CN113496861B

CN113496861B - Ion implantation system

Info

Publication number: CN113496861B
Application number: CN202110191265.4A
Authority: CN
Inventors: 法兰克·辛克莱
Original assignee: Varian Semiconductor Equipment Associates Inc
Current assignee: Varian Semiconductor Equipment Associates Inc
Priority date: 2020-04-07
Filing date: 2021-02-20
Publication date: 2023-07-04
Anticipated expiration: 2041-02-20
Also published as: KR102544486B1; CN113496861A; TWI787739B; KR20210125413A; TW202139246A; JP2021177479A; JP7106698B2

Abstract

The present invention provides an ion implantation system comprising: an ion source; and a beam shaper that receives the continuous ion beam from the ion source and outputs a beam-shaped ion beam. The beam shaper may include a drift tube assembly having a grounded drift tube and an alternating current drift tube in alternating sequence. The drift tube assembly may include: a first grounded drift tube arranged to receive a continuous ion beam; at least two alternating current drift tubes downstream of the first grounded drift tube; and a second grounded drift tube downstream of the at least two alternating current drift tubes. The ion implantation system may include an ac voltage assembly coupled to the at least two ac drift tubes and including at least two ac voltage sources coupled to the at least two ac drift tubes, respectively. The ion implantation system may comprise a linear accelerator disposed downstream of the beam expander, the linear accelerator comprising a plurality of acceleration stages.

Description

Ion implantation system

RELATED APPLICATIONS

U.S. patent application Ser. No. 16/842,464, entitled "novel apparatus and technique for generating a beamed ion beam (NOVEL APPARATUS AND TECHNIQUES FOR GENERATING BUNCHED ION)" filed on even 7, month 4 of 2020, and entitled "novel apparatus and technique for generating a beamed ion beam (NOVEL APPARATUS AND TECHNIQUES FOR GENERATING BUNCHED ION BEAM)" filed on even 21, 2018, and incorporated herein by reference in its entirety, is hereby incorporated by reference.

Technical Field

The present disclosure relates generally to ion implantation equipment and, more particularly, to high energy beamline ion implanters.

Background

Ion implantation is a process of introducing dopants or impurities into a substrate via bombardment. An ion implantation system may include an ion source and a series of beamline components. The ion source may comprise a chamber that generates ions. The beamline components may include, for example, mass analyzers, collimators, and various components that accelerate or decelerate the ion beam. Much like a series of optical lenses used to manipulate the beam, the beamline assembly can filter, focus, and manipulate ion beams having particular materials, shapes, energies, and/or other qualities. The ion beam passes through the beamline assembly and may be directed toward a substrate mounted on a platen or clamp.

One type of ion implanter suitable for generating medium and high energy ion beams uses a linear accelerator or LINAC in which a series of electrodes arranged as a series of ducts around the beam accelerate the ion beam to higher and higher energies along a series of ducts. Each electrode may be arranged in the form of a series of stages, with a given electrode in a given stage receiving an AC voltage signal to accelerate the ion beam.

LINAC employs an initial stage that bunches an ion beam as the beam passes through a beamline. The initial stage of the LINAC may be referred to as a beam expander, wherein a continuous ion beam is received by the beam expander and output in packets as a beam-expanding ion beam. The reception or phase capture of an ion beam conducted through a known "double gap" beam expander using a supply electrode may be about 30-35% depending on the frequency and amplitude of the AC voltage signal, which means that 65% more of the beam current is lost when conducted to the accelerator stage of the linear accelerator.

The present disclosure is provided with respect to these and other considerations.

Disclosure of Invention

In one embodiment, an apparatus may include a multi-ring drift tube assembly including alternating sequence sets of grounded drift tubes and AC drift tubes arranged in an alternating manner with each other. The multi-ring drift tube assembly may further comprise: a first grounded drift tube arranged to receive a continuous ion beam; at least two AC drift tubes arranged in series downstream of the first grounded drift tube; and a second grounded drift tube downstream of the at least two AC drift tubes. The apparatus may further include an AC voltage component electrically coupled to the at least two AC drift tubes. The AC voltage component may comprise: a first AC voltage source coupled to deliver a first AC voltage signal to a first AC drift tube of the at least two AC drift tubes at a first frequency; and a second AC voltage source coupled to deliver a second AC voltage signal to a second AC drift tube of the at least two AC drift tubes at a second frequency. Thus, the second frequency may constitute an integer multiple of the first frequency.

In another embodiment, an ion implantation system may comprise: an ion source that generates a continuous ion beam; and a beam expander disposed downstream of the ion source to receive the continuous ion beam and output a focused ion beam. The beamformer may include a drift tube assembly characterized by alternating sequences of grounded and AC drift tube sets arranged in an alternating fashion with each other. The drift tube assembly may include: a first grounded drift tube arranged to receive a continuous ion beam; at least two AC drift tubes downstream of the first grounded drift tube; a second grounded drift tube downstream of the at least two AC drift tubes; and an AC voltage assembly electrically coupled to the at least two AC drift tubes. The AC voltage assembly may include at least two AC voltage sources coupled to at least two AC drift tubes, respectively. The ion implantation system may further comprise a linear accelerator disposed downstream of the beam expander, the linear accelerator comprising a plurality of acceleration stages.

