Ion implantation system and linear accelerator having novel accelerator stage configuration

Abstract

To achieve proper acceleration and focusing of an ion beam using a drift tube assembly where no quadrupole element is present.SOLUTION: An ion implantation system includes an ion source and an extraction system which are arranged to generate an ion beam at a first energy, and a linear accelerator which is disposed downstream of the ion source. The linear accelerator arranged to receive the ion beam as a bunched ion beam accelerates the ion beam to a second energy, greater than the first energy. The linear accelerator may include a plurality of acceleration stages. A given acceleration stage of the plurality of acceleration stages includes: a drift tube assembly which is arranged to conduct the ion beam; a resonator which is electrically coupled to the drift tube assembly; and an RF power assembly which is coupled to the resonator and arranged to output an RF signal to the resonator. Consequently, the given acceleration stage does not include a quadrupole element.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present disclosure relates generally to ion implanters, and more particularly to high energy beamline ion implanters. [Background technology]

[0002] 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 include a chamber in which ions are generated. The ion source may further include a power supply and extraction electrode assembly disposed near the chamber. The beamline components may include, for example, a mass analyzer, a first acceleration or deceleration stage, a collimator, and a second acceleration or deceleration stage.

[0003] Implanters capable of producing ion energies of about 1 MeV or greater are often referred to as high energy ion implanters or high energy ion implantation systems. One type of high energy ion implanter employs what is called a linear accelerator or LINAC, where a series of electrodes conduct and accelerate an ion beam to increasingly higher energies along a series of "acceleration stages". RF-LINACs (unless otherwise specified, the term LINAC as used herein refers to RF-LINACs) use electrodes that receive AC voltage signals at high frequencies in the range of tens of megahertz that accelerate the ion beam as it is conducted through a given acceleration stage. Known (RF)LINACs are driven by RF voltages of 13.56 MHz to 120 MHz that are applied to the various acceleration stages of the LINAC. The number of acceleration stages can range up to 12 stages.

[0004] Known ion implantation systems employ RF-LINACs, where each acceleration stage includes a resonator coupled to an acceleration electrode to drive an RF signal at a predetermined voltage amplitude to achieve a target acceleration of the energy of the ion beam. In this manner, the ion energy of the ion beam passing through the LINAC is increased stepwise at each acceleration stage until the final target energy is reached. A given acceleration stage includes an acceleration electrode and a ground electrode arranged as a hollow conductive "drift tube" separated by a gap between the drift tubes across which the acceleration of the ion beam occurs.

[0005] To avoid unwanted beam spread, high energy ion implanters using RF-LINACs employ DC quadrupole components as an integral part of each acceleration stage of the LINAC. These quadrupole components may be configured as electrostatic or magnetic quadrupoles.

[0006] These quadrupole components used in LINACs for high energy injection systems take advantage of accelerator designs used in high energy physics research. The use of quadrupoles addresses a problem addressed in part by Earnshaw's theorem, which states that electrostatic interactions of charges alone cannot maintain a collection of point charges in a stable, steady-state equilibrium configuration. Quadrupoles advantageously reduce the tendency of the RF electrodes of the acceleration stage to cause radial defocusing as a result of phasing of the ion beam as it is conducted through the acceleration stage.

[0007] In known designs, the quadrupole components may be conveniently arranged around the grounded drift tube of a given acceleration stage. In some designs, two separate quadrupoles may be arranged along either end of the acceleration stage, while other designs may use one quadrupole per stage. However, the acceleration stage designs of known ion implanter RF-LINACs are relatively complex.

[0008] In view of the above, it would be useful to further improve the current configuration of the RF-LINAC of an ion implanter.

[0009] It is with respect to these and other considerations that this disclosure is offered. Summary of the Invention

[0010] Various embodiments relate to a novel ion implanter.

[0011] In one embodiment, an ion implantation system includes an ion source and extraction system configured to generate an ion beam at a first energy, and a linear accelerator disposed downstream of the ion source, the linear accelerator configured to receive the ion beam as a bunched ion beam and accelerate the ion beam to a second energy greater than the first energy, the linear accelerator including a plurality of acceleration stages. Thus, a given acceleration stage of the plurality of acceleration stages may include a drift tube assembly configured to conduct the ion beam, a resonator electrically coupled to the drift tube assembly, and an RF power assembly coupled to the resonator and configured to output an RF signal to the resonator, the given acceleration stage not including a quadrupole element.

