阅读说明：本技术 离子注入系统 (Ion implantation system ) 是由 法兰克·辛克莱 于 2021-02-20 设计创作，主要内容包括：本发明提供一种离子注入系统,包含：离子源；以及聚束器,从离子源接收连续离子束并输出聚束式离子束。聚束器可包含漂移管组件,漂移管组件具有交替顺序的接地漂移管和交流电漂移管。漂移管组件可包含：第一接地漂移管,布置成接收连续离子束；至少两个交流电漂移管,在第一接地漂移管的下游；第二接地漂移管,在至少两个交流电漂移管的下游。离子注入系统可包含交流电电压组件,交流电电压组件耦接到至少两个交流电漂移管且包括分别耦接到至少两个交流电漂移管的至少两个交流电电压源。离子注入系统可包含安置在聚束器下游的线性加速器,线性加速器包括多个加速工作台。(The present invention provides an ion implantation system, comprising: an ion source; and a buncher receiving the continuous ion beam from the ion source and outputting a bunched ion beam. The buncher may comprise a drift tube assembly having an alternating sequence of grounded drift tubes and alternating current drift tubes. The drift tube assembly may comprise: 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; and a second grounded drift tube downstream of the at least two AC 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 respectively coupled to the at least two ac drift tubes. The ion implantation system may include a linear accelerator disposed downstream of the buncher, the linear accelerator including a plurality of acceleration stages.)

1. An ion implantation system, comprising:

an ion source that generates a continuous ion beam;

a buncher disposed downstream of the ion source to receive the continuous ion beam and output a bunched ion beam, wherein the buncher comprises a drift tube assembly comprising an alternating sequence of grounded drift tube sets and alternating current drift tube sets arranged in an alternating manner with respect to each other, the drift tube assembly further 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 AC drift tubes; and

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 buncher to receive and accelerate the bunched ion beam.

2. The ion implantation system of claim 1, wherein the alternating current voltage assembly comprises:

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

a second alternating current voltage source coupled to deliver a second alternating current voltage signal to a second alternating current drift tube 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.

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

4. The ion implantation system of claim 2, wherein the first frequency is 13.56 megahertz and the second frequency is 27.12 megahertz.

5. The ion implantation system of claim 2, the buncher further comprising:

the first grounded drift tube;

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

an intermediate grounded drift tube arranged downstream of the first alternating current drift tube;

the second alternating current drift tube disposed adjacent to and downstream of the intermediate grounded 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.

6. The ion implantation system of claim 5, the buncher further comprising:

the first grounded drift tube;

the first ac drift tube, wherein the first ac drift tube is disposed adjacent to and downstream of the first grounded drift tube;

a first intermediate grounded drift tube arranged 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 intermediate grounded 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 grounded 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.

7. The ion implantation system of claim 6, 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.

8. The ion implantation system of claim 7, wherein the second frequency is twice the first frequency, wherein the third frequency is three times the first frequency.

9. The ion implantation system of claim 7, 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 than 120 megahertz.

10. 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.

11. An ion implantation system, comprising:

an ion source that generates a continuous ion beam;

a buncher disposed downstream of the ion source to receive the continuous ion beam and output a bunched ion beam, wherein the buncher 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;

an intermediate grounded drift tube arranged downstream of the first alternating current 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 AC current drift tube; and

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; and

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 buncher to receive and accelerate the bunched ion beam.

12. An ion implantation system, comprising:

an ion source that generates a continuous ion beam;

a buncher disposed downstream of the ion source to receive the continuous ion beam and output a bunched ion beam, the buncher comprising:

the first alternating current drift tube receives a first alternating current signal at a first frequency; and

a second ac drift tube disposed downstream of the first ac drift tube to receive a second ac electrical signal at a second frequency, the second frequency being an integer multiple of the first frequency; and

a linear accelerator disposed downstream of the buncher to receive and accelerate the bunched ion beam.

13. The ion implantation system of claim 12, further comprising

A first grounded drift tube disposed upstream of the first AC drift tube;

an intermediate grounded drift tube arranged 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 AC current drift tube.

Technical Field

The present disclosure relates generally to ion implantation apparatus, 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 assemblies. The ion source may comprise a chamber for generating ions. The beamline components may include, for example, a mass analyzer, a collimator, 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 filters, focuses, and manipulates an ion beam of a particular material, shape, energy, and/or other qualities. The ion beam passes through a beamline assembly and may be directed toward a substrate mounted on a platen or clamp.