In another embodiment, an apparatus may include a multi-ring drift tube assembly and an AC voltage assembly. The multi-ring drift tube assembly may include: a first grounded drift tube arranged to receive a continuous ion beam; and a first AC drift tube disposed adjacent to and downstream of the first grounded drift tube. The multi-ring drift tube assembly may further comprise: an indirectly ground drift tube arranged downstream of the first AC drift tube; and a second AC drift tube disposed adjacent to and downstream of the intermediate ground drift tube. The multi-ring drift tube assembly may also include a second grounded drift tube, wherein the second grounded drift tube is disposed adjacent to and downstream of the second AC drift tube. The apparatus may further include an AC voltage component electrically coupled to the multi-ring drift tube component. The AC voltage component may comprise: a first AC voltage source coupled to deliver a first AC voltage signal to the first AC drift tube at a first frequency; and a second AC voltage source coupled to deliver a second AC voltage signal to the second AC drift tube at a second frequency, wherein the second frequency comprises an integer multiple of the first frequency.

Drawings

The figures are not necessarily drawn to scale. The drawings are merely representative and are not intended to depict specific parameters of the disclosure. The drawings are intended to depict exemplary embodiments of the disclosure, and therefore should not be considered as limiting in scope. In the drawings, like numbering represents like elements.

Fig. 1A illustrates an exemplary ion implantation system according to an embodiment of the present disclosure.

Fig. 1B illustrates another ion implantation system according to an embodiment of the present disclosure.

Fig. 2 illustrates an exemplary beamformer in accordance with an embodiment of the present disclosure.

Fig. 3 illustrates another exemplary buncher in accordance with other embodiments of the present disclosure.

Fig. 4 depicts modeled results of operation of a drift tube assembly according to an embodiment of the present disclosure.

Fig. 5A and 5B are graphs showing the phase behavior of different ion beam rays processed by different beamformers, highlighting the benefits of embodiments of the present invention.

Fig. 6 depicts an exemplary process flow according to some embodiments of the present disclosure.

Fig. 7 illustrates another exemplary buncher in accordance with other embodiments of the present disclosure.

Fig. 8 illustrates another exemplary buncher in accordance with other embodiments of the present disclosure.

Fig. 9 illustrates yet another exemplary buncher in accordance with other embodiments of the present disclosure.

Fig. 10 shows a sawtooth waveform.

Description of the reference numerals

100. 100A: an ion implantation system;

102: an ion source;

106: an ion beam;

107: a gas box;

108: a DC accelerator column;

109: accelerating the ion beam;

109A: bunching;

109A1: a rear end;

109A2: a front end;

109B: a bag;

110: an analyzer;

111: an upstream beamline;

114. 212: a linear accelerator;

115: a high energy ion beam;

116: a filter magnet;

118: a scanner;

120: a collimator;

122: a terminal station;

124: a substrate;

126: an accelerator table;

130. 160, 200, 220, 230: a buncher;

140. 162, 166: an AC voltage component;

142. 214: a first AC voltage supply;

144. 216: a second AC voltage supply;

146: a third AC voltage supply;

148: an adder;

149: synthesizing an AC voltage signal;

150. 170, 201, 221, 232: a drift tube assembly;

152. 182, 202, 234: a first grounded drift tube;

154. 190, 210: a second grounded drift tube;

156. 180, 203: an AC drift tube assembly;

158. 192: accelerating a workbench;

164: a controller;

184. 186, 188, 204, 208: an AC drift tube;

206: a drift tube indirectly connected to the middle;

234: a first grounded drift tube;

236: a first AC drift tube;

238: a first indirectly grounded drift tube;

240: a second AC drift tube;

242: a second indirectly drift tube;

244: a third AC drift tube;

246: a second grounded drift tube;

600: a process flow;

602. 604, 606, 608: a frame;

l: a length;

V ₁ cos(ωt+φ ₁ )、V ₂ cos(2ωt+φ ₂ )、V ₃ cos(3ωt+φ ₃ ) AC: a voltage signal.

Detailed Description

Apparatuses, systems, and methods according to the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the systems and methods are shown. The systems and methods may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Instead, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the systems and methods to those skilled in the art.

As used herein, an element or operation recited in the singular and proceeded with the word "a/an" should be understood as also potentially encompassing plural elements or operations. Furthermore, references to "one embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

Methods for an improved high energy ion implantation system based on a beamline architecture are provided herein. For brevity, the ion implantation system may also be referred to herein as an "ion implanter". Various embodiments provide novel configurations for providing the capability to generate high energy ions, where the final ion energy delivered to the substrate may be 300 kilo-electron volts, 500 kilo-electron volts, 1 megaelectron volts, or more. In an exemplary embodiment, the novel beam expander design can be used to process an ion beam in a manner that increases ion beam acceptance, as described below.

Referring now to fig. 1A, an exemplary ion implanter, shown as implantation system 100, is depicted in block form. The ion implantation system 100 may represent a beamline ion implanter, with some elements omitted for clarity of illustration. The ion implantation system 100 may comprise an ion source 102 and a gas box 107 maintained at a high voltage as is known in the art. The ion source 102 may include an extraction assembly and a filter (not shown) to generate the ion beam 106 at a first energy. Examples of ion energies suitable for the first ion energy range from 5 kilo-electron volts to 100 kilo-electron volts, although the embodiments are not limited in this context. To form a high energy ion beam, the ion implantation system 100 includes various additional components for accelerating the ion beam 106.

