Y direction, a plasma generator for generating plasma in the chamber, and a suppression electrode disposed outside the chamber and close to the extraction opening. The gap between the outer surface of the extraction plate and the surface of the suppression electrode facing the extraction plate is non-uniform in the X direction. The difference in the gap is at least 0.3 mm.

[0011] 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

[0012]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0013] FIG. 1 shows an IHC ion source 10 having an extraction optical system 150 that can be used to extract a ribbon ion beam with improved vertical angle uniformity according to one embodiment. In this embodiment, 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, i.e., an extraction plate 103 and a bottom wall opposing the extraction plate 103. The extraction plate 103 includes an extraction opening 140 through which ions are extracted. The extraction opening 140 may be considerably larger in the width direction (also referred to as the X direction) than in the height direction (also referred to as the Y direction). The X direction may be defined as the direction between a first end 104 and a second end 105. The Y direction is perpendicular to the X 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 2 inches in the width direction and smaller than 0.5 inches in the height direction. Further, the extraction opening may be of any shape. In some embodiments, the extraction opening 140 may be oval or rectangular. In a plurality of other embodiments, the extraction opening 140 may have an irregular shape. In all embodiments, the longer dimension is referred to as the width and the shorter dimension is referred to as the height.

[0014] The wall 101 of the chamber 100 may be constructed of a conductive material (such as tungsten or another high melting point metal) 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. Thus, 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 -200V and -1500V relative to the voltage of the cathode 110. Then, the cathode 110 emits thermoelectrons into the chamber 100 from its front surface.

[0015] Thus, 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 filament 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 and ionizes 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.

[0016] 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.

[0017] 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 to repel electrons. For example, in certain embodiments, the reflective electrode 120 is biased between 0 and -150V 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 in a floating state, the reflective electrode 120 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.

[0018] 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 electromagnetic forces.

[0019] 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.

[0020] 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 beamline. 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.

[0021] 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 from 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.

[0022] The extraction optical system 150 is used to attract ions from within the chamber using an electric field. In certain embodiments, the extraction optical system 150 includes a suppression electrode 151. The suppression electrode 151 is negatively biased with respect to the plasma to attract ions through the extraction aperture 140.

[0023] The suppression electrode 151 can be a single conductive component in which a suppression aperture 153 is disposed. Alternatively, the suppression electrode 151 can be composed of two conductive components spaced apart to create a suppression aperture 153 therebetween. The suppression electrode 151 can be a metal such as titanium. The suppression electrode 151 can be electrically biased using a suppression power supply 155. The suppression electrode 151 can be biased to be more negative than the extraction plate 103. In certain embodiments, the suppression electrode 151 is negatively biased by the suppression power supply 155 to a voltage between -3 kV and -15 kV.

[0024] In other embodiments, the extraction optical system 150 includes a suppression electrode 151 and a ground electrode 152. The suppression electrode 151 is disposed between the extraction plate 103 and the ground electrode 152.

[0025] In these embodiments, the ground electrode 152 may be disposed close to the suppression electrode 151. Similar to the suppression electrode 151, the ground electrode 152 may be a single conductive component in which a ground opening 154 is disposed, or may be composed of two components spaced apart to create a ground opening 154 therebetween. The ground electrode 152 may be electrically grounded. Of course, in other embodiments, the ground electrode 152 may be biased using a separate power source. The extraction opening 140, the suppression opening 153, and the ground opening 154 are all aligned.

[0026] In other embodiments, the extraction optical system 150 may include more than two electrodes, for example, three electrodes or four electrodes. In these embodiments, the electrodes may be functionally and structurally similar to those described above, but may be biased at different voltages.

[0027] Each electrode has two surfaces. The first surface faces the IHC ion source 10 and may be referred to as the proximal surface or the ion source side surface. The second surface faces the platen 260 and may be referred to as the distal surface or the beam line side surface.

[0028] 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 MFC of each gas container 108 to regulate the flow rate 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 to enable the IHC ion source 10 to 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.

[0029] FIG. 2 shows an ion implantation system using the IHC ion source 10 of FIG. 1. An extraction optical system 150 is disposed outside and proximate to the extraction aperture of the IHC ion source 10. The extraction optical system 150 may include one or more electrodes.

[0030] Downstream of the extraction optical system 150, 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 part (i.e., the distal end) of the mass spectrometer 210. By appropriately selecting the magnetic field, only those ions in the extracted ribbon ion beam 1 having the selected mass and charge will be guided 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.

