HELICAL VOLTAGE STANDOFF

An insulator that has a helical protrusion spiraling around the shaft is disclosed. A lip is disposed on the distal end of the helical protrusion, creating regions on the shaft that are shielded from material deposition by the lip. By proper sizing of the threads, the helical protrusion and the lip, the line-of-sight to the interior wall of the shaft can be greatly reduced. This results in longer times before failure. This insulator may be used in an ion implantation system to physically and electrically separate two components.

FIELD

Embodiments of the present disclosure relate to an insulator, and more particularly a helical insulator for use in an ion implantation system.

BACKGROUND

Ion implantation is a common technique to introduce impurities into a workpiece to affect the conductivity of portions of that workpiece. For example, ions that contain elements in Group III, such as boron, aluminum and gallium, may be used to create P-type regions in a silicon workpiece. Ions that contain elements in Group V, such as phosphorus and arsenic, may be used to create N-type regions in the silicon workpiece. Of course, other species may also be used.

In some ion implantation systems, ions are generated in an ion source and are extracted through an extraction aperture. In some embodiments, one or more electrodes, which are electrically biased, are located outside the ion source, proximate the extraction aperture. The voltage applied to one of these electrodes serves to attract ions from within the ion source such that the ions exit the ion source through the extraction aperture.

Insulators are located between the ion source and each of the electrodes to maintain different voltages on each of these components. Additionally, insulators may be located in other locations, such as between conductive rods in an energy purity module (EPM), as feet for various sections or the system and other locations. Thus, the placement of the insulators is not limited. However, over time, deposition, which is caused by the material that is extracted from the ion source, begins to coat the insulators. Over time, the coating on the insulator may be sufficiently thick such that an electrical path forms along the exterior edge of the insulator. This may cause two of these components to be electrically shorted. In this scenario, the ion implantation system is taken off line so that the insulator can be cleaned or replaced. This reduces throughput and hurts efficiency.

Therefore, it would be advantageous if there were an insulator that could be used in an ion implantation system that was more resistant to these electrical shorts.

SUMMARY

An insulator that has a helical protrusion spiraling around the shaft is disclosed. A lip is disposed on the distal end of the helical protrusion, creating regions on the shaft that are shielded from material deposition by the lip. By proper sizing of the threads, the helical protrusion and the lip, the line-of-sight to the interior wall of the shaft can be greatly reduced. This results in longer times before failure. This insulator may be used in an ion implantation system to physically and electrically separate two components.

According to one embodiment, an insulator is disclosed. The insulator comprises a shaft having a first end and a second end; and a helical protrusion spiraling around the shaft, wherein the helical protrusion comprises a lip disposed at its distal end extending toward the second end. In some embodiments, the helical protrusion extends from the first end to the second end. In some embodiments, the helical protrusion extends from the first end toward the second end. In certain embodiments, an indentation is disposed between the helical protrusion and the second end. In certain embodiments, an indentation is disposed between the first end and the helical protrusion and between the second end and the helical protrusion. In some embodiments, a helical recess is disposed between adjacent threads of the helical protrusion, and wherein a portion of the helical recess is shielded by the lip. In some embodiments, pitch is defined as a distance between two adjacent threads of the helical protrusion, and the pitch comprises two portions, a total lip height defined as a distance from a bottom of a thread of the helical protrusion to a top of the lip, and an open height defined as a distance from the top of the lip to a bottom of an adjacent thread, and a ratio of the total lip height to the open height is between 0.75 and 10. In certain embodiments, wherein the ratio of the total lip height to the open height is between 2.5 and 10. In some embodiments, the open height is between 0.02 and 0.5 inches. In some embodiments, a width of the shaft varies over its length.

According to another embodiment, an ion implantation system is disclosed. The ion implantation system comprises an ion source; at least two electrodes disposed outside the ion source; and the insulator described above, disposed between the at least two electrodes to physically and electrically separate the at least two electrodes from each other.

According to a third embodiment, an insulator is disclosed. The insulator comprises a shaft having a first end and a second end; a helical protrusion spiraling around the shaft; and a sheath extending outward from the shaft and surrounding a portion of the shaft, wherein a sheath helical protrusion is disposed on an interior surface of the sheath facing the shaft; wherein at least one of the helical protrusion or the sheath helical protrusion comprises a lip disposed at its distal end. In some embodiments, the lip extends toward an opening between the sheath and the shaft. In some embodiments, the lip extends away from an opening between the sheath and the shaft. In certain embodiments, a lip is disposed on both the helical protrusion and the sheath helical protrusion. In some embodiments, the lip disposed on the helical protrusion and the lip disposed on the sheath helical protrusion extend in a same direction. In some embodiments, the insulator comprises a second sheath extending outward from the shaft and covering a second portion of the shaft.