[0012] In another embodiment, a method of operating an ion implanter may include generating an ion beam, bunching the ion beam, where the ion beam is converted into a plurality of bunched ion packets, and accelerating the bunched ion packets to a high ion energy through a plurality of acceleration stages of a linear accelerator. Thus, accelerating may include applying an RF signal to a drift tube assembly to accelerate the ion beam from an initial ion energy to a higher ion energy in at least one of the plurality of acceleration stages without applying a quadrupole field to the ion beam, where the ion beam is focused by the drift tube assembly, and implanting the ion beam at the ion energy into a substrate.

[0013] In a further embodiment, a linear accelerator is provided in an ion implantation system. The linear accelerator may include a plurality of acceleration stages, at least one of which includes a drift tube assembly configured to transmit an ion beam as a bunched ion beam. The drift tube assembly may include a triple gap configuration or a double gap configuration. The at least one acceleration stage may further include a resonator electrically coupled to the drift tube assembly. In this manner, the at least one acceleration stage of the linear accelerator does not include a quadrupole element. [Brief description of the drawings]

[0014] [Figure 1A] 1 illustrates an exemplary apparatus according to an embodiment of the present disclosure. [Figure 1B] The reference device is shown. [Figure 1C] 1 illustrates an exemplary ion implantation system according to an embodiment of the present disclosure. [Figure 1D] 1 illustrates an exemplary apparatus according to an embodiment of the present disclosure. [Figure 2A-2C] 1 illustrates a simulation of the electrical behavior of an exemplary linear accelerator during operation, according to an embodiment of the present disclosure. [Diagram 3] 1 illustrates a focusing mechanism in an exemplary acceleration stage of a linear accelerator. [Figure 4] 1 illustrates an exemplary process flow.

[0015] The drawings are not necessarily to scale. The drawings are merely representational and are not intended to represent specific parameters of the present disclosure. The drawings are intended to illustrate exemplary embodiments of the present disclosure and therefore should not be considered limiting in scope. In the drawings, like numbers represent like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 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. 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.

[0017] Terms such as "top," "bottom," "upper," "lower," "vertical," "horizontal," "lateral," and "longitudinal" may be used herein to describe the relative placement and orientation of these components and their constituent parts with respect to the geometry and orientation of the components of a semiconductor manufacturing device as seen in the drawings. The terms may include the specifically mentioned words, derivatives thereof, and words of similar import.

[0018] As used herein, elements or operations described in the singular following the words "a" or "an" are understood to potentially include 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.

[0019] Provided herein are approaches for improved beamline architecture-based high energy ion implantation systems and components, specifically linear accelerator-based ion implanters. For simplicity, the ion implantation system may also be referred to herein as an "ion implanter." Various embodiments involve novel approaches that provide the ability to flexibly adjust the effective drift length within the acceleration stage of the linear accelerator.

[0020] FIG 1A illustrates a schematic diagram of a linear accelerator according to an embodiment of the present disclosure. The linear accelerator 10 includes an acceleration stage 20-A and associated electrical circuitry including an RF power assembly 40-A, and a resonator 22. As shown in FIG 1A, the linear accelerator 10 may include multiple acceleration stages, shown as acceleration stages 20-B...20-N. In various embodiments, one or more of the stages of the linear accelerator 10 may include components of acceleration stage 20-A, as described in detail herein.

[0021] To illustrate the operation of the linear accelerator 10, FIG. 1C illustrates an ion implanter 100. This implanter may represent a beamline ion implanter, but for clarity of illustration, some elements are not shown. The ion implanter 100 may include an ion source 102 and a gas box 107 disposed within a terminal 104, as known in the art. The ion source 102 may include an extraction system including extraction components and filters (not shown) to generate an ion beam 106 at a first energy. A suitable ion energy range for the first ion energy is, for example, 5 keV to 100 keV, although embodiments are not limited thereto. To form a high-energy ion beam, the ion implanter 100 includes various additional components for accelerating the ion beam 106.

[0022] As shown, the ion implanter 100 may include an analyzer 110 operable to analyze the ion beam 106 in a manner similar to known devices by varying the trajectory of the ion beam 106. The ion implanter 100 may further include a buncher 112 and a linear accelerator 10 (shown in dashed lines) disposed downstream of the buncher 112, where the linear accelerator 10 is configured to accelerate the ion beam 106 to form a high energy ion beam 115 having an ion energy greater than that of the ion beam 106 before entering the linear accelerator 10. It should be noted that in different configurations, the buncher 112 may be considered part of the linear accelerator or a separate element from the linear accelerator. As is known, a buncher, such as the buncher 112, operates to receive an ion beam as a continuous ion beam and output the ion beam as a bunched ion beam (i.e., a plurality or series of discrete ion packets separated in space and time). Similar to an acceleration stage, the buncher may apply a radio frequency signal to the ion beam, resulting in the bunching of the initially continuous ion beam. Unless otherwise specified, the "acceleration stage" of the linear accelerator described herein processes and accelerates an already bundled ion beam.

