High bandwidth variable dose ion implantation system and method

Abstract

An ion implantation system 100 includes an ion source 108 that generates ions and creates an ion beam 112 along a beamline 160. Optionally, a mass analyzer 126 is disposed downstream of the ion source and generates a magnetic field according to a selected mass-to-charge ratio. The beamline formed by the ion beam is directed to a workpiece target 122. A gating device includes one or more of a mechanical gating device 136 configured to block or deflect the ion beam from contacting the workpiece target or a power control gating device configured to cut off power to the ion source. A beam-to-workpiece target translation mechanism changes the beam-to-workpiece target position while the ion beam is gated by the gating device. Methods of implanting ions on a workpiece in a predetermined distribution by multiple scans are disclosed. These systems and methods allow implantation distributions to be achieved that have smooth curvatures and / or significant differences in dose characteristics at adjacent locations.

Description

[0001] Cross-references to related applications This application claims priority to U.S. Provisional Application No. 63 / 599,710, filed November 16, 2023, entitled “High-bandwidth Variable-Dose Ion Implantation System and Method”. That earlier application is incorporated herein by reference for all purposes. Technical Field

[0002] This disclosure relates generally to ion implantation systems, and more specifically to ion implantation systems with controlled dose capability. Background Technology

[0003] In semiconductor device manufacturing, ion implantation is used to dope semiconductors with impurities. Ion implantation systems are typically used to dope workpieces (such as semiconductor wafers) with ions from an ion beam to produce n-type or p-type material dopant or to form passivation layers during integrated circuit manufacturing. This beam treatment is typically used to selectively implant impurities containing specified dopant materials into wafers at predetermined energy levels and controlled concentrations to produce semiconductor materials during integrated circuit manufacturing. When used to dope semiconductor wafers, ion implantation systems implant selected ion species into the workpiece to produce the desired intrinsic material. For example, when implanting ions into silicon wafers, ions from source materials such as antimony, arsenic, or phosphorus produce “n-type” intrinsic material wafers, while ions from source materials such as boron, gallium, or indium typically produce “p-type” intrinsic material wafers. For example, when implanting ions into silicon carbide (SiC) wafers, nitrogen (n-type dopant) and aluminum (p-type dopant) are typically used as ion species.

[0004] A typical ion implanter includes an ion source, an ion extraction unit, a mass analysis unit, with or without a post-acceleration section, a beam delivery unit, and a wafer processing unit. The ion source generates ions of the desired atomic or molecular dopant species. These ions are extracted from the ion source by an ion extraction unit (typically a set of electrodes) that excites and directs the ion stream from the ion source, forming an ion beam. The desired ions are separated from the ion beam, typically by mass dispersion or separation of the extracted ion beam using magnetic dipoles. The beam delivery unit is typically a vacuum system containing a series of focusing and acceleration / deceleration devices that transports the analyzed ion beam to the wafer processing unit while maintaining the desired characteristics of the ion beam. Finally, the semiconductor wafer or other target for implantation is moved into and out of the wafer processing unit by a wafer handling system (which may include one or more robotic arms) to position the wafer to be processed in front of the analyzed ion beam and remove the processed wafer from the ion implanter.

[0005] In many ion implantation systems, the physical size of the ion beam is smaller than the target workpiece, so the ion beam scans in one or more directions to adequately cover the surface of the target workpiece. Typically, electrostatic or magnetic beam scanners scan the ion beam in the fast scanning direction, while mechanical devices move the target workpiece in the slow scanning direction to provide adequate coverage of the ion beam across the workpiece surface.

[0006] Traditionally, the goal of ion implantation is to provide uniform implantation across the entire wafer, but increasingly complex applications require a specific dose profile. This can be achieved by varying the beam velocity to the workpiece target. However, a drawback of this approach is that the variability of the dose is limited by the scanning speed range of the system used to scan the beam or workpiece. This scanning speed range is typically determined by the system bandwidth (i.e., the electrical, magnetic, or mechanical scanning speed of the wafer or beam). Summary of the Invention

[0007] This disclosure recognizes the significant need for ion implantation systems to produce variable or controlled doses to achieve highly precise and predetermined implantation. Therefore, systems and methods are provided herein for providing variable or controlled doses in a manner that allows for precise doping to a desired distribution.

[0008] Therefore, a brief overview of this disclosure is presented below to provide a basic understanding of some aspects of this disclosure. This overview is not a comprehensive summary of this disclosure. It is neither intended to identify key or essential elements of the invention nor to depict the scope of the invention. Its purpose is to present some concepts of this disclosure in a simplified form as a prelude to the more detailed description that follows.

[0009] In some aspects, the technology described herein relates to an ion implantation system comprising: an ion source that generates ions and produces an ion beam along a beamline; a workpiece target associated with the beamline; a controller configured to control a beam-to-workpiece target translation mechanism to move the ion beam relative to the workpiece target, thereby moving the beam-to-workpiece target position at a beam-to-workpiece target velocity; and a gating device comprising one or more of the following: a mechanical gating device configured to block or deflect the ion beam from being guided to the workpiece target; a power control gating device configured to cut off the power supply to the ion source; or a magnetic, electromagnetic, or electric beam deflection device configured to deflect the ion beam from being guided to the workpiece target; wherein the beam-to-workpiece target translation mechanism changes the beam-to-workpiece target position while the ion beam is gated by the gating device.

[0010] In some aspects, the technology described herein relates to a method for performing ion implantation, comprising: generating an ion beam; moving the ion beam relative to a workpiece target in a first scan, thereby moving the beam to a workpiece target position at a first beam-to-workpiece target velocity; and gating the ion beam during said first scan while continuing to move the beam to the workpiece target position.

[0011] The above overview is intended only to provide a brief summary of some features of some embodiments of this disclosure, and other embodiments may include additional and / or different features in addition to those described above. In particular, this overview should not be construed as limiting the scope of this application. Therefore, to achieve the foregoing and related objectives, this disclosure includes the features fully described below and specifically pointed out in the claims. The following description and drawings illustrate certain illustrative embodiments of the invention in detail. However, these embodiments indicate several of a variety of ways in which the principles of the invention can be employed. Other objects, advantages, and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. Furthermore, features of the various embodiments and examples described herein can be combined with each other unless otherwise specifically stated. Attached Figure Description

[0012] Figure 1A This is a simplified top view of an ion implantation system according to aspects of this disclosure.