The ion implantation system 100 may comprise an analyzer 110 for analyzing a received ion beam. Thus, in some embodiments, the analyzer 110 may receive the ion beam 106 with energy applied by extraction optics located at the ion source 102, where the ion energy is in the range of 100 kev or less than 100 kev, and specifically 80 kev or less than 80 kev. In other embodiments, the analyzer 110 may receive an ion beam accelerated by a DC accelerator column to a higher energy, such as 200 kev, 250 kev, 300 kev, 400 kev, or 500 kev. The embodiments are not limited in this context. The ion implantation system 100 may further comprise a beam shaper 130 and a linear accelerator 114 (shown in phantom) disposed downstream of the beam shaper 130. The operation of the beamformer 130 is detailed below. Briefly, the beam shaper 130 is disposed downstream of the upstream beamline 111 to receive the ion beam 106 as a continuous ion beam (or DC ion beam) and output the beam as a beamformed ion beam. In a beam-forming ion beam, the ion beam is output in discrete packets. At the same time, the energy of the ion beam may be increased by the beam shaper 130. The linear accelerator 114 may include a plurality of accelerator stages 126 arranged in series, as shown. The accelerator stage 126 may operate like a beam expander to output a beamed ion beam at a given stage and accelerate the ion beam to a higher energy in each stage. Thus, the beam shaper may be regarded as a first accelerator stage, which differs from a downstream accelerator stage in that it receives an ion beam as a continuous ion beam.

In various embodiments, the ion implantation system 100 may include additional components, such as a filter magnet 116, a scanner 118, and a collimator 120, wherein the general functions of the filter magnet 116, the scanner 118, and the collimator 120 are well known and will not be further detailed herein. Thus, after acceleration by the linear accelerator 114, the high energy ion beam represented by the high energy ion beam 115 may be delivered to an end station 122 for processing the substrate 124.

In some embodiments, where the ion beam 106 is provided directly to the analyzer 110, the beam shaper 130 may receive the ion beam 106 as a continuous ion beam of relatively low energy (e.g., less than 100 kilo-electron volts), as mentioned. In other embodiments, where the ion implantation system includes a DC accelerator column, the ion beam 106 may be accelerated to feed as a continuous ion beam at energies up to 500 kev or greater. In these different cases, the exact alternating current (alternating current, AC) voltage applied by the beam shaper 130 may be adjusted according to the ion energy of the continuous ion beam received by the beam shaper 130.

Fig. 1B illustrates an embodiment of an ion implantation system 100A comprising: a DC accelerator column 108 disposed downstream of the ion source 102 and arranged to accelerate the ion beam 106 to produce an accelerated ion beam 109 at a second ion energy, wherein the second ion energy is higher than the first ion energy produced by the ion source 102. The DC accelerator column 108 may be arranged in known DC accelerator columns, such as those used in medium energy ion implanters. The DC accelerator column may accelerate the ion beam 106 where the accelerated ion beam 109 is received by the analyzer 110 and the beam shaper 130 at energies such as 200 kev, 250 kev, 300 kev, 400 kev, or 500 kev. Otherwise, the ion implantation system 100A may function similarly to the ion implantation system 100.

Fig. 2 illustrates a structure of an exemplary beam shaper, shown as beam shaper 130, of a linear accelerator according to an embodiment of the present disclosure. The beam shaper 130 may include a drift tube assembly 150, the drift tube assembly 150 including a first grounded drift tube 152 arranged to receive a continuous ion beam, shown as an accelerated ion beam 109. As shown, the first grounded drift tube 152 is connected to an electrical ground. The drift tube assembly 150 may further include an AC drift tube assembly disposed downstream of the first grounded drift tube 152. As discussed in detail below, the AC drift tube assembly 156 is arranged to receive AC voltage signals, typically in the radio frequency range (RF range), that are used to accelerate and manipulate the accelerated ion beam 109. In the embodiment of fig. 2, the AC drift tube assembly 156 includes only one AC drift tube. In other embodiments, the AC drift tube assembly 156 may include a plurality of AC drift tubes.

The drift tube assembly 150 also includes a second grounded drift tube 154 downstream of the AC drift tube assembly 156. As a whole, the drift tube assembly 150 is arranged as a hollow cylinder to receive a continuous ion beam, conduct the ion beam through the hollow cylinder, and accelerate some portions of the ion beam and decelerate other portions in a manner that bundles the ion beam into discrete packets (shown as a bundle 109A) for receipt and further acceleration by an acceleration stage 158 located downstream. The drift tube assembly 150 may be constructed of graphite or similar suitable material configured to minimize contamination of the ion beam that is being conducted therethrough. The subsequent acceleration stage indicated by acceleration stage 158 may operate at a well-defined frequency ω, and capturing the beam into this acceleration structure may be limited by a phase angle of approximately ±5° with respect to this fundamental angular frequency ω. To transmit the maximum possible current through the entire beam line, the beamformer 130 needs to be arranged to produce one beamform for each period of this fundamental frequency ω.

As shown in fig. 2, the beamformer 130 also includes an AC voltage component 140, the AC voltage component 140 being arranged to send an AC voltage signal to the AC drift tube component 156 to drive a varying voltage at the powered drift tube of the AC drift tube component 156. The varying voltage across the AC drift tube assembly 156 provides different acceleration of ions depending on the arrival time of the ions at the AC drift tube assembly 156. In this way, the rear end 109A1 of the bunch 109A gives a greater rate than the front end 109A2 of the bunch 109A, and upon reaching the acceleration table 158, the entire bunch 109A becomes as compact as possible. In various embodiments, the AC voltage signal may be a composite of a plurality of individual AC voltage signals that are superimposed to produce the AC voltage signal by providing improved bunching of the continuous ion beam. In various embodiments, the AC voltage component 140 may generate a first AC voltage signal at a first frequency and a second AC voltage signal at a second frequency, wherein the second frequency comprises an integer multiple of the first frequency. In some embodiments, the AC voltage component 140 may generate a third AC voltage signal at a third frequency, where the third frequency constitutes an integer multiple of the first frequency and is different from the second frequency, and so on. Thus, the second frequency, the third frequency, etc. may be harmonics of the first frequency, wherein the frequencies may be two times, three times, etc. the first frequency.