[0023] As also discussed with respect to FIG. 1A, the linear accelerator 10 may include multiple acceleration stages (20-A through 20-N) arranged in series as shown. In various embodiments, the ion energy of the high-energy ion beam 115 may represent the final ion energy of the ion beam 106, or approximately the final ion energy of the ion beam 106. In various embodiments, the ion implanter 100 may include additional components such as a filter magnet 116, a scanner 118, and a collimator 120. The general functions of the scanner 118 and collimator 120 are well known and will not be described in further detail herein. In this manner, the high-energy ion beam represented by the high-energy ion beam 115 may be delivered to a final station 122 for processing a substrate 124. A non-limiting energy range of the high-energy ion beam 115 includes 500 keV-10 MeV, and the ion energy of the ion beam 106 is increased stepwise through the various acceleration stages of the linear accelerator 10.

[0024] Returning to FIG. 1A, two acceleration stages are shown in detail, with acceleration stage 20-A and acceleration stage 20-B configured as triple gap electrode assemblies. As used herein, the term "triple gap" may mean that there are three gaps between the electrodes in a given acceleration stage. For example, in acceleration stage 20-A and acceleration stage 20-B, the electrode assembly includes a first grounded drift tube 34, an AC drift tube assembly (including a first AC drift tube electrode 30 and a second AC drift tube electrode 32), and a second grounded drift tube 36. This assembly of electrodes is all configured as a hollow conductive cylinder through which the ion beam 106 is conducted. According to various embodiments of the present disclosure, the ion beam 106 may be received at a given acceleration stage as a bunched ion beam, meaning that the ion beam 106 is received as multiple packets separated from each other. Thus, different ion packets of the ion beam 106 arrive at the acceleration stage 20-A at different times, are accelerated accordingly, and are conducted through the acceleration stage 20-A in turn.

[0025] As shown in FIG. 1A, RF power assembly 40-A is electrically coupled to resonator 22 and drives an RF voltage signal within resonator 22. For example, resonator 22 can be configured as a high frequency step-up transformer and output an RF voltage signal having a high voltage amplitude, such as 10 kV to 100 kV or other high voltage. Similar resonators may be included in other acceleration stages of linear accelerator 10 and, in some embodiments, may be individually coupled to dedicated RF power assemblies. Here, RF power assembly 40-B is shown for acceleration stage 20-B. Resonator 22 has a first output end coupled to first AC drift tube electrode 30 and a second output end coupled to second AC drift tube electrode 32. Transmitting an RF signal to resonator 22 may cause resonator 22 to resonate depending on the frequency of the RF voltage and the configuration of resonator 22. More specifically, the resonator 22 exhibits a fundamental (resonant) frequency corresponding to a first Eigenmode frequency and outputs a voltage signal to the first AC drift tube electrode 30 that is shifted approximately 180 degrees from the voltage signal output to the second AC drift tube electrode 32. In this manner, the ion beam 106 is accelerated across the gap between the various electrodes of the acceleration stage 20-A.

[0026] 1B, a reference linear accelerator 50 is shown which, like linear accelerator 50, may have multiple acceleration stages. These acceleration stages are represented by two acceleration stages, acceleration stage 60-A and acceleration stage 60-B. Acceleration stage 60-A is shown in some detail and is configured as a triple gap electrode assembly as described above with respect to FIG. 1A. The difference with acceleration stage 20-A is that first grounded drift tube 54 and second grounded drift tube 56 may be longer than the corresponding grounded drift tubes in acceleration stage 20-A.

[0027] The reference linear accelerator 50 illustrates some components of known linear accelerators for ion implanters. As is known, ion implanters process ion species based on elements or molecules such as hydrogen, helium, oxygen, boron, carbon, phosphorus, arsenic, to name a few species.