One type of ion implanter suitable for producing medium and high energy ion beams uses a linear accelerator or LINAC in which a series of electrodes arranged around the beam as a conduit accelerate the ion beam to increasingly higher energies along a series of conduits. 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 the ion beam as it passes through the beamline. The initial stage of the LINAC may be referred to as a buncher, where a continuous ion beam is received by the buncher and output as a bunched ion beam in packets. Depending on the frequency and amplitude of the AC voltage signal, the acceptance or phase capture of an ion beam conducted through a known "double gap" buncher using powered electrodes may be about 30-35%, which means that 65% more of the beam current is lost when conducting to the accelerating 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 an alternating sequence of sets of grounded drift tubes and sets of AC drift tubes arranged in an alternating manner with respect to 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 include: a first AC voltage source coupled to deliver a first AC voltage signal at a first frequency to a first AC drift tube of the at least two AC drift tubes; and a second AC voltage source coupled to deliver a second AC voltage signal at a second frequency to a second AC drift tube of the at least two AC drift tubes. 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 buncher disposed downstream of the ion source to receive the continuous ion beam and output a bunched ion beam. The buncher may include a drift tube assembly characterized by an alternating sequence of sets of grounded drift tubes and AC drift tubes arranged in an alternating manner with respect to each other. The drift tube assembly may comprise: 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 respectively coupled to the at least two AC drift tubes. The ion implantation system may further include a linear accelerator disposed downstream of the buncher, 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 comprise: 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 intermediate grounded drift tube disposed downstream of the first AC drift tube; and a second AC drift tube disposed adjacent to and downstream of the intermediate grounded drift tube. The multi-ring drift tube assembly can 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 also include an AC voltage component electrically coupled to the multi-ring drift tube component. The AC voltage component may include: 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 to scale. The drawings are merely representational views and are not intended to portray specific parameters of the disclosure. The drawings are intended to depict example 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 buncher in accordance with an embodiment of the present disclosure.

Fig. 3 illustrates another exemplary buncher according to other embodiments of the present disclosure.

Fig. 4 depicts modeled results of the 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 beamers, 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 according to other embodiments of the present disclosure.

Fig. 8 illustrates another exemplary buncher according to other embodiments of the present disclosure.

Fig. 9 illustrates yet another exemplary buncher according to 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;

109A 1: a back end;

109A 2: a front end;

109B: packaging;

110: an analyzer;

111: an upstream beam line;

114. 212, and (3): a linear accelerator;

115: a high energy ion beam;

116: a filtering 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: an acceleration table;

164: a controller;

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

206: an intermediate grounded drift tube;

234: a first grounded drift tube;

236: a first AC drift tube;

238: a first intermediate grounded drift tube;

240: a second AC drift tube;

242: a second intermediate grounded drift tube;

244: a third AC drift tube;

246: a second grounded drift tube;

600: a process flow;

602. 604, 606, 608: framing;

l: a length;

V₁cos(ωt+φ₁)、V₂cos(2ωt+φ₂)、V₃cos(3ωt+φ₃) AC: a voltage signal.

Detailed Description

Apparatus, 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. Rather, 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 potentially also including a plurality of 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 improved high energy ion implantation systems based on beamline architectures are provided herein. For simplicity, the ion implantation system may also be referred to herein as an "ion implanter". Various embodiments provide novel configurations for providing the ability to generate high energy ions, wherein the final ion energy delivered to the substrate may be 300 kilo-electron volts, 500 kilo-electron volts, 1 mega-electron volts, or greater. In exemplary embodiments, the novel buncher design may 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 an implantation system 100 is depicted in block form. The ion implantation system 100 may represent a beamline ion implanter where some elements are omitted for clarity of illustration. The ion implantation system 100 may comprise an ion source 102 and a gas box 107 maintained at high voltages 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 kev to 100 kev, but 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 include an analyzer 110 to analyze the received ion beam. Accordingly, in some embodiments, the analyzer 110 may receive the ion beam 106 having an energy applied by extraction optics located at the ion source 102, wherein the ion energy is in a range of 100 or less than 100 kev, and specifically 80 or less than 80 kev. In other embodiments, the analyzer 110 may receive an ion beam that is accelerated by the 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 also include a buncher 130 and a linear accelerator 114 (shown in phantom) disposed downstream of the buncher 130. The operation of the buncher 130 is detailed below. Briefly, the buncher 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 a beam as a bunched ion beam. In the bunched ion beam, the ion beam is output in discrete packets. Meanwhile, the energy of the ion beam may be increased by the buncher 130. The linear accelerator 114 may include a plurality of accelerator stages 126 arranged in series, as shown. The accelerator stages 126 may operate similar to a buncher to output a bunched ion beam at a given stage and accelerate the ion beam to a higher energy in each stage. Thus, the buncher may be considered a first accelerator stage, which differs from the downstream accelerator stage in that it receives the 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, a high energy ion beam, represented by the high energy ion beam 115, may be delivered to the end station 122 to process the substrate 124.