[0013] Figure 1B This is a schematic block diagram illustrating an example of a beam control circuit for an ion implantation system, which is used to start or terminate the ion beam by switching the extraction voltage and / or suppression voltage applied to the respective electrodes associated with the ion source of the ion implantation system.

[0014] Figure 2 It is a graph showing the comparison between the desired dose distribution and the required beam-to-target velocity distribution.

[0015] Figure 3 It is a graph showing the desired total dose distribution superimposed on the first pattern 302 and the second pattern 304, where the relative dose is on the y-axis and the wafer position is on the x-axis.

[0016] Figure 4 It is a graph showing the first to tenth scan patterns 401-410, where the relative dose is on the y-axis and the wafer position is on the x-axis.

[0017] Figure 5 It is a graph showing the first to tenth scan patterns 501-510, where the relative dose is on the y-axis and the wafer position is on the x-axis.

[0018] Figure 6It is a graph showing the first to twentieth scan patterns 601-620, where the normalized dose is on the y-axis and the wafer position is on the x-axis.

[0019] Figure 7 It shows the curves of the first to twentieth scan patterns 701-720, where the ion beam width is 100 mm, the normalized dose is on the y-axis, and the wafer position is on the x-axis.

[0020] Figure 8 Is with Figure 7 A similar graph, but with the scan pattern removed, showing only the expected dose and the predicted actual dose when using a 100mm beam.

[0021] Figure 9 It is a graph showing the first to twentieth scan patterns 901-920, where the normalized dose is on the y-axis and the wafer position is on the x-axis.

[0022] Figure 10 This shows the execution of, such as Figure 9 The actual ion implantation dose on the wafer was measured after a set of patterns shown.

[0023] Figure 11 Is with Figure 10 A similar graph, but with the pattern removed, showing only the expected dose 1102 and the observed actual dose 1104 when using a 100mm beam.

[0024] Figure 12 This is a flowchart of an example method for performing ion implantation.

[0025] Figure 13 This is a flowchart of an example method for ion implantation, which focuses on beam calibration and calculating a set scanning pattern to achieve a desired dose distribution. Detailed Implementation

[0026] This disclosure generally relates to various apparatuses, systems, and methods associated with ion implantation into a workpiece. More specifically, this disclosure relates to an ion implantation system and method for providing a controlled or variable dose to match a predetermined distribution.

[0027] Therefore, the present technology is described with reference to the accompanying drawings, wherein the same reference numerals may be used to refer to the same elements. It should be understood that the description of these aspects is illustrative only and should not be construed in a limiting sense. In the following description, numerous specific details are set forth for purposes of explanation to provide a thorough understanding of the technology described herein. Furthermore, the scope of the invention is not intended to be limited to the embodiments or examples described below with reference to the accompanying drawings, but only to the appended claims and their equivalents.

[0028] It should also be noted that the accompanying drawings are provided to illustrate some aspects of embodiments of this disclosure and should therefore be considered exemplary. In particular, the elements shown in the drawings are not necessarily to scale, and the placement of the various elements in the drawings is chosen to provide a clear understanding of the respective embodiments and should not be construed as necessarily representing the actual relative positions of the various components in all embodiments covered by this disclosure.

[0029] It should also be understood that, in the following description, direct connections or couplings between any functional blocks, devices, components, or other physical or functional units shown in the figures or described herein may also be achieved through indirect connections or couplings. Furthermore, it should be understood that functional blocks or units shown in the figures may be implemented as independent features or components in one embodiment, and may also be implemented wholly or partially in common features or components in another embodiment.

[0030] As used herein, the terms "workpiece" and "workpiece support" are used to indicate that a workpiece will be used in operation, while a workpiece support is used to hold and position the workpiece. Furthermore, ion implantation systems can be manufactured with workpiece supports configured to hold the workpiece, but these are typically not manufactured or sold with the workpiece. Therefore, discussions of the workpiece and how the beams or components of the ion implantation systems disclosed herein relate to the workpiece should also be understood as disclosures from the perspective of the workpiece support. The term "workpiece target" is used herein for the workpiece (if the workpiece is positioned on the workpiece support) or to indicate a position where the workpiece is configured to be held by the workpiece support.

[0031] Most conventional ion implantation systems require highly uniform dose. Variations in dose distribution can be achieved by changing the beam velocity to the workpiece target. Physical masks placed on the wafer itself can also be applied, but this is inefficient and costly in large-scale applications. This solution also lacks flexibility in creating different patterns. In contrast, the system and method disclosed herein are used to provide non-uniform doses to match specific ion implantation distributions. The desired predetermined dose distribution can be precisely replicated through multiple scans and the use of gated beamlines. The technique disclosed herein also allows for the realization of dose-free regions or regions with extremely large dose differences without using a physical mask on the workpiece target.

[0032] Such techniques can be used to mitigate the effects of spatial variations in one or more other process steps during semiconductor device manufacturing. For example, by varying the implantation dose to account for the corresponding spatial variations, the effects of non-uniform etch patterns can be at least partially compensated.

[0033] Ion implantation is a physical process (distinct from diffusion as a chemical process) used in semiconductor device fabrication to selectively implant dopants into semiconductor workpieces and / or wafer materials. Therefore, the implantation behavior does not depend on the chemical interaction between the dopant and the semiconductor material. In ion implantation, dopant atoms / molecules are ionized and separated, sometimes accelerated or decelerated, forming a beam that sweeps across the workpiece or wafer. Dopant ions physically bombard the workpiece, penetrate the surface, and typically remain within the crystal lattice structure beneath the workpiece surface.

[0034] Now refer to the attached diagram, Figure 1A This is a schematic diagram of an exemplary ion implantation system 100 according to one aspect of this disclosure. System 100 is presented for context and illustration purposes, and it should be understood that aspects of the invention are not limited to the described ion implantation system, and other suitable ion implantation systems with various configurations may also be employed.

[0035] System 100 includes a terminal 102, a beam assembly 104, and a terminal station 106. Terminal 102 includes an ion source 108 powered by a high-voltage power supply 110, which generates an ion beam 112 of selected species and directs it to the beam assembly 104. The ion source 108 generates charged ions, which are extracted and formed into the ion beam 112, which is directed along a beam path in the beam assembly 104 to the terminal station 106.