[0028] In order to properly accelerate and conduct the ion beam 106, the reference linear accelerator 50 includes, in addition to the resonator 22, a quadrupole element 62 and a quadrupole element 64. These quadrupole elements may be electrostatic or magnetic quadrupoles. The quadrupole elements 62 and 64 act to focus the ion beam 166, thus preventing excessive loss of current and energy as the ion beam accelerates through the acceleration stage 60-A. The acceleration stage 60-B and other acceleration stages of the reference linear accelerator 50 also include similar quadrupole elements. Focusing is necessary to maintain good transmission of the beam, because the mutual repulsion of the positive ions in the bunch will exert forces ("space charge forces") that, if left unchecked, will cause the beam to spread laterally and vertically, eventually causing the ions to collide with the side walls or to move out of phase relationship suitable for acceleration.

[0029] Although the general configuration of the acceleration stage shown in Figure 1B is commonly used in linear accelerator based ion implanters, the inventors have found that proper acceleration and focusing of the ion beam can be achieved using a drift tube assembly without the presence of quadrupole elements, as generally shown in acceleration stage 20-A in Figure 1A. It is commonly accepted that a focusing structure such as a quadrupole element is required for a given acceleration stage, because radial defocusing occurs as a result of phase focusing in RF acceleration structures such as AC drift tubes in linear accelerators. However, modeling by the inventors has shown that proper focusing can still be achieved in RF linear accelerators without the presence of quadrupole elements.

[0030] In Figures 2A to 2C, a simulation of the electrical behavior during operation of an exemplary linear accelerator according to an embodiment of the present disclosure is shown. In particular, these figures represent an ion trajectory tracking program with doubly charged phosphate ions, output as a result of various calculations performed. The ions are modeled to enter the left side of the figure with an initial energy of 540 keV and accelerated in a triple gap accelerator (the position of the accelerating electrodes is shown in the center of the X-axis) with a maximum voltage amplitude of 80 kV, and as the ions accelerate, they reach an energy of 900 keV. Figure 2A shows the magnitude of the potential on the electrodes (left axis) and the energy of the ions (right axis). Figure 2B shows the X and Y positions of the ions relative to the axis, while Figure 2C shows the phase of the RF voltage at the position of the ions in the simulation. The results show that the doubly charged phosphate ions are on average focused towards the center of the beamline, but Figure 2C in particular shows that the phase of the ions is more convergent at the exit than at the entrance. Note that for simplicity, space charge forces are not included in these simulations, and in actual practice the ion beam does not focus to a point in x, y, or φ. However, by carefully adjusting the phase of the voltages, the focusing forces are balanced against the space charge forces, and small parallel beam inputs and outputs are achieved at each acceleration stage, allowing good beam transmission along the beamline.

[0031] While the above-described embodiments have focused on an acceleration stage having a triple gap configuration, in further embodiments, a double gap acceleration stage without quadrupole elements is provided. Referring to FIG. 1D, a linear accelerator 70 is shown with details of two acceleration stages. Acceleration stage 80-A and acceleration stage 80-B are configured as double gap electrode assemblies. The term "double gap" as used herein may mean that there are two gaps between the electrodes in a given acceleration stage. For example, in acceleration stage 80-A and acceleration stage 80-B, the electrode assembly includes a first grounded drift tube 74, only one AC drift tube electrode 72, and a second grounded drift tube 76. Similar to the acceleration stage with a triple gap configuration, one or more acceleration stages of the linear accelerator 70 may be configured without quadrupole elements and still be able to accelerate and focus an ion beam.

[0032] In view of the above results, a linear accelerator for an ion implanter that does not use quadrupoles between each acceleration stage in the accelerator can effectively accelerate and focus an ion beam. Although the above results are described for phosphorus, these results can be readily applied to a wide range of mass / charge ratios, including ions commonly used in ion implanters.