In the embodiment of FIG. 2, an AC voltage component 140 is shown to generate three different AC voltage signals, denoted V ₁ cos(ωt+φ ₁ )、V ₂ cos(2ωt+φ ₂ ) V (V) ₃ cos(3ωt+φ ₃ ). For illustration purposes, the AC voltage signal is shown as a sinusoidal signal, but other waveform shapes are possible. The AC voltage component 140 may include a first AC voltage supply 142, a second AC voltage supply 144, and a third AC voltage supply 146 to generate a first AC voltage signal, a second AC voltage signal, and a third AC voltage signal, respectively. The AC voltage supply may be implemented using an RF amplifier driven by a synchronous signal generator. The generic term V refers to the maximum amplitude of the AC voltage signal, while the generic term phi refers to the phase of the AC voltage signal. Thus, the maximum amplitude and phase may be different between different signals. In this embodiment, the second AC voltage signal and the third AC voltage signal represent two and three times the frequency of the first signal ω, respectively. As shown in fig. 2, the AC voltage component 140 may include an adder 148, where the adder 148 sums the individual voltage signals and outputs a composite AC voltage signal 149 to an AC drift tube component 156.

In various embodiments, the composite AC voltage signal may be formed from an AC voltage signal, wherein the highest frequency of the AC voltage signal is approximately 120 megahertz or less than 120 megahertz.

The composite AC voltage signal 149 is designed to adjust the phase dependence of ions processed by the AC drift tube assembly 156 in a manner that increases reception at the downstream acceleration stage. In known linear accelerators of ion implantation systems, when a continuous ion beam is transported in packets through a beam-forming process to a downstream acceleration stage, a certain portion of the ion beam is lost against walls or other surfaces due to the nature of the acceleration and beam-forming process. Reception refers to the percentage of the ion beam that is not lost (e.g., the percentage of beam current) and is therefore received by the downstream acceleration stage. As mentioned, in known ion implantation apparatus employing a linear accelerator, the reception can be about 30% to 35% at maximum when various conditions are optimized. Such known ion implantation systems may drive the beam expander with an AC voltage signal having a frequency of 10 mhz, 13.56 mhz, or 20 mhz, and a voltage amplitude in the tens of kilovolts range. Notably, AC voltage signals in known ion implantation systems may be generated as simple AC voltage signals of a single frequency.

Notably, the fundamental component of the composite AC voltage signal can be simplified to V ₁ cos (ωt) in which the relative phases with respect to the other two AC voltage signals are shifted by a corresponding phase shift φ ₂ Or phi ₃ Given. As described in detail below, these offsets may be adjusted to increase reception.

In particular, the inventors have found that applying multiple frequencies to produce a complex (complex waveform) yields better output phase coherence/acquisition than known beamformers employing single frequency AC voltage signals.

Turning to fig. 3, a structure of an exemplary beam condenser (beam condenser 160) of a linear accelerator according to other embodiments of the present disclosure is shown. The beam shaper 160 may include a drift tube assembly 170 that includes a first grounded drift tube 182 arranged to receive a continuous ion beam, shown as an accelerated ion beam 109. As shown, the first grounded drift tube 182 is connected to an electrical ground. The drift tube assembly 170 may further include an AC drift tube assembly 180 disposed downstream of the first grounded drift tube 182. As discussed in detail below, similar to the AC drift tube assembly 156, the AC drift tube assembly 180 is arranged to receive AC voltage signals, typically in the radio frequency range (RF range), that are used to accelerate and manipulate the accelerated ion beam 109. In the embodiment of fig. 3, AC drift tube assembly 180 includes three AC drift tubes, shown as AC drift tube 184, AC drift tube 186, and AC drift tube 188.

The drift tube assembly 170 also includes a second grounded drift tube 190 downstream of the AC drift tube assembly 180. As a whole, the drift tube assembly 170 is arranged as a hollow cylinder to receive a continuous ion beam, conduct the ion beam through the hollow cylinder, and accelerate the ion beam in a manner to bunch the ion beam into discrete packets (shown as bunches 109A) for receipt and further acceleration by an acceleration stage 192 located downstream. Thus, the drift tube assembly 170 may constitute a multi-ring drift tube assembly having a length (in the direction of propagation of the ion beam) of at least 100 millimeters and less than 400 millimeters.

In the embodiment of fig. 3, an AC voltage component 162 is provided that is arranged to send an AC voltage signal to the AC drift tube component 180 to drive a varying voltage at the powered drift tube of the AC drift tube component 180. The AC voltage component 162 may be configured with the first AC voltage supply 142 driving the AC drift tube 184, the second AC voltage supply 144 driving the AC drift tube 186, and the third AC voltage supply 146 driving the AC drift tube 188. These AC voltage signals may be synchronized in time by the controller 164 to effectively generate a composite signal similar to the composite AC voltage signal 149. Although fig. 3 shows a configuration in which the lowest frequency AC voltage signal is supplied to the furthest upstream AC drift tube, in other embodiments, the lowest frequency AC voltage signal (V ₁ cos(ωt+φ ₁ ) To different AC drift tubes). The above applies to the intermediate frequency AC voltage signal (V ₂ cos(2ωt+φ ₂ ) And a high frequency AC voltage signal (V) ₃ cos(3ωt+φ ₃ )). This configuration has advantages over the configuration in fig. 2 in that the power supply risk of disturbing other power supplies is avoided.

While it is possible to use a multi-frequency AC voltage signal to drive the beamformer, it is noted that the use of multiple frequencies to generate the AC voltage signal may entail a larger voltage supply and may result in a longer beam line, as described in more detail below. Thus, such a configuration in a beamline ion implanter has not been contemplated so far. Notably, the inventors have identified arrangements that can overcome these considerations by adjusting the drive signal to significantly improve ion beam throughput, particularly for ions having masses in the range of common dopants (e.g., boron, phosphorus, and the like). Specifically, in the "single loop" (where "loop" refers to an AC drift tube) beamer of fig. 2 or the "three loop" beamer of fig. 3, a composite AC voltage signal is generated in which the beaming of the ion beam is performed in a manner that improves phase coherence by using the ion beam at a target distance from the AC drift tube assembly, and thus increases reception.