[0036] To generate ions, a dopant gas (not shown) to be ionized is located within the ion generation chamber 114 of the ion source 108. The dopant gas can be fed into the ion generation chamber 114, for example, from a gas source (not shown). In addition to the power source 110, it should be understood that one or more suitable mechanisms (not shown) can be used to excite free electrons within the ion generation chamber 114, such as an RF or microwave excitation source, an electron beam injection source, an electromagnetic source, and / or a cathode that generates an arc discharge within the chamber. The excited electrons collide with dopant gas molecules, thereby generating ions. Positive ions are typically generated, but the disclosure herein also applies to systems in which negative ions are generated.

[0037] In this example, ions are controllably extracted via slit 116 of ion generation chamber 114 through ion extraction assembly 118. Ion extraction assembly 118 includes multiple extraction and / or suppression electrodes 120a, 120b. Ion extraction assembly 118 may include, for example, a separate extraction power source (not shown) to bias extraction and / or suppression electrodes 120a, 120b, thereby accelerating ions from ion generation chamber 114. It should be understood that since ion beam 112 comprises particles with the same charge, the ion beam may have a tendency to expand radially outward when particles with the same charge repel each other. It should also be understood that in low-energy, high-current (high conductivity) beams, beam expansion is exacerbated, where many particles with the same charge (e.g., high current) move relatively slowly in the same direction (e.g., low energy), resulting in a large amount of repulsive force between the particles, but the particle momentum is too small to keep the particles moving in the direction of the beam path. Therefore, the ion extraction assembly 118 is typically configured such that the beam is extracted at high energy, preventing excessive beam expansion (e.g., ensuring the particles have sufficient momentum to overcome repulsive forces that could cause beam expansion). Furthermore, in this example, the beam 112 is typically transmitted at relatively high energy throughout the system 100 and decreases just before the workpiece 122 is held on the workpiece support 175 located in the terminal station 106 to facilitate beam confinement. In this case, the workpiece target is the location of the workpiece 122 or the location configured to be situated on the workpiece support 175.

[0038] exist Figure 1A In this example, the beamline assembly 104 includes a beam guide 124, a mass analyzer 126, a scanning system 128, and a parallelizer and / or corrector assembly 130 (collectively referred to as the parallelizer). The mass analyzer 126 performs mass analysis and angle correction / adjustment on the ion beam 112. In this example, the mass analyzer 126 is formed at approximately a 90-degree angle and includes one or more magnets (not shown) for establishing a (dipole) magnetic field therein. When the beam 112 enters the mass analyzer 126, it is accordingly bent by the magnetic field, thereby rejecting ions with inappropriate charge-to-mass ratios. More specifically, ions with excessively high or low charge-to-mass ratios are deflected into the sidewalls 132 of the mass analyzer 126. In this way, the mass analyzer 126 primarily allows those ions in the beam 112 with the desired charge-to-mass ratio to pass through it and exit through the resolving aperture 134 of the mass resolving aperture assembly 136, the details of which will be discussed further below.

[0039] The mass analyzer 126 can perform angular correction on the ion beam 112 by controlling or adjusting the amplitude of the magnetic dipole field. This adjustment of the magnetic field causes selected ions with the desired / selected charge-to-mass ratio to travel along different or altered paths. As a result, the resolution aperture 134 can be adjusted according to the altered path. In one example, the mass resolution aperture assembly 136 can be moved in the x-direction (e.g., transverse to the ion beam 112) to accommodate the altered path through the resolution aperture 134.

[0040] It should be understood that collisions between the ion beam 112 and other particles in system 100 can reduce beam integrity. Therefore, one or more pumps (not shown) may be included to at least evacuate the beam guide 124 and the mass analyzer 126.

[0041] The scanning system 128 in the illustrated example includes a magnetic scanning element 138 (also known as an ion beam scanner, which may be magnetic or electrostatic in the embodiment) and a focusing and steering element 140. Corresponding power supplies 142, 144 are operatively coupled to the magnetic scanning element 138 and the focusing and steering element 140, and more specifically, to corresponding electromagnets 146a, 146b and electrodes 148a, 148b located therein.

[0042] Focusing and steering element 140 receives a mass-analyzed ion beam 112 (e.g., a "pencil" beam) with a relatively narrow profile. A voltage applied by power supply 144 to electrodes 148a and 148b is used to focus and steer the beam to the scanning vertex 150 of magnetic scanning element 138. In this example, a voltage waveform applied by power supply 142 (which may be the same power supply as 144) to electromagnets 146a and 146b subsequently scans the beam 112 back and forth, thus defining the scanned ion beam 152 (sometimes referred to as a "strip beam"). It can be understood that scanning vertex 150 can be defined as a point in the optical path from which each sub-beam or scanned portion of the ion beam 112 appears to originate after scanning by magnetic scanning element 138.

[0043] The scanned ion beam 112 then passes through a parallelizer 130, which in the illustrated example comprises two dipole magnets 154a and 154b. For example, the two dipole magnets 154a and 154b are substantially trapezoidal and oriented as mirror images of each other, causing the beam 112 to bend into a substantially S-shape. In other words, the two dipole magnets 154a and 154b have equal angles and radii and opposite directions of curvature.

[0044] The parallelizer 130 alters the path of the scanned ion beam 112, ensuring that the ion beam travels parallel to the beam axis regardless of the scanning angle. As a result, the injection angle is relatively uniform across the entire workpiece 122.

[0045] In this example, one or more deceleration stages 156 are located downstream of the parallelizer 130. Up to this location in system 100, the ion beam 112 is typically transmitted at a relatively high energy level to mitigate the tendency for beam bulging, which can be particularly high where beam density increases (e.g., at scan apex 150). For example, one or more deceleration stages 156 include one or more electrodes 158a, 158b operable to decelerate the beam 112. The one or more electrodes 158a, 158b are typically apertures through which the ion beam 112 travels and... Figure 1A It can be drawn as a straight line.

[0046] However, it should be understood that although two electrodes 120a and 120b, electromagnets 146a and 146b, electrodes 148a and 148b, and 158a and 158b are shown respectively in the exemplary ion extraction assembly 118, magnetic scanning element 138, focusing and steering element 140, and deceleration stage 156, these elements may each include any suitable number of electrodes arranged and biased to accelerate and / or decelerate ions, and to focus, bend, deflect, converge, diverge, scan, parallelize, and / or purify the ion beam 112, as provided, for example, in U.S. Patent No. 6,777,696 to Rathmell et al., the entire contents of which are incorporated herein by reference. Furthermore, the focusing and steering element 140 may include electrostatic deflection plates (e.g., one or more pairs), and single lenses, quadrupoles, and / or other focusing elements to focus the ion beam.