In some embodiments, where the ion beam 106 is provided directly to the analyzer 110, the buncher 130 may receive the ion beam 106 as a continuous ion beam at a relatively low energy (e.g., less than 100 kev), as mentioned. In other embodiments, where the ion implantation system includes a DC accelerator column, the ion beam 106 may be accelerated to be fed as a continuous ion beam at energies of at most 500 kev or greater than 500 kev. In these different cases, the exact Alternating Current (AC) voltage applied by the buncher 130 may be adjusted according to the ion energy of the continuous ion beam received by the buncher 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 for medium energy ion implanters. The DC accelerator column may accelerate the ion beam 106, with the accelerated ion beam 109 received by the analyzer 110 and the buncher 130 at an energy 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 an exemplary beamformer structure, shown as beamformer 130, of a linear accelerator according to an embodiment of the present disclosure. The buncher 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 the accelerated ion beam 109. As shown, the first grounded drift tube 152 is connected to 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 an AC voltage signal, typically in the radio frequency range (RF range), which is used to accelerate and manipulate the accelerated ion beam 109. In the embodiment of fig. 2, the AC drift tube assembly 156 contains only one AC drift tube. In other embodiments, the AC drift tube assembly 156 may comprise 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, a conductive ion beam passes through the hollow cylinder, and some portions of the ion beam are accelerated and others are decelerated in a manner that bunches the ion beam into discrete packets (shown as bunches 109A) to be received and further accelerated by an acceleration stage 158 located downstream. The drift tube assembly 150 may be constructed of graphite or a similar suitable material configured to minimize contamination of an ion beam conducted therethrough. Subsequent acceleration stages, indicated by acceleration stage 158, may operate at a well-defined frequency ω, and capturing the beaming into this acceleration structure may be limited to a phase angle of approximately ± 5 ° with respect to this fundamental angular frequency ω. To transmit the largest possible current through the entire beamline, the beamformer 130 needs to be arranged to generate one beamform for each period of this fundamental frequency ω.

As shown in fig. 2, the buncher 130 also includes an AC voltage component 140, the AC voltage component 140 arranged to send an AC voltage signal to the AC drift tube assembly 156 to drive a varying voltage at the powered drift tube of the AC drift tube assembly 156. The varying voltage on the AC drift tube assembly 156 provides different acceleration of the ions depending on their arrival time at the AC drift tube assembly 156. In this manner, the rear end 109A1 of the bunch 109A gives a greater velocity than the front end 109A2 of the bunch 109A, and upon reaching the acceleration stage 158, the entire bunch 109A becomes as compact as possible. In various embodiments, the AC voltage signal may be a composite of multiple individual AC voltage signals that are superimposed to generate the AC voltage signal in a manner that provides 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, wherein 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 a harmonic of the first frequency, wherein the frequency may be twice, three times, etc. the first frequency.

In the embodiment of fig. 2, AC voltage assembly 140 is shown to generate three different AC voltage signals, denoted V₁cos(ωt+φ₁)、V₂cos(2ωt+φ₂) And V₃cos(3ωt+φ₃). For purposes of illustration, the AC voltage signal is shown as a sinusoidal signal, but other waveform shapes are possible. The AC voltage assembly 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, respectivelyThree AC voltage signals. The AC voltage supply may be implemented using an RF amplifier driven by a synchronization signal generator. The generic term V refers to the maximum amplitude of the AC voltage signal, and 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 parts and three times, respectively, the frequency of the first signal ω. As shown in fig. 2, the AC voltage component 140 may include an adder 148, wherein 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 AC voltage signal has a maximum frequency of approximately 120 megahertz or less than 120 megahertz.