Turning to fig. 4, a composite description is shown containing a plot of the drift tube assembly 150 and the corresponding phase map (showing distance function in millimeters along the beam path). The phase diagram is a graph showing the phase (shown on the right ordinate) as a function of distance, with the position of the individual drift tubes of the AC drift tube assembly 156 extending between 30 and 75 millimeters. At this location, the voltage applied to the AC drift tube assembly 156 (shown by the left ordinate) reaches a maximum of approximately 18 kv and is applied at a frequency of 40 mhz. The right side of the graph shows the relative phase positions of a series of 21 different rays of the accelerated ion beam 109. The ion mass of the accelerated ion beam 109 is assumed to be 20amu. As shown, the voltage reaches a maximum at the location of the AC drift tube assembly 156 and is zero elsewhere. At the entry point into the AC drift tube assembly 156, the 21 exemplary rays are equally spaced in phase at 18 degree intervals. When passing through a pass v=v as generated by AC voltage component 140 ₁ cos(ωt+φ ₁ )+V ₂ cos(2ωt+φ ₂ )+V ₃ cos(3ωt+φ ₃ ) When the given composite AC voltage signal is processed, the individual rays converge to the right in phase, as shown.

At a position of 700 mm, 670 mm corresponding to the right side of the inlet of the AC drift tube assembly 156, the phase difference between many rays approaches zero. Thus, the reception may be a maximum when the entrance of the acceleration table 158 is positioned at a 700 millimeter position (corresponding to zero phase difference between many rays). For reception based on a +/-5 degree variation, in the example of fig. 4, the reception at the accelerator is approximately 55%. In various other simulations, the maximum acceptance of the configuration of fig. 4 has been calculated to be as high as 75% with a significant improvement over 30% to 35% acceptance of known ion implanters employing a single frequency beam expander. For example, when V is set equal to 59.4 kv, 75% is received, and at 24 kv, 65% is received.

Notably, the same behavior of the illustrated phase convergence using the AC drift tube assembly 156 shown in fig. 4 can be obtained by applying the same voltage parameters to the three-ring configuration of the AC drift tube assembly 180.

Fig. 5A and 5B are graphs showing phase behavior of different rays of an ion beam highlighting the benefits of applying a composite AC voltage signal according to an embodiment of the present invention. Fig. 5A continues the composite AC voltage parameters of the embodiment of fig. 4, while fig. 5B shows an example of a simple AC voltage signal being applied to the ion beam. In the illustration of fig. 5B, the AC signal is derived by: v=v _max cos (ωt+Φ), whereas in fig. 5A, the AC signal is derived by: v=v ₁ cos(ωt+φ ₁ )+V ₂ cos(2ωt+φ ₂ )+V ₃ cos(3ωt+φ ₃ ). In both cases, the frequency ω is 40 megahertz.

In two different graphs, the phase behavior depicts the phase of a given ray at a specified distance from a point near the entrance to the beamformer as a function of the phase of the given ray at the entrance to the beamformer. The specified distance is set at a distance where the phases of the different rays of the ion beam can be conveniently converged. Thus, referring again to fig. 4, in bunching 109A, operation of AC drift tube assembly 156 tends to accelerate the phase-retarded ions (trailing end 109A 1) and tends to decelerate the phase-leading ions (leading end 109A 2), causing phase convergence at, for example, 700 millimeters.

In fig. 5B, most of the phase coherence conditions produce a highest relative reception of 35%, even though the initial phase difference is only 30 degrees, there is still a small degree of phase difference at 400 millimeters. As shown, the behavior is worse for other voltages. Notably, the embodiment of fig. 5A produces a convergence at 700 millimeters that is slightly longer than the single frequency beamformer result that would require convergence at 400 millimeters. This result is due in part to the need to maintain the AC voltage amplitude at a reasonable level for the composite AC voltage signal, such as approximately 20 kv. In the case of a single frequency beamformer, operation at an AC voltage amplitude of 20 kv causes convergence at 400 mm. While the embodiment of fig. 5A may entail a slightly longer spacing between the beamer and accelerator (700 millimeters versus 400 millimeters) as compared to a single frequency beamer architecture, the benefit is substantially greater reception and thus beam current flow is conducted into the main accelerator stage of the LINAC. In various additional embodiments, the aggregate length may be in the range of 300 millimeters to 1000 millimeters.

Without being limited to a particular theory, the above results may be explained in the following manner. Applying multiple frequencies to produce a composite or composite AC voltage signal (waveform) may produce a waveform having a shape that is more conducive to progressively increasing capture. In principle a wave form with sharp features, such as a vertical saw tooth shape, as shown in fig. 10. The waveform accelerates ions in a manner that "serrations" the ions together to form a cluster, theoretically achieving about 100% trapping. Notably, in practical beamformers, resonators based on resonant circuits are used to drive AC voltage waveforms at relevant frequencies (in the megahertz range), where the resonant circuits themselves produce sine waves, which do not produce high capture as in the vertical saw tooth case. In the inventive method, a plurality of sinusoidal waveforms of different frequencies are added for generating a composite waveform that may exhibit a shape that is closer to the ideal sawtooth shape, and thus increase improved output phase coherence and acquisition, as described above.