[0047] Then, terminal station 106 receives the ion beam 112 guided toward workpiece 122. It should be understood that different types of terminal stations 106 can be used in the ion implantation system 100. For example, a "batch" type terminal station can simultaneously support multiple workpieces 122 on a rotating workpiece support structure, wherein the workpieces 122 are rotated along the beam path 160 (also called the beamline) of the ion beam 112 until all workpieces are fully implanted. On the other hand, a "serial" type terminal station supports a single workpiece 122 along the beam path 160 for implantation, wherein multiple workpieces are implanted one at a time in a serial manner, each workpiece being fully implanted before the next workpiece begins implantation. In a hybrid system, workpiece 122 can be mechanically translated in a first direction (the y-direction or the so-called "slow scan" direction) while the ion beam 112 scans in a second direction (the x-direction or the so-called "fast scan" direction) to cover the entire workpiece 122 with the ion beam 112.

[0048] In one example, the workpiece support 175 is coupled to a mechanical beam-to-workpiece translation system that moves the workpiece 122 relative to the beam 112 in the x-direction, y-direction, or x and y-direction. This is an alternative to a beam-to-workpiece translation system that scans the beam 112 in one or more dimensions of the workpiece 122. As described above, a hybrid system can also be used. For the purposes of this disclosure, whether scanning the beam 112 or moving the workpiece 122, the velocity and positioning of the beam 112 relative to the workpiece 122 (beam-to-workpiece velocity and position) are of primary concern.

[0049] The terminal station 106 in the illustrated example is a "serial" terminal station that supports a single workpiece 122 along beam path 160 for implantation. For example, a dose measurement system 162 is included in terminal station 106, near workpiece 122, for measuring the ion beam 112 (e.g., measurements can be performed prior to the implantation operation). During calibration, beam 112 passes through dose measurement system 162. For example, dose measurement system 162 includes one or more profilometers 164 that can continuously traverse profilometer path 166 to measure the profile of the scanned ion beam 152.

[0050] For example, one or more profilometers 164 may include a current density sensor, such as a Faraday cup, for measuring the current density of the scanned ion beam 152, where the current density is a function of the injection angle (e.g., the relative orientation between the ion beam and the mechanical surface of the workpiece 122, and / or the relative orientation between the ion beam and the lattice structure of the workpiece). For example, the current density sensor moves in a manner substantially orthogonal to the scanned ion beam 152, and thus typically spans the width of the scanned ion beam. In one example, the dose measurement system 162 measures both the beam density distribution and the angular distribution. The dose measurement system 162 may also measure the beam shape.

[0051] A control system 168 (also referred to as a controller) is also provided for controlling, communicating, and / or adjusting the ion source 108, mass analyzer 126, mass-resolved aperture assembly 136, magnetic scanning element 138, parallelizer 130, and dose measurement system 162. The control system 168 may include a computer, microprocessor, etc., and is operable to acquire measurements of the characteristics of the ion beam 112 and adjust parameters accordingly. The control system 168 may be coupled to the terminal 102 that generates the ion beam 112, as well as the mass analyzer 126, magnetic scanning element 138 (e.g., via power supply 142), focusing and steering element 140 (e.g., via power supply 144), and deceleration stage 156 of the beamline assembly 104. Thus, any of these elements can be regulated by the control system 168 to facilitate desired ion implantation.

[0052] According to examples of the technology disclosed herein, control system 168 controls the beam scanning speed to the workpiece target and the application of mechanical or other gating mechanisms. For example, while the beam / wafer scanning continues at a constant or varying speed, a dosimetry system 162 controlled by control system 168 can be used to gating (or blocking) the beam 112 at predetermined times during injection according to a desired injection profile.

[0053] If the measured beam current exceeds the tolerance range set in the process formulation for a specific ion implantation, the dose measurement system 162, controlled by the control system 168, can also be used to gate (or block) the beam 112 during implantation. For example, in a process formulation with a specified desired beam current of 20 mA and a predetermined range of ±10%, if the measured beam current is below 18 mA or above 22 mA, the control system 168 can be configured to close the resolving aperture assembly 136 to block and hold the implant.

[0054] Additional measurement systems (not shown, but similar to dose measurement system 162) can also be used in conjunction with dose measurement system 162 to detect rapid transients or glitches in beam 112 that might otherwise be undetectable by dose measurement system 162. For example, during a glitch, beam 112 is shut off, resolving aperture assembly 136 is closed or shielded, and the implanted material remains held until the ion beam stabilizes. For example, U.S. Patent No. 7,507,977 to Weiguo et al. describes a system and method for controlling an ion beam in response to an ion beam glitch.

[0055] The strength and direction of the magnetic fields(s) generated in the mass analyzer 126 can be adjusted, for example, by changing the charge-to-mass ratio of the beam by adjusting the amount of current flowing through the field winding therethrough. The injection angle can be controlled by adjusting the strength or amplitude of the magnetic fields(s) generated in the mass analyzer 126 in coordination with the mass resolving aperture assembly 136. In this example, the control system 168 can adjust the position of the magnetic fields(s) of the mass analyzer 126 and the resolving aperture 134 based on measurement data from the profilometer 164. The control system 168 can verify these adjustments via additional measurement data and, if necessary, perform additional adjustments via the mass analyzer 126 and the resolving aperture 134.

[0056] According to the techniques disclosed herein for providing a non-uniform dose distribution, the ion implantation system 100 includes a gating device for preventing the ion beam 112 from traveling further downstream toward the terminal station 106 or toward the workpiece 122. This can be achieved through a power-controlled gating device or a mechanical gating device. Another method of gating the beam away from the workpiece target is to change the beam energy so that it cannot reach the workpiece target, or to deflect the beam so that it no longer reaches the workpiece target. Deflection can be achieved through magnetic, electric, or electromagnetic beam deflection devices. The term "beam gating" as used herein includes this type of deflection, but more specifically it may be referred to as "beam parking."

[0057] exist Figure 1A In the example shown, the mechanical gating device is the resolving aperture assembly 136, which can be used to provide a rapid blocking motion for the resolving aperture 134 to gate (i.e., block or obstruct) the ion beam 112, preventing it from traveling further downstream toward the terminal station 106. As disclosed herein, during beam gating, the beam position to the workpiece target (which may be caused by beam scanning or workpiece / workpiece support movement) continues to change. This contrasts with fault detection, wafer placement, and other processes where the beam is gated and degated to maintain uniform dosage or to stop scanning motion to correct faults.