[0031] A collimator 230 can be arranged downstream from the mass resolving device 220. The collimator 230 receives ions from the extracted 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 part (i.e., the distal end) of the mass spectrometer 210 and the input part (i.e., the proximal end) of the collimator 230 can be separated by a certain distance. The mass resolving device 220 is arranged in the space between these two components.

[0032] 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.

[0033] In FIG. 1, the outer surface of the extraction plate 103 is convex. Thereby, the outer surface protrudes further from the chamber 100 at the center 107 than at the edge. The radius of curvature may be, for example, between 500 mm and 1000 mm. The center 107 of the extraction opening 140 is defined as the midpoint along the X-axis. Further, the suppression electrode 151 may be linear. In this way, in the Z direction, the gap between the outer surface of the extraction plate 103 and the ion source side surface of the suppression electrode 151 is not constant. Specifically, the central gap 141 disposed at the center 107 is smaller than the edge gap 142 at the edge of the extraction opening 140. In certain embodiments, the difference between the central gap 141 and the edge gap 142 may be at least 0.3 mm. In certain embodiments, the central gap 141 may be between 4 mm and 50 mm, while the edge gap 142 may be between 4.3 mm and 55 mm. Thus, a non-uniform gap is generated, the gap being in the Z direction and the non-uniformity being in the X direction, i.e., the width direction.

[0034] In certain embodiments, it has been found that when a given gap is provided in the Z direction, ions extracted from a region in the chamber having a low plasma density tend to have a larger angular spread in the vertical direction than ions extracted from a region having a high plasma density. By increasing the distance between the outer surface of the extraction plate 103 and the ion source side surface of the suppression electrode 151, this angular spread in the vertical direction can be made similar to the angular spread in the vertical direction associated with the high plasma density region. Thus, for an ion source where the plasma density is highest near the center 107, the configuration shown in FIG. 1 can reduce the angular spread in the vertical direction of the extracted ribbon ion beam, and thus make the angular spread in the vertical direction more uniform across the width direction.

[0035] Figure 3 shows the second embodiment. Using the second embodiment, when the plasma has the highest density at the center 107 of the chamber 100, the angular spread in the vertical direction can be reduced. In this embodiment, the outer surface of the extraction plate 103 is flat or planar, while the surface of the suppression electrode 151 facing the extraction plate 103 is convex. The radius of curvature of the suppression electrode 151 may be greater than 100 mm, for example, from 100 mm to 1000 mm. Similar to FIG. 1, this configuration enables the central gap 141 to be smaller than the edge gap 142. In some embodiments, the edge gap 142 may be at least 0.3 mm larger than the central gap 141.

[0036] In certain embodiments, both the outer surface of the extraction plate 103 and the proximal surface of the suppression electrode 151 may be convex.

[0037] In other embodiments, the plasma density can be lower at the center 107 than at the edges. In these embodiments, it may be desirable to have a central gap 141 that is larger than the edge gap 142. FIG. 4A shows a configuration that achieves this result. In this embodiment, the proximal surface of the suppression electrode 151 facing the extraction plate 103 is concave. The radius of curvature may be between 400 mm and 1000 mm. The outer surface of the extraction plate 103 is flat or planar. This enables the central gap 141 to be larger than the edge gap 142. Again, in some embodiments, the difference between the central gap 141 and the edge gap 142 may exceed 0.3 mm.

[0038] In another embodiment shown in FIG. 4B, the outer surface of the extraction plate 103 may be concave, while the proximal surface of the suppression electrode 151 may be flat or planar. This also enables the central gap 141 to be larger than the edge gap 142.

[0039] The foregoing disclosure discloses a non-uniform gap between the outer surface of the extraction plate 103 and the suppression electrode 151, but other embodiments are possible.

[0040] In a plurality of configurations in which the extraction optical system 150 includes two or more electrodes, gaps also exist between adjacent electrodes. For example, in FIG. 1, two electrodes are present, and thus a gap exists between the suppression electrode 151 and the ground electrode 152. In an extraction optical system having N electrodes, N is 2 or more, and N - 1 gaps exist between adjacent electrodes.

[0041] Thus, in certain embodiments, the non-uniform gaps described above may not exist between the outer surface of the extraction plate 103 and the proximal surface of the suppression electrode 151, but rather may exist between two adjacent electrodes in the extraction optical system 150.

[0042] FIG. 5 shows such an embodiment. In this embodiment, the outer surface of the extraction plate 103 is flat, and both sides of the suppression electrode 151 are the same. The proximal surface of the ground electrode 152 facing the suppression electrode 151 is convex. Thus, the gap between the suppression electrode 151 and the ground electrode 152 is non-uniform. In this embodiment, the central gap 141 is smaller than the edge gap 142. In certain embodiments, this difference may be at least 0.3 mm.