The composite AC voltage signal 149 is designed to adjust the phase dependence of the 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 bunching to a downstream acceleration stage, some portion of the ion beam is lost to walls or other surfaces due to the nature of the acceleration and bunching processes. Receive 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 apparatuses employing a linear accelerator, the acceptance may be about 30% to 35% at maximum when various conditions are optimized. Such known ion implantation systems may drive the buncher with AC voltage signals having frequencies of 10 mhz, 13.56 mhz, or 20 mhz, and voltage amplitudes in the tens of kilovolts range. It is noted that the AC voltage signal in known ion implantation systems may be generated as a simple AC voltage signal of a single frequency.

It is noted that the fundamental component of the composite AC voltage signal can be reduced to V₁cos (ω t), in which the relative phase with respect to the other two AC voltage signals is shifted by a respective phase₂Or phi₃It is given. As described in detail below, these offsets may be adjusted to increase reception.

In particular, the present inventors have found that applying multiple frequencies to produce a composite (composite waveform) produces better output phase coherence/acquisition than known bunchers that employ AC voltage signals at a single frequency.

Turning to fig. 3, a structure of an exemplary buncher (buncher 160) of a linear accelerator according to other embodiments of the present disclosure is shown. The buncher 160 may include a drift tube assembly 170, the drift tube assembly 170 including a first grounded drift tube 182 arranged to receive a continuous ion beam, shown as the accelerated ion beam 109. As shown, the first grounded drift tube 182 is connected to electrical ground. The drift tube assembly 170 may further comprise 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 an AC voltage signal, typically in the radio frequency range (RF range), which is used to accelerate and manipulate the accelerated ion beam 109. In the embodiment of fig. 3, AC drift tube assembly 180 contains 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, a conductive ion beam passes through the hollow cylinder, and the ion beam is accelerated in a manner that bunches the ion beam into discrete packets (shown as bunches 109A) to be received and further accelerated by an acceleration stage 192 located downstream. Thus, the drift tube assembly 170 can constitute a multi-ring drift tube assembly having a length (in the direction of propagation of the ion beam) of at least 100 mm and less than 400 mm.

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 assembly 162 may be configured wherein the first AC voltage supply 142 drives an AC drift tube 184, the second AC voltage supply 144 drives an AC drift tube 186, and the third AC voltage supply 146 drives an 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 showsConfiguration to supply the lowest frequency AC voltage signal to the furthest upstream AC drift tube, but in other embodiments the lowest frequency AC voltage signal (V) may be supplied₁cos(ωt+φ₁) Applied to different AC drift tubes. The above applies to intermediate frequency AC voltage signals (V)₂cos(2ωt+φ₂) And a high frequency AC voltage signal (V)₃cos(3ωt+φ₃)). This configuration has an advantage over the configuration in fig. 2 in that the power supply risk of interfering with other power supplies is avoided.

Although it is possible to use multiple frequency AC voltage signals to drive the buncher, 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 beamline, as described in detail below. Thus, such a configuration in a beamline ion implanter has not been contemplated to date. Notably, the inventors have identified configurations that can overcome these considerations by adjusting the drive signals to significantly improve ion beam throughput, particularly for ions having masses in the range of common dopants (e.g., boron, phosphorous, and the like). In particular, in the "single loop" (where "loop" refers to AC drift tube) buncher of fig. 2 or the "three loop" buncher of fig. 3, a composite AC voltage signal is generated in which bunching 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 illustration is shown, including a plot of the drift tube assembly 150 and a corresponding phase diagram (showing distance functions in millimeters along the beam path). The phase diagram is a graph showing 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 mm and 75 mm. At this location, the voltage applied to the AC drift tube assembly 156 (shown by the left ordinate) reaches a maximum of approximately 18 kilovolts and is applied at a frequency of 40 megahertz. 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 20 amu. As shown, the voltage reaches a maximum at the location of the AC drift tube assembly 156, and elsewhereIs zero. At the point of entry into the AC drift tube assembly 156, the 21 exemplary rays are equally spaced in phase at 18 degree intervals. When passing V-V as generated by AC voltage assembly 140₁cos(ωt+φ₁)+V₂cos(2ωt+φ₂)+V₃cos(3ωt+φ₃) Given the complex AC voltage signal processing, the individual rays converge to the right in phase as shown.