[0058] In the examples, at least two types of mechanical gating devices can achieve mechanical gating (or blocking) of the still-active ion beam 112: namely, a rotary shutter similar to a ball valve, and a resolving plate with one or more fixed-width apertures, wherein the desired aperture is typically located at the center of the beamline. These devices also have the advantage of allowing control over the width of the resolving aperture. An example of a porous plate is provided in U.S. Patent No. 7,399,980, co-owned by Vanderberg et al., the entire contents of which are incorporated herein by reference. This porous plate provides several resolving apertures of discrete widths, while also providing the ability to move the resolving apertures laterally to the ion beam to modify or correct the angular orientation of the ion beam.

[0059] In the example, according to the techniques disclosed herein, a single resolving aperture assembly 136 is configured to selectively gate (mask) the ion beam 112, preventing it from propagating outside the resolving aperture assembly 136. Furthermore, the resolving aperture assembly 136 can provide selective variation of the width of the resolving aperture 134 to selectively change the relative position of the resolving aperture across (e.g., laterally in the x-direction) and along (e.g., in the z-direction) the beam path 160.

[0060] Other devices used for beam gating include high-voltage fast switches on the power supply. These devices are faster than mechanical apertures or redirectors and are more precise in switching the beam on and off the workpiece.

[0061] Figure 1B An example of a power control gating device is disclosed. Figure 1B In an ion implantation system, an exemplary beam control circuit 200 is used to switch the extraction and / or suppression voltage in conjunction with the ion implantation system (such as...). Figure 1A The ion implantation system 100 uses an extraction and / or suppression electrode associated with an ion source to initiate or terminate the ion beam.

[0062] The beam control circuit 200 includes an extraction or suppression voltage source V 203, such as an extraction voltage VE or a suppression voltage VS, respectively. The beam control circuit 200 also includes a high voltage high speed (HVHS) switch 204 and a switch controller 208 for turning the high voltage high speed switch 204 on and off. The switch controller is connected between the voltage source 203 and the electrode 211 of the ion source 220, which is used to generate an amount of ions that can be extracted in the form of an ion beam.

[0063] The beam control circuit 200 also includes one or more parallel protection circuits 210 and / or series protection circuits 215, respectively, for absorbing energy from reactive components around the high-voltage high-speed switch 204 and protecting the switch from overvoltage damage. Protection circuits 210 and 215 also protect the high-voltage high-speed switch 204 and other components of the ion implanter by suppressing any ringing or other such overvoltages caused by switch transients and reactive components outside the high-voltage high-speed switch 204. The beam control circuit 200 can be used in any ion implanter, or other applications that may require beam control, or in circuits using, for example, a high-voltage power supply where arcing occurs at the electrodes or power output.

[0064] The beam control circuit 200 operates by receiving an external on / off command 208a, or by receiving a synchronous input command 208b from another such switch controller (switch circuit) to the switch controller 208. The switch controller 208 then closes the high-voltage, high-speed switch 204 before ion implantation begins to connect the voltage Va at electrode 211 of ion source 220 to the voltage Vb of voltage source 203 for ion beam generation. Subsequently, after ion implantation, the switch controller 208 reopens the high-voltage, high-speed switch 204. When the high-voltage, high-speed switch 204 is open, any overvoltage generated by the reactive components of the beam control circuit 200 is absorbed by protection circuits 210 and 215, and the voltage Va at electrode 211 drops to near zero, thereby terminating the ion beam. In this way, the beam control circuit 200 reduces the beam duty cycle or on-time of the ion beam in the ion implantation system.

[0065] In the example, the ion implantation system may have two such switches, one for extracting the power and the other for suppressing the power. These two switches can be synchronized by a switch controller 208.

[0066] Figure 1B The scheme features rapid times for starting and stabilizing the ion beam, which can be as fast as about 1 millisecond, or in other examples 0.75 milliseconds to 30 milliseconds, such as 0.8 to 10 milliseconds, or 0.9 to 3 milliseconds. Other switches and related systems and methods can be used for rapid gating of the ion beam on and off; for example, those disclosed in U.S. Patent 7,566,887, which is incorporated herein by reference. As described above, beam-stopping devices, such as electrical, electromagnetic, or magnetic deflection devices, can also be used.

[0067] In this and other ion implantation systems, the beam-to-target velocity can be variable. Some systems can change the beam scanning speed on the target. Other systems can change the beam-to-target velocity by altering the movement of the target / workpiece support while maintaining a static beam position. Some systems can change both the beam scanning speed and the movement of the target / workpiece support. The beam-to-target velocity can be modified incrementally depending on the system. Typically, the system's beam-to-target velocity can vary in 10% increments. The system's minimum velocity may be 1 / 10 of its maximum velocity.

[0068] Now for reference Figures 2 to 13 The methods related to gated ion implantation systems will be further described, starting with... Figures 2 to 11 It is described in detail using explanatory terminology, and then... Figure 12 and Figure 13 It is described in a more general overview form.

[0069] Figure 2 This is a graph comparing the desired dose distribution with the required beam velocity distribution to the workpiece target. The x-axis represents the wafer position, and the y-axis represents the relative dose and relative scan velocity. As a first example, Figure 2Consider a scenario where the desired dose distribution is a “notch.” Specifically, the dose at the notch is a percentage of the normal dose, for example, 10% (corresponding to 2.5 times the relative velocity), while the dose in the rest of the wafer is 90% (corresponding to 0.25 times the relative velocity), or the relative dose is reduced by 90%. This distribution can be achieved to obtain a 0.25 dose at the notch and a 2.5 relative dose in the non-notch area. This can be achieved by varying the beam velocity to the workpiece target, as shown in the figure. However, this requires a range of 1x minimum velocity and 10x maximum velocity. If this velocity variation exceeds the system bandwidth, the injection system will be unable to provide the desired dose distribution. Notably, even with multiple scans using this technique to attempt to approximate the desired distribution, the ratio of the lowest dose at the notch to the highest dose in the non-notch remains unchanged.

[0070] The techniques disclosed herein provide the ability to address situations where the desired dose distribution exceeds what an ion implantation system can achieve through variations in beam velocity to the workpiece target. This is to provide dose variations through multiple scans (the dose characteristics of a single scan are referred to as a “pattern”), including beam gating within the ion implantation system, to provide a predetermined dose distribution.