[0043] It should be noted that there are also a plurality of other configurations that result in the central gap 141 between the electrodes being smaller than the edge gap 142. For example, the distal surface of the suppression electrode 151 may be convex, while the proximal surface of the ground electrode 152 is flat. Alternatively, both the distal surface of the suppression electrode 151 and the proximal surface of the ground electrode 152 may be convex.

[0044] FIG. 6 shows an embodiment that realizes a larger central gap 141 between two adjacent electrodes. For example, the distal surface of the suppression electrode 151 is flat, while the proximal surface of the ground electrode 152 is concave. In this embodiment, the central gap 141 is larger than the edge gap 142. In certain embodiments, this difference may be at least 1 cm.

[0045] It should be noted that there are also a plurality of other configurations that result in the central gap 141 between the electrodes being larger than the edge gap 142. For example, the distal surface of the suppression electrode 151 may be concave, while the proximal surface of the ground electrode 152 is flat. Alternatively, both the distal surface of the suppression electrode 151 and the proximal surface of the ground electrode 152 may be concave.

[0046] Furthermore, FIGS. 5-6 show a non-uniform gap between the suppression electrode 151 and the ground electrode 152, but other configurations are also possible. For example, in an ion source where the extraction optical system has three electrodes, a non-uniform gap may exist between the suppression electrode and the second electrode, or between the second electrode and the third electrode. Similarly, in an ion source where the extraction optical system has four electrodes, a non-uniform gap may exist between the suppression electrode and the second electrode, between the second electrode and the third electrode, or between the third electrode and the fourth electrode.

[0047] Furthermore, FIGS. 1 and 3-6 show that at least one surface of each electrode is flat, but other configurations are also possible. For example, referring to FIG. 7, the outer surface of the extraction plate 103 is convex, and the proximal surface of the suppression electrode 151 is concave. Thereby, the gap between the proximal surface of the suppression electrode 151 and the outer surface of the extraction plate 103 is uniform. In one embodiment, the distal surface of the suppression electrode 151 may be convex, and the proximal surface of the ground electrode 152 is flat. Thereby, the gap between the suppression electrode 151 and the ground electrode 152 is non-uniform. In this way, the non-uniform gap shown in FIG. 1 has moved between the suppression electrode 151 and the ground electrode 152.

[0048] Furthermore, in certain embodiments, there may be two or more non-uniform gaps. For example, the extraction plate 103 of FIG. 1 may be combined with the ground electrode of FIG. 5 to create two non-uniform gaps. A first non-uniform gap may be between the outer surface of the extraction plate 103 and the proximal surface of the suppression electrode 151, and a second non-uniform gap may be between the distal surface of the suppression electrode 151 and the proximal surface of the ground electrode 152. Of course, other configurations of the extraction plate 103, suppression electrode 151, and ground electrode 152 may be used to achieve multiple non-uniform gaps. Further, when three or more electrodes are used, multiple non-uniform gaps may be present between any pair of adjacent electrodes.

[0049] The above disclosure has described convex and concave components, and the figures show that those components are symmetric about the center 107. However, other embodiments are possible. For example, when the plasma density is non-uniform and asymmetric in the X direction, the gap can also be designed to be asymmetric in the X, i.e., the width direction. For example, the plasma density may be highest at a position between the cathode 110 and the center 107. In this embodiment, the gap can be designed such that the minimum gap is present at the position in the X direction where the plasma density is highest. Thus, in certain embodiments, the gap is designed to complement the profile of the plasma density.

[0050] 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 these extraction optics 150. Thus, the extraction plate may be used with ion sources having various different plasma generators.

[0051] The present system and method have many advantages. In one test, a ribbon ion beam was extracted from an IHC ion source. In that case, the gap between the outer surface of the extraction plate 103 and the proximal surface of the suppression electrode 151 was uniform. The vertical angular spread near the center of the aperture was measured to be approximately 2° and was concentrated between -2° and +2°. However, the vertical angular spread near the edge of the extraction aperture was much larger. Specifically, there was a concentration between -1° and +1°, but there were also vertical angles of ±6°. The test was then repeated using an extraction plate 103 and a suppression electrode 151 configured to provide a non-uniform gap in the width direction. In that case, the largest gap was along the edge of the extraction aperture 140. In this test, the vertical angular spread near the center of the extraction aperture did not change, but the vertical angular spread near the edge was significantly modified. Specifically, the vertical angular spread was substantially uniform across the width of the ribbon ion beam. This can result in improved uniformity in the workpiece.