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

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

Fig. 5A and 5B are graphs showing the phase behavior of different rays of an ion beam, highlighting the benefit of applying a composite AC voltage signal according to embodiments of the present invention. Fig. 5A continues with the composite AC voltage parameter of the embodiment of fig. 4, while fig. 5B shows an example of applying a simple AC voltage signal to an ion beam. In the illustration of fig. 5B, the AC signal is derived by: v is V_maxcos (ω t + φ), while in FIG. 5A, the AC signal is given by: v is V₁cos(ωt+φ₁)+V₂cos(2ωt+φ₂)+V₃cos(3ωt+φ₃). In both cases, the frequency ω is 40 mhz.

In two different graphs, the phase behavior depicts the phase of a given ray at a specified distance from a point proximate to 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 at which the phases of the different rays of the ion beam can conveniently converge. Thus, referring again to fig. 4, in the bunching 109A, operation of the AC drift tube assembly 156 tends to accelerate the phase lag ions (back end 109A1) and tends to decelerate the phase lead ions (front end 109A2), causing phase convergence as at 700 millimeters.

In fig. 5B, most phase coherence conditions yield a maximum relative reception of 35%, and even with an initial phase difference of only 30 degrees, there is still a small degree of phase difference at 400 millimeters. As shown, for other voltages, the behavior is worse. Notably, the embodiment of fig. 5A produces convergence at 700 millimeters, slightly longer than the single frequency beamformer results that 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 kilovolts. In the case of a single frequency beamformer, operation at 20 kv AC voltage amplitude results in convergence at 400 mm. Although the embodiment of fig. 5A may entail a slightly longer spacing between the beamformer and the accelerator (700 mm versus 400 mm) as compared to a single frequency beamformer architecture, the benefit is substantially greater reception and thus beam current conduction into the main accelerator stage of the LINAC. In various additional embodiments, the convergence length may range from 300 millimeters to 1000 millimeters.

Without being limited to a particular theory, the above results can be explained in the following manner. Applying multiple frequencies to generate a composite or composite AC voltage signal (waveform) may produce a waveform having a shape more conducive to incremental capture. In principle, a wave form with sharp features, such as a vertical saw tooth shape, as shown in fig. 10. This waveform can accelerate the ions in a manner such that the ions come together in a "saw tooth" to form a bunch, theoretically achieving about 100% trapping. It is worth noting that in practical beamformers, a resonator based on a resonant circuit is used to drive an AC voltage waveform of the relevant frequency (in the megahertz range), where the resonant circuit itself produces a sinusoidal wave that does not produce as high a capture as the vertical saw tooth case. In the present method, the addition of a plurality of sinusoidal waveforms of different frequencies is used to generate a composite waveform that can exhibit a shape that is closer to an ideal sawtooth shape, and thus increases improved output phase coherence and capture, 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 assembly is at an integer multiple of the fundamental frequency, each ion bunch will experience the same field, and the fundamental harmonic highest common factor frequency remains unchanged at the fundamental frequency.

While in principle adding a large number of waveforms, such as Fourier series, may produce a composite waveform that more accurately approximates a sawtooth waveform, such an approach may be impractical due to the increased cost of adding this 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 work similarly to applying different sinusoidal waveforms to a single electrode, and found that applying only two waveforms produces a significant improvement in output phase coherence and capture, similar to the case of three waveforms, as opposed to the relatively low output phase coherence produced by a single frequency waveform.

Although the additional stages of the LINAC may accelerate and further bunch ion packets in a similar manner to the buncher of embodiments 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 buncher has already converged a substantial portion of the various rays of the bunched ion beam to the entrance of the accelerator stage, there may be less need to further improve the phase convergence. This fact allows a simpler design of the AC voltage assembly driving the accelerator stage 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 generating a composite AC voltage signal based on three AC voltage signals and employing a multi-ring drift tube assembly including 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, multi-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 in accordance with 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 keV. 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 an ion energy of 200 to 500 kev or more.

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

At block 606, a 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 directed through a third AC drift tube of the multi-ring drift tube assembly while applying a third AC voltage signal 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 can be output from the multi-ring drift tube assembly as a bunched ion beam.