It should be noted that in embodiments of the present invention, two or more waveforms may exhibit a relationship that produces a first waveform at a fundamental frequency and another waveform at an integer multiple of the fundamental frequency. In this way, when the new component is at an integer multiple of the fundamental frequency, each ion beam will experience the same field, and the fundamental highest common factor frequency remains unchanged at the fundamental frequency.

While adding a large number of waveforms, such as Fourier series (Fourier series), in principle, may produce a composite waveform that more closely approximates the synthesis of a sawtooth waveform, such an approach may be impractical due to the increased cost of adding such a large number of frequencies. The inventors have found that adding only two or three harmonics of the sinusoidal waveform produces a very significant increase in output phase coherence and capture, as discussed above. In addition, the inventors have found that applying different sinusoidal waveforms to separate electrodes can operate similarly to applying different sinusoidal waveforms to a single electrode, and that applying only two waveforms produces significant improvements in output phase coherence and acquisition, as opposed to the relatively lower output phase coherence produced by a single frequency waveform, as is the case with three waveforms.

Although the additional stages of the LINAC may accelerate and further beam ion packets in a similar manner to the beam shaper of an embodiment of the present invention, these additional stages of the LINAC need not be driven by a composite AC voltage signal as shown. In other words, since the composite AC voltage signal of the beam shaper has focused a large portion of the various rays of the beamformed ion beam at the entrance to the accelerator table, it may be less necessary to further enhance the phase convergence. This fact allows a simpler design of the AC voltage component to drive the accelerator table of the LINAC.

As an example, in one embodiment of a triple frequency composite AC signal, the fundamental frequency of the first signal may be 40 megahertz, while the first harmonic frequency of the second signal added to the first signal may be 80 megahertz, and the second harmonic frequency of the third signal added to the first and second signals may be 120 megahertz.

It is noted that while the above embodiments emphasize that the composite AC voltage signal is generated based on three AC voltage signals and employs a multi-ring drift tube assembly that includes three drift tubes, in other embodiments the composite AC voltage signal may be formed from two AC voltage signals or four AC voltage signals. The embodiments are not limited in this context. Likewise, multiple ring drift tube assemblies according to other embodiments may employ two drift tubes or four drift tubes. The embodiments are not limited in this context.

Fig. 6 depicts an exemplary process flow 600 according to some embodiments of the present disclosure. At block 602, an ion beam is generated as a continuous ion beam, such as by extraction from an ion source. Thus, the ion beam may exhibit ion energies in the range of several keV up to approximately 80 kilo-electron volts. Optionally, the continuous ion beam may be accelerated to produce an accelerated continuous ion beam. In one example, a DC accelerator column may be applied to accelerate the continuous ion beam. Thus, in some embodiments, the accelerated continuous ion beam may exhibit ion energies of 200 kilo-electron volts to 500 kilo-electron volts or more.

At block 604, a continuous ion beam is received in a multi-ring drift tube assembly. The multi-ring drift tube assembly may include a first grounded drift tube and a second grounded drift tube, and a multi-ring AC drift tube assembly disposed between the first grounded drift tube and the second grounded drift tube.

At block 606, the continuous ion beam is conducted through a first AC drift tube of the multi-ring drift tube assembly while a first AC voltage signal is applied to the first AC drift tube at a first frequency.

At block 608, the continuous ion beam is conducted through a second AC drift tube of the multi-ring drift tube assembly while applying a second AC voltage signal to the second AC drift tube at a second frequency. In various embodiments, the second frequency may be an integer multiple of the first frequency, such as twice the first frequency. In an optional operation, the accelerated continuous ion beam may be conducted through a third AC drift tube of the multi-ring drift tube assembly while a third AC voltage signal is applied to the third AC drift tube at a third frequency. The third frequency may be an integer multiple of the first frequency and different from the second frequency. Thus, an accelerated continuous ion beam may be output from the multi-ring drift tube assembly as a beamformed ion beam.

Fig. 7 illustrates another exemplary beamer (beamer 200) for a linear accelerator according to other embodiments of the present disclosure. The beam shaper 200 may include a drift tube assembly 201, the drift tube assembly 201 including a first grounded drift tube 202 arranged to receive a continuous ion beam, shown as an accelerated ion beam 109. As shown, the first grounded drift tube 202 is connected to an electrical ground. The drift tube assembly 201 may further include an AC drift tube assembly 203 disposed downstream of the first grounded drift tube 182. Similar to the AC drift tube assemblies described previously, the AC drift tube assembly 203 is arranged to receive AC voltage signals, typically in the radio frequency range (RF range), that are used to accelerate/decelerate and manipulate the accelerated ion beam 109. In the embodiment of fig. 7, the AC drift tube assembly 201 includes two AC drift tubes, shown as AC drift tube 204 and AC drift tube 208.

The drift tube assembly 201 also includes a second grounded drift tube 210 downstream of the AC drift tube assembly 203. As a whole, the drift tube assembly 201 is arranged as a hollow cylinder to receive a continuous ion beam in a manner that bundles the ion beam into discrete packets (shown as packets 109B), conducting the ion beam through the hollow cylinder and accelerating/decelerating the ion beam for receipt and further acceleration by a downstream disposed linear accelerator 212. Thus, the drift tube assembly 201 may constitute a multi-ring drift tube assembly having a length (in the direction of propagation of the ion beam) of at least 100 millimeters and less than 400 millimeters.

In the embodiment of fig. 7, an AC voltage component 166 is provided and arranged to send an AC voltage signal to the AC drift tube component 203 to drive a varying voltage at the powered drift tube of the AC drift tube component 203. The AC voltage assembly 166 may be configured with a first AC voltage supply 214 driving the AC drift tube 204 and a second AC voltage supply 216 driving the AC drift tube 208. In this configuration and the configuration of fig. 8, two different AC voltage supplies may output a first frequency of 40 megahertz and a second frequency of 80 megahertz, or alternatively two different AC voltage supplies may output a first frequency of 13.56 megahertz and a second frequency of 27.12 megahertz according to different non-limiting embodiments.