[0033] Without being limited to a particular theory, the ability to achieve adequate focusing of ions conducted through an RF LINAC acceleration electrode assembly without the use of quadrupole elements can be derived from the fact that the particles used in ion implanters are relatively heavy and accelerated to only a few MeV. Because of this, the relatively high mass and relatively low energy ions typically used in ion implanters can only achieve a fraction of the speed of light (e.g., less than 0.1c). The general adoption of quadrupoles in ion implanter LINACs is predicted based on previously developed linear accelerator technology employed in accelerators used for high energy physics research. These systems mostly deal with particles (protons and electrons) that travel at velocities very close to the speed of light. At these high energies, all particles travel at speeds that are essentially faster than the speed of light. TIFF2024170437000002.tif12170, the time spent on any given length of the beamline is equal. This results in no net focusing or defocusing occurring in the acceleration gap, and the quadrupole is required to counteract the ever-present space charge forces. The situation is different for the slower ion beams used in semiconductor manufacturing, as can be seen with reference to FIG. 3, which shows a detail of a single acceleration gap in the acceleration stage 300. As shown there, a power supply 302 generates a voltage difference between a pair of cylindrical electrodes (304, 306), shown in cross section. Here, the shape of the equipotential curves 308 of the accelerating electric field is shown, and how the equipotential curves 308 expand towards the inside of the tubular electrodes (first electrode 404 and second electrode 306). This expansion is determined by the Laplace equation TIFF2024170437000003.tif10170, which gives the geometry of the equipotential established by a set of conductors in a vacuum. As shown, the expansion of the front half of the gap exerts a force on the off-axis ion beam 310 particles toward the axis (focusing force), and the symmetric expansion of the back half of the gap exerts a force away from the axis (defocusing force). Assuming equal velocity (β≧0.9), the time spent in each half is the same and no net focusing or defocusing occurs. However, under semiconductor tooling conditions, if β≦0.5, the increase in velocity is significant and the ions spend less time in the defocusing field in the back half of the gap, resulting in net focusing. Therefore, in such cases, it is possible to generate a beamline without a quadrupole associated with each stage of the accelerating structure, thereby reducing space charge forces with focusing emanating from components of the accelerating structure (i.e., the accelerating electrodes of a given accelerating stage).

[0034] Removing the quadrupole elements from the linear accelerator stage may result in a reconfiguration of the drift tube assembly. In particular, in known ion implanter linear accelerators, the quadrupole elements are positioned at the location of the grounded drift tube (e.g., surrounding the grounded drift tube). The grounded drift tube tends to elongate at this location to support the quadrupole elements. With the quadrupole elements removed, the grounded drift tube may be sized according to other considerations, in particular, the length of the grounded drift tube may be shortened to a more compact configuration, where the value of the drift tube length (L) is based on the drift tube diameter (D), with L / D being less than 2, and in some cases, even 1.5. A comparison of Figures 1A and 1B shows the resulting relatively shortened length of the drift tube assembly.

[0035] Thus, this more compact configuration may involve a rotated resonator design, where a first resonator coupled to a first acceleration stage is rotated relative to a second resonator coupled to a second acceleration stage adjacent to the first acceleration stage. This rotated resonator design can be used to achieve a more compact arrangement of the resonators along the beamline so as not to limit the ability to reduce the length of the acceleration stages.

[0036] In some embodiments of the ion implanter, all acceleration stages of the linear accelerator may be configured without any quadrupole elements. In other embodiments of the ion implanter, one or more acceleration stages (e.g., two acceleration stages, three acceleration stages, five acceleration stages, ten acceleration stages, etc.) may include quadrupole elements, but one or more acceleration stages do not include quadrupole elements. Since the focusing effect of the acceleration stages varies with the relative velocity change, this focusing effect is strongest in the early (upstream) stages of the LINAC, where the relative velocity change is greatest. On the other hand, the space charge forces that necessitate steady-state focusing are strongest at relatively low velocities, so the potential advantages of various focusing structures and selective placement of quadrupoles in one or more stages may be realized on a case-by-case basis in accordance with various embodiments of the present disclosure.

[0037] FIG. 3 illustrates an exemplary process flow 300. In block 302, an ion beam is generated. The ion beam may include any suitable ions and may be generated in a beamline ion implanter. In block 304, the ion beam is converted from a continuous ion beam to a bunched ion beam, where the ion beam is propagated in a series of discrete ion packets. In block 306, the bunched ion beam is conducted through multiple acceleration stages of a linear accelerator. In block 308, an RF voltage is applied to at least one of the multiple acceleration stages without applying a quadrupole field, and the ion beam is focused by the acceleration stage.

[0038] In view of the above, at least the following advantages are achieved by the embodiments disclosed herein: By providing an approach to accelerating a bunched ion beam using RF accelerating voltages without the use of quadrupole elements, the present embodiments provide the advantage of avoiding the complexity and cost associated with quadrupole elements. A further advantage provided by the present embodiments is the ability to reduce the overall length of the acceleration stage and linear accelerator by eliminating quadrupole elements that may constrain the drift tube to be longer than necessary.