Fig. 7 illustrates another exemplary buncher (buncher 200) for a linear accelerator, according to other embodiments of the present disclosure. The buncher 200 may comprise a drift tube assembly 201, said drift tube assembly 201 comprising a first grounded drift tube 202 arranged to receive a continuous ion beam, shown as accelerated ion beam 109. As shown, the first grounded drift tube 202 is connected to electrical ground. Drift tube assembly 201 may further comprise an AC drift tube assembly 203 disposed downstream of first grounded drift tube 182. Similar to the aforementioned AC drift tube assemblies, the AC drift tube assembly 203 is arranged to receive an AC voltage signal, typically in the radio frequency range (RF range), which is used to accelerate/decelerate and manipulate the accelerated ion beam 109. In the embodiment of fig. 7, 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 bunches the ion beam into discrete packets (shown as packets 109B), a conductive ion beam passes through the hollow cylinder and accelerates/decelerates the ion beam to be received and further accelerated by a linear accelerator 212 disposed downstream. Thus, drift tube assembly 201 can constitute a multi-ring drift tube assembly having a length (in the direction of propagation of the ion beam) of at least 100 mm and less than 400 mm.

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 wherein a first AC voltage supply 214 drives the AC drift tube 204 and a second AC voltage supply 216 drives the AC drift tube 208. In this configuration and the configuration of fig. 8, the two different AC voltage supplies may output a first frequency of 40 mhz and a second frequency of 80 mhz, or alternatively the two different AC voltage supplies may output a first frequency of 13.56 mhz and a second frequency of 27.12 mhz, according to different non-limiting embodiments.

These AC voltage signals may be synchronized in time by the controller 164 to produce a beam behavior similar to that of a single drift tube by a composite signal given by: v is V₁cos(ωt+φ₁)+V₂cos(2ωt+φ₂). In this way, the output phase coherence as a function of the input phase of the ions may be improved over single frequency bunchers 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) may be supplied₁cos(ωt+φ₁) Applied to different AC drift tubes.

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

The embodiment of fig. 8 shows a drift tube assembly 221 characterized by an alternating sequence of one AC drift tube and one grounded drift tube as the ion beam passes down the beam line. In other embodiments of the alternating sequence, three or more AC drift tubes may be provided in addition to the grounded drift tube disposed between each successive pair of AC drift tubes 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 resonators can be reduced.

It should be noted that in embodiments using two frequencies of up to 200 degrees output phase coherence, up to 55% ion beam acceptance 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 travelling at 180 °, orWhere v is the velocity. This distance produces the maximum acceleration for a given voltage, but may produce some undesirable phase effects. Using as low as 0.2D₀Will 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 depending on ion species, voltage considerations, and other influences according to various embodiments.

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

Fig. 9 provides an example of such an arrangement, in which a buncher 230 is shown. The drift tube assembly 232 includes: a first grounded drift tube 234; a first AC drift tube 236 disposed adjacent to the first grounded drift tube 234 and downstream of the first grounded drift tube 234; a first intermediate grounded drift tube 238 disposed downstream of the first AC drift tube 236; a second AC drift tube 240 disposed adjacent to the first intermediate ground drift tube 238 and downstream of the first intermediate ground drift tube 238; a second intermediate grounded 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 grounded drift tube 242 and downstream of the second intermediate grounded 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. Likewise, providing the first and second intermediate ground drift tubes 238, 242 may prevent cross talk between the first, second, and third AC voltage supplies 142, 144, 146.

In summary, embodiments of the present invention provide beamers that are controlled using multi-frequency signals applied either together to separate AC drift tubes or separately 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 united states FCC, where in an embodiment of the invention each frequency will be an integer multiple of the fundamental frequency applied to the signal. Thus, in a double frequency embodiment, a combination of 13.56 megahertz and 27.12 megahertz is suitable, in a triple 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. The first advantage is achieved by providing a composite AC voltage signal to drive the buncher such that substantially greater ion beam current may be transmitted through the LINAC positioned downstream. Another advantage is the ability to drive a given AC signal from a given power supply of a plurality of AC power supplies to a dedicated electrode, avoiding interference between power supplies that may occur when coupled to a common multiple power supply through a common electrode to drive multiple AC voltage signals, but still driving a larger ion beam current in the case of a composite AC voltage signal.

While certain embodiments of the disclosure have been described herein, the disclosure is not limited thereto, as it is as broad in scope as the art will allow and the specification will be read likewise. The above description is, therefore, not to be taken in a limiting sense. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.