[0071] As another example of a desired distribution that cannot be achieved through conventional beam-to-target velocity variation, suppose the ion implantation system has the ability to sufficiently change the beam-to-target scanning velocity (e.g., 1 to 10 times), but cannot achieve the steep edges required in the distribution quickly enough. In this example, the techniques disclosed herein can be used to rapidly gate or deglide the ion beam while moving it only 0.05 mm (e.g., 0.06 to 1 mm, or 0.1 to 0.85 mm) from the beam to the target position. The beam can be gated or deglide in time, for example, as short as 1 millisecond (e.g., 2 to 10 milliseconds, or 3 to 5 milliseconds).

[0072] Figure 3 This is a graph showing the desired total dose distribution superimposed on the first pattern 302 and the second pattern 304, where the relative dose is on the y-axis and the wafer location is on the x-axis. In this case, the desired distribution in terms of total dose can be achieved using the techniques disclosed herein by combining the first pattern 302 with a beam or wafer that scans uniformly at maximum scan rate (providing 10% of the dose). The second pattern 304 provides a uniform beam-to-target velocity that provides 90% of the dose, but with a notch at the desired location caused by a gating mechanism. The gating mechanism (if it is a non-mechanical mechanism) can provide a steep notch in the distribution.

[0073] Figure 4This is a graph showing patterns 401-410, from the first to the tenth, where the relative dose is on the y-axis and the wafer position is on the x-axis. Each of the first to tenth patterns was run at the same scan rate. Figure 3 Assuming that the first pattern 302 and the second pattern 304 use different beams to reach the wafer at different velocities, this multi-velocity approach may not always be feasible or desirable. For example... Figure 4 As shown, the desired pattern can be achieved by a first uniform velocity pattern at 10% of the total dose (e.g., maximum velocity scan) and nine additional patterns having the same beam-to-target velocity with gating-induced notches.

[0074] The method disclosed herein can also generate distributions more complex than simple notches with steep sides. If the desired function is not notched, the notch width on each pattern can be varied by selective variable gating, thereby producing combined patterns that can replicate or approximate the desired dose function. Non-uniform beam-to-target scanning speed can be used to achieve certain effects in dose distribution, thereby varying the speed within a single scan pattern or between different scan patterns.

[0075] For example, Figure 5 A distribution of notches that approximates a linearly sloping edge is disclosed. Figure 5 Is with Figure 4 A similar graph shows patterns 501-510 from the first to the tenth, with relative dose on the y-axis and wafer position on the x-axis. The difference is that the gating mechanism is timed to activate and deactivate at different times in each pattern. The first pattern 501 provides a uniform scan rate and dose. Then, in successive scans 502-510, the gating is progressively advanced and delayed in the scan pattern (i.e., gating is turned on earlier and deactivated later). This provides a V-shaped notch in the ion implantation distribution, where the sides of the notch gradually narrow from a high dose (e.g., a cumulative relative dose of 1) at wafer positions 0 to 0.7 to a low dose (e.g., a cumulative relative dose of 0.1) at wafer positions 1 to 2. A second side of the notch rises at wafer position 2, returns to a high dose (cumulative relative dose of 1) at wafer position 2.3, and from there continues at a high dose to wafer position 3.

[0076] The wafer position described in this article can also be equated with the workpiece target position. Therefore, it can be seen that in the first and second scans (or subsequent additional scans), the ion beam can be gated by a gating device at the same workpiece target position or different workpiece target positions.

[0077] Figures 2 to 5The curves and distributions described are simplified representations assuming an ideal situation where the beam size is very small relative to the dose characteristics, but this is not usually the case in practice. The beam diameter in the scanning direction affects the notch shape. Therefore, if the beam shape is known, the actual dose pattern can be modeled, and the pattern width can be modified to produce a more realistic pattern that is closer to the desired pattern.

[0078] Figure 6 This is a graph showing the first to twentieth patterns 601-620, where the normalized dose is on the y-axis and the wafer location is on the x-axis. This example discloses the case of constructing a desired parabolic dose distribution using 20 patterns. Figure 6 In, with Figures 2 to 5 Similarly, beam shape is not considered, or the beam shape is assumed to be very small. The dose pattern here is determined by simply best fitting each pattern to the desired dose distribution (without considering beam shape). This simple pattern is a reasonable best choice for beams with small profiles in the mechanical scanning direction, such as sizes of 0.1 mm to 10 mm, 0.2 mm to 2 mm, or 0.5 mm to 1 mm. However, when using larger beams (e.g., 10 to 150 mm, 25 to 125 mm, or 50 to 100 mm), the proposed pattern loses accuracy in terms of actual dose.

[0079] Figure 7 This is a graph showing the first to twentieth patterns 701-720 using a 100mm beam, where the normalized dose is on the y-axis and the wafer position is on the x-axis. (Compared to...) Figure 6 compared to, Figure 7 The effect of using a larger beam diameter is shown. The actual dose becomes less accurate as the beam diameter increases, and... Figure 7 The ratio of the change in the mean to the expected parabola Figure 6 Larger. Specifically, the dose at the apex of the actual dose distribution is lower than the expected parabolic dose distribution, while the dose at the lowest part of the actual dose distribution (especially the trough) is larger than the expected parabolic dose distribution. This difference can be seen more clearly in Figure 8 . Figure 8 Is with Figure 7 A similar graph, but with the pattern removed, showing only the expected dose and predicted actual dose when using a 100mm beam.

[0080] In the above figures, the dose distribution is assumed to be a small beam, but Figure 9 , Figure 10 and Figure 11Beam size was taken into account. Compared to the figures above, the improvement in the expected dose versus the actual predicted dose was enhanced. To provide a better fit to the actual dose with the expected distribution, the beam shape effect can be modeled using various computational methods. Therefore, given the beam distribution, the best fit to the expected distribution can be determined using the calculated matrix solution. This effect can be exploited to achieve a smooth curve fit to the expected distribution by taking advantage of the blurring or smoothing properties of larger beams.

[0081] Figure 9 The diagram shows graphs of patterns 901-920, from the first to the twentieth, where the normalized dose is on the y-axis and the wafer position is on the x-axis. Surprisingly, to match the parabolic shape considering a 100mm beam diameter, the optimally fitted dose distribution requires two-step gating on each side of the notch. Here, patterns 901 to 906 are synchronized to be gated at the same moment during beam scanning, i.e., when the scan reaches approximately -55mm on the first side of the notch and approximately +55mm on the second side of the notch (where the 0 position is set in the middle of the notch). Patterns 907 to 920 are synchronized to be gated at the same moment during beam scanning, i.e., when the scan reaches approximately -55mm on the first side of the notch and approximately +55mm on the second side of the notch.