[0052] The present disclosure is not limited in scope by the specific plurality of embodiments described herein. Indeed, in addition to what is described herein, various other embodiments and modifications of the present disclosure will be apparent to those of ordinary skill 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 a particular purpose in a particular environment, those of ordinary skill in the art will recognize that its usefulness 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 set forth below are to be construed in view of the broadest possible scope of the disclosure described herein and the spirit thereof.

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 its height. A plasma generator for generating plasma within the chamber, and An ion source comprising a suppression electrode disposed outside the chamber and adjacent to the extraction opening, wherein plasma is generated within the chamber, the plasma density within the chamber is non-uniform, a first region within the chamber has a higher plasma density than a second region, in the width direction of the extraction opening, a gap between an outer surface of the extraction plate and a surface of the suppression electrode facing the extraction plate is smaller near the first region than near the second region, and a difference between the gap near the first region and the gap near the second region is at least 0.3 mm.

2. The ion source according to claim 1, wherein the plasma density is higher at the center of the extraction opening than at an edge of the extraction opening.

3. The ion source according to claim 2, wherein the outer surface of the extraction plate is flat and the surface of the suppression electrode facing the extraction plate is convex.

4. The ion source according to claim 2, wherein the outer surface of the extraction plate is convex and the surface of the suppression electrode facing the extraction plate is flat.

5. The ion source according to claim 2, wherein the outer surface of the extraction plate is convex and the surface of the suppression electrode facing the extraction plate is convex.

6. The ion source according to claim 1, wherein the plasma density is higher at the edge of the extraction opening than at the center of the extraction opening.

7. The outer surface of the extraction plate is flat, and the surface of the suppression electrode facing the extraction plate is concave. The ion source according to claim 6.

8. The outer surface of the extraction plate is concave, and the surface of the suppression electrode facing the extraction plate is flat or concave. The ion source according to claim 6.

9. The plasma generator includes an indirectly heated cathode. The ion source according to claim 1.

10. Plasma is generated in the chamber, the plasma density in the chamber is non-uniform, and the gap between the outer surface of the extraction plate and the surface of the suppression electrode facing the extraction plate is smallest where the plasma density is highest. The ion source according to claim 1.

11. The suppression electrode is further provided with at least one additional electrode arranged between the at least one additional electrode and the extraction plate, a second non-uniform gap is arranged between two adjacent electrodes, and the electrodes include the suppression electrode and the at least one additional electrode. The ion source according to claim 1.

12. The ion source according to claim 1, a mass spectrometer, and a platen. An ion implantation system.

13. 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. A chamber, A plasma generator for generating plasma in the chamber, A suppression electrode having an opening with a width greater than the height and arranged outside the chamber and close to the extraction opening, and An ion source comprising at least one further electrode arranged such that the suppression electrode is arranged between the at least one further electrode and the extraction plate, An ion source in which a non-uniform gap is arranged between two adjacent electrodes in the width direction of the opening, the electrodes including the suppression electrode and the at least one further electrode.

14. The ion source according to claim 13, wherein the at least one further electrode includes a ground electrode, and the non-uniform gap is arranged between the suppression electrode and the ground electrode.

15. The ion source according to claim 14, wherein the surface of the suppression electrode facing the ground electrode is convex, and the surface of the ground electrode facing the suppression electrode is flat or convex.

16. The ion source according to claim 14, wherein the surface of the suppression electrode facing the ground electrode is flat, and the surface of the ground electrode facing the suppression electrode is convex.

17. The ion source according to claim 13, wherein the at least one further electrode includes a second electrode and a third electrode, and the non-uniform gap is arranged between the suppression electrode and the second electrode or between the second electrode and the third electrode.

18. The ion source according to claim 13, wherein the at least one further electrode includes a second electrode, a third electrode, and a fourth electrode, and the non-uniform gap is arranged between the suppression electrode and the second electrode, between the second electrode and the third electrode, or between the third electrode and the fourth electrode.

19. A chamber comprising 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 being an extraction plate having an extraction opening, the direction between the first end and the second end being the X direction, the direction perpendicular to the X direction being the Y direction, and the extraction opening having a dimension in the X direction that is larger than the dimension in the Y direction. A plasma generator for generating plasma in the chamber, and An ion source comprising a suppression electrode disposed outside the chamber and close to the extraction opening, wherein plasma is generated in the chamber, the plasma density in the chamber is non-uniform, a first region in the chamber has a higher plasma density than a second region, in the X direction of the extraction opening, a gap between an outer surface of the extraction plate and a surface of the suppression electrode facing the extraction plate is smaller near the first region than near the second region, and a difference between the gap near the first region and the gap near the second region is at least 0.3 mm.

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