These AC voltage signals may be synchronized in time by the controller 164 to produce beam behavior similar to that produced by a single drift tube through a composite signal given below: v=v ₁ cos(ωt+φ ₁ )+V ₂ cos(2ωt+φ ₂ ). In this way, the output phase coherence as a function of the input phase of the ions can be improved over a single frequency beamformer in a manner similar to the embodiments of fig. 2-5B (discussed above).

Although fig. 7 shows a configuration in which the lowest frequency AC voltage signal is supplied to the furthest upstream AC drift tube 204, in other embodiments, the lowest frequency AC voltage signal (V ₁ cos(ωt+φ ₁ ) To different AC drift tubes).

Fig. 8 illustrates another exemplary beamformer (beamformer 220) according to other embodiments of the present disclosure. The beam shaper 220 may include a drift tube assembly 221, the drift tube assembly 221 including a first grounded drift tube 202 arranged to receive a continuous ion beam, shown as an accelerated ion beam 109. As shown, the first grounded drift tube 202 is connected to an electrical ground. The drift tube assembly 221 may further include an AC drift tube 204 disposed downstream of the first grounded drift tube 202. In the embodiment of fig. 8, the AC drift tube 208 is disposed downstream of the AC drift tube 204, and the second grounded drift tube 210 is disposed downstream of the AC drift tube 208, as in the embodiment of fig. 7. Thus, the drift tube assembly 201 may constitute a multi-ring drift tube assembly having a length L (in the direction of propagation of the ion beam) of at least 100 millimeters and less than 400 millimeters. In addition to the foregoing components, the drift tube assembly 221 includes an indirectly drift tube 206 disposed between the AC drift tube 204 and the drift tube 208. This configuration provides the advantage of reducing the risk of crosstalk between the two power supplies (AC voltage supply 214, AC voltage supply 216) and the two resonant circuits driving the AC drift tube 204 and the AC drift tube 208, respectively.

The embodiment of fig. 8 shows a drift tube assembly 221 characterized by alternating AC drift tubes and grounded drift tubes in alternating order as the ion beam propagates down the beamline. In other embodiments of the alternating sequence, in addition to the grounded drift tubes disposed between each successive pair of AC drift tubes, three or more AC drift tubes may be provided to generate a composite AC signal, generally as described with respect to fig. 3. In this way, cross-talk between all power sources and the resonator can be cut down.

It should be noted that in embodiments using two frequencies of up to 200 degrees of output phase coherence, up to 55% ion beam reception may be obtained. In various embodiments, the conduit length of the drift tube may be adjusted by the following considerations: 1) The length may be adjusted according to the distance of ions in a given ion beam traveling at 180 °, or

Wherein the method comprises the steps ofv is the rate. This distance produces maximum acceleration for a given voltage, but may produce some undesirable phase effects. Using as low as 0.2D ₀ Will require higher voltages but will produce overall better results. With respect to the convergence length L, it is beneficial to make this parameter shorter, but a higher voltage needs to be applied. Thus, L may range from 300 millimeters to 1 meter based on ionic species, voltage considerations, and other impacts according to different embodiments.

It should also be noted that while applying a multi-frequency signal may generally be used to increase the aggregate length, when the design is limited to the highest voltage applied and subtracting individual frequencies, a particular multi-frequency design may be achieved without increasing the aggregate length.

Fig. 9 provides an example of such an arrangement, in which a beamformer 230 is shown. The drift tube assembly 232 includes: a first grounded drift tube 234; a first AC drift tube 236 disposed adjacent the first grounded drift tube 234 and downstream of the first grounded drift tube 234; a first intermediate ground drift tube 238 disposed downstream of the first AC drift tube 236; a second AC drift tube 240 disposed adjacent the first intermediate ground drift tube 238 and downstream of the first intermediate ground drift tube 238; a second indirectly drift tube 242 disposed adjacent to the second AC drift tube 240 and downstream of the second AC drift tube 240; a third AC drift tube 244 disposed adjacent to the second intermediate ground drift tube 242 and downstream of the second intermediate ground drift tube 242; and a second grounded drift tube 246, wherein the second grounded drift tube 246 is disposed adjacent to the third AC drift tube 244 and downstream of the third AC drift tube 244. Also, providing the first intermediate ground drift tube 238 and the second intermediate ground drift tube 242 may prevent crosstalk between the first AC voltage supply 142, the second AC voltage supply 144, and the third AC voltage supply 146.

In summary, embodiments of the present invention provide beamformers controlled using multi-frequency signals that are commonly applied to individual AC drift tubes or individually and individually to dedicated AC drift tubes. Although not limiting, various embodiments may employ commercially available frequencies as set forth in table I below.

Table I.

Table I above shows various ISM frequencies, as defined by the us FCC, where in embodiments of the present invention each frequency will be an integer multiple of the fundamental frequency applied to the signal. Thus, in a two-frequency embodiment, a combination of 13.56 megahertz and 27.12 megahertz is suitable, in a three-frequency embodiment, a combination of 13.56 megahertz and 27.12 megahertz and 40.68 megahertz is suitable, and so on.

In view of the foregoing, at least the following advantages are achieved by the embodiments disclosed herein. A first advantage is achieved by providing a composite AC voltage signal to drive the beam shaper such that substantially greater ion beam current may be transmitted through a downstream disposed LINAC. Another advantage is the ability to drive a given AC signal from a given one of the plurality of AC power sources to the dedicated electrode, avoiding interference between the power sources that may occur when coupled to a common multiple power source through the common electrode to drive multiple AC voltage signals, but still drive a larger ion beam current in the case of a composite AC voltage signal.