[0039] Although specific embodiments of the present disclosure have been described herein, the present disclosure is not limited thereto, as the art will permit, and the specification can be read in the same manner. Thus, 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 source and extraction system configured to generate an ion beam at a first energy; and a linear accelerator disposed downstream of the ion source and configured to receive the ion beam as a bunched ion beam, the linear accelerator accelerating the ion beam to a second energy greater than the first energy, the linear accelerator comprising a plurality of acceleration stages, a given acceleration stage of the plurality of acceleration stages: a drift tube assembly configured to transmit the ion beam; a resonator electrically coupled to the drift tube assembly; an RF power assembly coupled to the resonator and configured to output an RF signal to the resonator; wherein the given acceleration stage does not include a quadrupole element. An ion implantation system comprising:

2. The ion implantation system of claim 1 , wherein the linear accelerator comprises at least three acceleration stages.

3. The ion implantation system of claim 1 , wherein said multiple acceleration stages do not include a quadrupole element.

4. 2. The ion implantation system of claim 1, wherein the drift tube assembly comprises a first grounded drift tube, an AC drift tube assembly disposed downstream of the first grounded drift tube, and a second grounded drift tube disposed downstream of the AC drift tube assembly.

5. 5. The ion implantation system of claim 4, wherein at least one of the first grounded drift tube and the second grounded drift tube has a compact configuration having a drift tube length (L) and a drift tube diameter (D) such that L / D is less than 2.

6. 5. The ion implantation system of claim 4, wherein the AC drift tube assembly comprises a first AC drift tube and a second AC drift tube downstream of the first AC drift tube, the resonator being coupled at a first end to the first AC drift tube and the resonator being coupled at a second end to the second AC drift tube.

7. The ion implantation system of claim 1 , wherein the RF signal comprises a frequency between 13.56 MHz and 27.12 MHz.

8. 2. The ion implantation system of claim 1 , wherein the linear accelerator comprises a rotating resonator design, wherein a first resonator coupled to a first acceleration stage is rotated relative to a second resonator coupled to a second acceleration stage adjacent to the first acceleration stage.

9. 1. A method of operating an ion implanter, comprising the steps of: generating an ion beam; bunching the ion beam, where the ion beam is transformed into a plurality of bunched ion packets; accelerating the bundled ion packets through multiple acceleration stages of a linear accelerator to high ion energies; wherein said accelerating comprises: applying an RF signal to a drift tube assembly to accelerate the ion beam from an initial ion energy to a higher ion energy in at least one of the plurality of acceleration stages without applying a quadrupole field to the ion beam, wherein the ion beam is focused by the drift tube assembly; and Implanting the ion beam into a substrate after passing through the linear accelerator. A method comprising:

10. The method of claim 9 , wherein a plurality of said RF signals are applied to said plurality of acceleration stages, respectively, without applying a quadrupole field to said ion beam.

11. 10. The method of claim 9, wherein the multiple acceleration stages each comprise a drift tube assembly including a first grounded drift tube, an AC drift tube assembly disposed downstream of the first grounded drift tube, a second AC drift tube disposed downstream of the AC drift tube assembly, and a second grounded drift tube disposed downstream of the second AC drift tube.

12. 12. The method of claim 11 , wherein at least one of the first grounded drift tube and the second grounded drift tube has a compact configuration having a drift tube length (L) and a drift tube diameter (D) such that L / D is less than 2.

13. The method of claim 9 , wherein the RF signal comprises a frequency between 13.56 MHz and 27.12 MHz.

14. 1. A linear accelerator disposed within an ion implantation system, the linear accelerator comprising: A plurality of acceleration stages, at least one of the plurality of acceleration stages comprising: a drift tube assembly configured to receive and transport the ion beam as a bundled ion beam, the drift tube assembly including a triple gap configuration or a double gap configuration; a resonator electrically coupled to the drift tube assembly; wherein the at least one acceleration stage does not include a quadrupole element.

15. 15. The linear accelerator of claim 14, wherein the linear accelerator comprises at least three acceleration stages.

16. The linear accelerator of claim 14 , wherein the plurality of acceleration stages does not include a quadrupole element.

17. 15. The linear accelerator of claim 14, wherein one or more of the multiple acceleration stages includes a quadrupole element.

18. 15. The linear accelerator of claim 14, wherein the drift tube assembly comprises a first grounded drift tube, an AC drift tube assembly disposed downstream of the first grounded drift tube, and a second grounded drift tube disposed downstream of the AC drift tube assembly.

19. 20. The linear accelerator of claim 18, wherein the AC drift tube assembly comprises a first AC drift tube and a second AC drift tube downstream from the first AC drift tube, the resonator being coupled to the first AC drift tube at a first end and the resonator being coupled to the second AC drift tube at a second end.

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