[0082] exist Figure 9 In this process, a set of scan patterns and gating timings are calculated using the following dose calculations to match the desired distribution.

[0083] The one-dimensional implantation dose at a point on the wafer can be predicted using the following equation: in: = Dose at point x = The expected instantaneous beam current density (in the x-direction), and any induced changes in the beam current, such as beam gating at a specified time or location. = The expected variation in beam-to-wafer velocity (in the x-direction), such as during continued scanning during beam-gated operation, or by changing the velocity with the beam current to modify the dose. = Electron charge If the wafer passes through the beam multiple times, the total dose is the sum of doses based on the above equation, where the beam current density and velocity distribution may vary as the wafer passes through: Where n defines the number of times the wafer passes through the beam each time, and includes the expected changes in beam density and beam velocity in each scan.

[0084] Then, based on the total dose at point x, the desired dose distribution in the x-direction can be calculated according to the above equation. This can be achieved using a method targeting... and An iterative solution method is used to determine the best fit with the desired dose distribution.

[0085] Figure 10 It shows that when such a product is produced... Figure 9 The ion implantation dose on the wafer is calculated after a set of patterns is shown.

[0086] Figure 11 Is with Figure 10 A similar graph, but with the pattern removed, shows only the expected dose 1102 and the empirically measured actual dose 1104 when using a 100mm beam. The actual observed dose 1104 was measured using sheet resistance (a well-known technique for measuring injected dose). In this way, the tight curve fit achieved using a large 100mm beam is superior to the curve fit achieved by considering only the beam shape (compared to...). Figure 8 Compare).

[0087] It should be noted that, although Figures 4 to 11 The example disclosed shows multiple scans with multiple uniform scan rates, but this is not necessary. Dose patterns and rates can be combined across the system bandwidth to provide greater flexibility.

[0088] Figures 2 to 11 Steeply notched dose distribution curves, V-shaped distribution curves with flat bottoms, and parabolic distribution curves are disclosed. Other shapes of distributions can also be implanted using the techniques disclosed herein. Other example distributions include symmetrical and asymmetrical U-shaped, V-shaped, wave-shaped, curved, and other asymmetrical distributions. The dose distribution can be repeated across the entire wafer as needed, i.e., repeated within the range of other workpiece target locations on the wafer. Various different dose distributions may be required for specific end applications.

[0089] Figure 12 This is a flowchart of an example method for performing ion implantation. In step 1210, an ion beam is generated. As previously mentioned, this can be achieved in various ways. It should be understood that these and other operations of the ion implantation system can be controlled by controllers operatively associated with the various components of the system.

[0090] In step 1220, the ion beam is moved relative to the workpiece target during the first scan, thereby moving the beam to the workpiece target position at a first beam-to-workpiece target velocity. To move the ion beam relative to the workpiece target position, the ion beam itself may move, or the workpiece / workpiece support may move.

[0091] In step 1230, during the first scan, the ion beam is gated while continuing to move towards the workpiece target position. Gating the ion beam refers to changing its on / off state and includes gating the ion beam to open, gating the ion beam to close, or both. As described above, gating can be achieved through electrical, magnetic, electromagnetic deflection (beam stopping), mechanical deflection, or power supply switching.

[0092] In step 1240, the ion beam is moved relative to the workpiece target in the second scan, thereby moving the beam-to-workpiece target position at a second beam-to-workpiece target velocity. The second scan covers the same area on the workpiece target as the first scan. That is, the second scan is superimposed on the first scan by additional ion implantation. The first and second beam-to-workpiece target velocities can be the same or different. Furthermore, the first or second beam-to-workpiece target velocity can be constant in a single scan or vary over the scan duration. The terms "first" and "second" are intended to describe the relative order between the two scans, not the absolute order. That is, the first scan mentioned herein is not necessarily the first time the workpiece target is scanned by the ion beam. There may be one or more earlier scans (whether or not gated).

[0093] In step 1250, during the second scan, the ion beam is gated while continuing to move the beam toward the workpiece target position. Furthermore, more than two scans can be performed, as illustrated in the numerous figures above. For example, 3 to 300 scans, 5 to 100 scans, or 10 to 25 scans can be performed to achieve the desired implantation distribution. Higher numbers of scan iterations can be used to provide more complex dose distributions and establish a larger total dose difference within the scanned region. For example, the dose change received at the first workpiece target position can be at least 25% greater than that at the second workpiece target position, which is closely adjacent to the first workpiece target position, i.e., at a distance of 0.05 mm, such as 0.06 to 1 mm, or 0.1 to 0.85 mm. This is limited by the beam height; for example, a beam height of 10 mm will result in a 10 mm transition region from 0% to 100% dose. In one example, this dose change can be 50% to 10,000%, 75% to 1,000%, or 75% to 250%. The method disclosed herein allows for a first workpiece target location with no dose, while an adjacent second workpiece target location receives a considerably large dose, such as 2 × 10⁻⁶. 13 Up to 1×10 14 ions / cm 2 For example, 3×10 13 Up to 8×10 13 , or 4×10 13 Up to 6×10 13 ions / cm 2The second target position can be closely adjacent to the first target position, i.e., the distance is 0.05 mm, for example, 0.06 to 1 mm, or 0.1 to 0.85 mm. Therefore, within a range of only 0.05 mm, the dose can vary, for example, by 5 × 10⁻⁶ from the first target position to the second target position. 13 ions / cm 2 The typical total dose for a workpiece is approximately 1 × 10⁻⁶. 15 (Equivalent to 20 scans), for example, 3×10 13 Up to 8×10 13 ions / cm 2 .

[0094] Figure 13 This is a flowchart of an example method for performing ion implantation. Figure 13 The focus is on the measurement and adjustment of the beam shape, as well as the calculation of a set of scanning patterns, to achieve a predetermined ion implantation dose.

[0095] In step 1310, an ion beam is generated. As previously mentioned, this can be achieved in a variety of ways.