Although certain embodiments of the present disclosure have been described herein, the present disclosure is not so limited, as the present disclosure is as broad in scope as the art will allow, and the specification is to be read likewise. Accordingly, the above description should not be construed as limiting. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims

1. An ion implantation system, comprising:

an ion source that generates a continuous ion beam;

a beam expander disposed downstream of the ion source to receive the continuous ion beam and output a focused ion beam, wherein the beam expander comprises a drift tube assembly comprising:

a first grounded drift tube arranged to receive the continuous ion beam;

at least two alternating current drift tubes downstream of the first grounded drift tube;

a second grounded drift tube downstream of the at least two alternating current drift tubes; a kind of electronic device with high-pressure air-conditioning system

An alternating current voltage assembly electrically coupled to the at least two alternating current drift tubes, the alternating current voltage assembly comprising at least two alternating current voltage sources respectively coupled to the at least two alternating current drift tubes; and

A linear accelerator comprising a plurality of acceleration stages, the linear accelerator disposed downstream of the beam expander to receive and accelerate the beamed ion beam,

wherein the alternating current voltage assembly comprises:

a first alternating current voltage source coupled to deliver a first alternating current voltage signal to a first alternating current drift tube of the at least two alternating current drift tubes at a first frequency; and

a second alternating current voltage source coupled to deliver a second alternating current voltage signal to a second one of the at least two alternating current drift tubes at a second frequency, wherein the second frequency comprises an integer multiple of the first frequency,

wherein the beam shaper further comprises:

the first grounded drift tube;

the first alternating current drift tube disposed adjacent to and downstream of the first grounded drift tube;

an indirectly ground drift tube disposed downstream of the first alternating current drift tube;

the second alternating current drift tube is disposed adjacent to and downstream of the intermediate ground drift tube; and

the second grounded drift tube, wherein the second grounded drift tube is disposed adjacent to and downstream of the second alternating current drift tube.

2. The ion implantation system of claim 1, wherein the first frequency is 40 megahertz and the second frequency is 80 megahertz.

3. The ion implantation system of claim 1, wherein the first frequency is 13.56 megahertz and the second frequency is 27.12 megahertz.

4. The ion implantation system of claim 1, the buncher further comprising:

the first grounded drift tube;

the first alternating current drift tube, wherein the first alternating current drift tube is disposed adjacent to and downstream of the first ground drift tube;

a first indirectly ground drift tube disposed downstream of the first alternating current drift tube;

the second alternating current drift tube, wherein the second alternating current drift tube is disposed adjacent to and downstream of the first intermediate ground drift tube;

a second indirectly ground drift tube disposed adjacent to and downstream of the second alternating current drift tube;

a third alternating current drift tube disposed adjacent to and downstream of the second intermediate ground drift tube; and

the second grounded drift tube, wherein the second grounded drift tube is disposed adjacent to and downstream of the third alternating current drift tube.

5. The ion implantation system of claim 4, wherein the alternating current voltage component comprises a third alternating current voltage source coupled to deliver a third alternating current voltage signal to the third alternating current drift tube at a third frequency, wherein the third frequency comprises an integer multiple of the first frequency and is different from the second frequency.

6. The ion implantation system of claim 5, wherein the second frequency is twice the first frequency, wherein the third frequency is three times the first frequency.

7. The ion implantation system of claim 5, wherein the first frequency comprises a frequency of at least 13.56 megahertz, and wherein the third frequency comprises a frequency of 120 megahertz or less.

8. The ion implantation system of claim 1, further comprising a dc accelerator column disposed between the ion source and the buncher and arranged to accelerate the continuous ion beam to an energy of at least 200 kev.

9. An ion implantation system, comprising:

an ion source that generates a continuous ion beam;

a beam expander disposed downstream of the ion source to receive the continuous ion beam and output a focused ion beam, wherein the beam expander comprises:

A first grounded drift tube arranged to receive the continuous ion beam;

a first alternating current drift tube disposed adjacent to and downstream of the first grounded drift tube;

a second alternating current drift tube disposed adjacent to and downstream of the intermediate ground drift tube;

a second grounded drift tube, wherein the second grounded drift tube is disposed adjacent to and downstream of the second alternating current drift tube; a kind of electronic device with high-pressure air-conditioning system

An alternating current voltage assembly comprising:

a first alternating current voltage source coupled to deliver a first alternating current voltage signal to the first alternating current drift tube at a first frequency; a kind of electronic device with high-pressure air-conditioning system

A second alternating current voltage source coupled to deliver a second alternating current voltage signal to the second alternating current drift tube at a second frequency, wherein the second frequency comprises an integer multiple of the first frequency,

and

A linear accelerator disposed downstream of the beam shaper to receive and accelerate the beam shaper ion beam.

10. An ion implantation system, comprising:

an ion source that generates a continuous ion beam;

A beam expander disposed downstream of the ion source to receive the continuous ion beam and output a focused ion beam, the beam expander comprising:

a first alternating current drift tube receiving a first alternating current signal at a first frequency; a kind of electronic device with high-pressure air-conditioning system

A second alternating current drift tube disposed downstream of the first alternating current drift tube to receive a second alternating current signal at a second frequency, the second frequency being an integer multiple of the first frequency;

a linear accelerator disposed downstream of the beam shaper to receive and accelerate the beam shaper ion beam;

a first grounded drift tube disposed upstream of the first alternating current drift tube;

an indirectly ground drift tube disposed downstream of the first alternating current drift tube; and

a second grounded drift tube, wherein the second grounded drift tube is disposed adjacent to and downstream of the second alternating current drift tube.