[0096] In step 1320, the beam shape of the ion beam is measured. The beam shape should be known in order to properly time the gating to match the desired dose distribution. While a general beam shape can be obtained from standard settings, real-time beam monitoring, measurement, and adjustment can be performed on the ion implantation system if higher precision is required. In the example system, a multi-cup measuring device can be used to measure, monitor, and display the beam height and width. In the example, control software (e.g., software for providing a uniform implanted beam dose) can perform such analyses and bring the beam to a predetermined and consistent shape through a cyclic tuning process. This can be used to improve the process, for example, by reducing the number of scans or fine-tuning the precision.

[0097] In step 1330, the beam shape of the ion beam can be selectively adjusted to a predetermined beam shape. If the measured beam shape is within the expected parameter range, no adjustment is required. Furthermore, some ion implantation devices may not have the capability to adjust the beam shape. In this case, the measured beam shape remains unchanged and is taken into account through a gating process to achieve the desired implantation distribution in the next step.

[0098] In step 1340, a set of scan patterns, including gating timing, is calculated to match a predetermined ion implantation dose distribution, taking into account the measured (or adjusted and predetermined) beam shape. Examples of such calculations have been disclosed above. Control software can be used to instruct the controller to generate the set of scan patterns required to achieve the desired ion implantation dose distribution.

[0099] In step 1350, the set of scanning patterns is executed. This is achieved by multiple ion beam scans and by gating the beam on and off at appropriate times. The scanning patterns may also include variations in the beam-to-target velocity between different scanning patterns, or variations in velocity during a single scanning pattern.

[0100] While this disclosure has been shown and described for certain applications and implementations, it should be understood that equivalent substitutions and modifications will be conceived by those skilled in the art upon reading and understanding this specification and the accompanying drawings. In particular, regarding the functions performed by the various components (components, devices, circuits, systems, etc.) described above, unless otherwise stated, the terminology used to describe these components (including any reference to “device”) is intended to correspond to any component that performs the specified function of the said component (i.e., functionally equivalent), even if its structure is not structurally equivalent to the disclosed structure performing that function in the exemplary embodiments shown in this disclosure.

[0101] Furthermore, while a particular feature of this disclosure may be disclosed only for one of several embodiments, such a feature may be combined with one or more other features in other embodiments, which may be desirable and advantageous for any given or particular application. Moreover, with regard to the terms “comprising,” “including,” “having,” “having,” and variations thereof used in the detailed description or claims, such terms are intended to be interpreted as open-ended terms in a manner similar to the word “comprising.”

Claims

1. An ion implantation system, comprising: An ion source that generates ions and produces an ion beam along a beamline; A workpiece target, which is associated with the beamline; A controller configured to control a beam-to-workpiece target translation mechanism to move the ion beam relative to the workpiece target, thereby moving the beam-to-workpiece target position at a beam-to-workpiece target velocity; and A gate control device includes one or more of the following: Mechanical gating devices are configured to block or deflect ion beams so that they are not guided toward the workpiece target. A power control gating device configured to cut off the power supply to the ion source; or A magnetic, electromagnetic, or electric beam deflection device configured to deflect the ion beam so that it is not guided toward the workpiece target; The beam-to-workpiece target translation mechanism changes the position of the beam to the workpiece target while the ion beam is gated by the gating device.

2. The ion implantation system according to claim 1, wherein, The beam-to-workpiece target translation mechanism is as follows: Ion beam scanners based on electrostatics or magnetism; or A mechanical device for moving a workpiece target; and, The gating device includes one or more of the following: A mechanical gating device configured to block or deflect the ion beam, preventing it from being guided to the workpiece target; or A power control gating device configured to cut off the power supply to the ion source.

3. The ion implantation system of claim 1, further comprising a controller configured to cause the beam-to-target translation mechanism to perform a first scan and a second scan of the target.

4. The ion implantation system according to claim 3, wherein, The beam velocity to the workpiece target is uniform during the duration of the first and second scans.

5. The ion implantation system according to claim 3, wherein, The velocity of the beam to the workpiece target is not uniform during the duration of the first scan.

6. The ion implantation system according to claim 3, wherein, The beam velocity to the workpiece target is different for the first scan and the second scan.

7. The ion implantation system according to claim 3, wherein, In both the first and second scans, the ion beam is gated by the gating device at the same workpiece target location.

8. The ion implantation system according to claim 3, wherein, In the first and second scans, the ion beam is gated by the gating device at different workpiece target positions.

9. The ion implantation system of claim 1, further comprising a controller configured to cause the beam-to-target translation mechanism and the gating device to gate the ion beam when the beam moves 1 to 150 mm to the workpiece target position.

10. A method for performing ion implantation, comprising: Generate an ion beam; In the first scan, the ion beam is moved relative to the workpiece target, thereby moving the beam to the workpiece target position at a first beam-to-workpiece target velocity. as well as During the first scan, the ion beam is gated while continuing to move the beam to the workpiece target position.

11. The method of claim 10, further comprising: In the second scan, the ion beam is moved relative to the workpiece target, thereby moving the beam-to-workpiece target position at a second beam-to-workpiece target velocity, wherein the second scan covers the same workpiece target region as the first scan; as well as During the second scan, the ion beam is gated while continuing to move the beam to the workpiece target position.

12. The method according to claim 11, wherein, The gating of the ion beam in the second scan is performed at the workpiece target position by a beam that is different from the gating of the first scan.

13. The method of claim 10, further comprising, during the first scan, gating the ion beam off and gating the ion beam on.

14. The method of claim 10, wherein, During the first scan, the beam velocity to the workpiece target is constant.

15. The method according to claim 10, wherein, During the first scan, the beam velocity to the workpiece target is variable.

16. The method of claim 10, wherein, The dose change received at the first workpiece target position is at least 25% greater than that at the second workpiece target position, which is 0.05 to 1 mm away from the first workpiece target position.

17. The method according to claim 10, wherein, The first workpiece target position has no dose, the second workpiece target position has a dose, and the second workpiece target position is 0.05 mm away from the first workpiece target position.

18. The method of claim 11, further comprising calculating the timing of gating in the first and second scans to match a predetermined workpiece target dose distribution.

19. The method according to claim 18, wherein, When calculating the gating in the first and second scans to match the predetermined workpiece target dose distribution, the beam shape of the ion beam is taken into account.

20. The method according to claim 18, wherein, The predetermined workpiece target dose distribution is selected from the group consisting of the following symmetrical or asymmetrical shapes: notch, parabola, V-shape, U-shape, waveform, curve, and other asymmetrical shapes.

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