According to another embodiment, an ion implantation system is disclosed. The ion implantation system comprises an ion source; at least two electrodes disposed outside the ion source; and the insulator described above, disposed between the at least two electrodes to physically and electrically separate the at least two electrodes from each other.

DETAILED DESCRIPTION

FIG.1shows an ion implantation system that may be used for implanting ions into a workpiece using an ion beam according to one embodiment.

The ion implantation system includes an ion source100comprising a plurality of chamber walls defining an ion source chamber. In certain embodiments, the ion source100may be an RF ion source. In this embodiment, an RF antenna may be disposed against a dielectric window. This dielectric window may comprise part or all of one of the chamber walls. The RF antenna may comprise an electrically conductive material, such as copper. An RF power supply is in electrical communication with the RF antenna. The RF power supply may supply an RF voltage to the RF antenna. The power supplied by the RF power supply may be between 0.1 and 10 kW and may be any suitable frequency, such as between 1 and 100 MHz. Further, the power supplied by the RF power supply may be pulsed.

In another embodiment, a cathode is disposed within the ion source chamber. A filament is disposed behind the cathode and energized so as to emit electrons. These electrons are attracted to the cathode, which in turn emits electrons into the ion source chamber. This cathode may be referred to as an indirectly heated cathode (IHC), since the cathode is heated indirectly by the electrons emitted from the filament.

Other embodiments are also possible. For example, the plasma may be generated in a different manner, such as by a Bernas ion source, a capacitively coupled plasma (CCP) source, microwave or ECR (electron-cyclotron-resonance) ion source. The manner in which the plasma is generated is not limited by this disclosure.

One chamber wall, referred to as the extraction plate, includes an extraction aperture. The extraction aperture may be an opening through which the ions1generated in the ion source chamber are extracted and directed toward a workpiece10. The extraction aperture may be any suitable shape. In certain embodiments, the extraction aperture may be oval or rectangular shaped.

Disposed outside and proximate the extraction aperture of the ion source100are extraction optics110. In certain embodiments, the extraction optics110comprise one or more electrodes. In certain embodiments, the extraction optics110comprises a suppression electrode111, which is negatively biased relative to the plasma so as to attract ions through the extraction aperture. The suppression electrode111may be electrically biased using a suppression power supply (not shown). The suppression electrode111may be biased so as to be more negative than the extraction plate of the ion source100. In certain embodiments, the suppression electrode111is negatively biased by the suppression power supply, such as at a voltage of between −3 kV and −15 kV.

In some embodiments, the extraction optics110includes a ground electrode112. The ground electrode112may be disposed proximate the suppression electrode111. The ground electrode112may be electrically connected to ground. Of course, in other embodiments, the ground electrode112may be biased using a separate power supply.

In other embodiments, the extraction optics110may comprise in excess of two electrodes, such as three electrodes or four electrodes. In these embodiments, the electrodes may be functionally and structurally similar to those described above, but may be biased at different voltages.

Each electrode in the extraction optics110may be a single electrically conductive component with an aperture disposed therein. Alternatively, each electrode may be comprised of two electrically conductive components that are spaced apart so as to create the aperture between the two components. The electrodes may be a metal, such as tungsten, molybdenum or titanium. One or more of the electrodes may be electrically connected to ground. In certain embodiments, one or more of the electrodes may be biased using an electrode power supply. The electrode power supply may be used to bias one or more of the electrodes relative to the ion source so as to attract ions through the extraction aperture. The extraction aperture and the apertures in the extraction optics110are aligned such that the ions1pass through apertures.

The electrodes in the extraction optics110may be separated, both physically and electrically, through the use of one or more insulators115. Further, in some embodiments, insulators115are also used to separate the ion source100from the suppression electrode111.

Located downstream from the extraction optics110is a mass analyzer120. The mass analyzer120uses magnetic fields to guide the path of the extracted ions1. The magnetic fields affect the flight path of ions according to their mass and charge. A mass resolving device130that has a resolving aperture131is disposed at the output, or distal end, of the mass analyzer120. By proper selection of the magnetic fields, only those ions1that have a selected mass and charge will be directed through the resolving aperture131. Other ions will strike the mass resolving device130or a wall of the mass analyzer120and will not travel any further in the system.

A collimator140may be disposed downstream from the mass resolving device130. The collimator140accepts the extracted ions1that pass through the resolving aperture131and creates a ribbon ion beam formed of a plurality of parallel or nearly parallel beamlets.

Located downstream from the collimator140may be an acceleration/deceleration stage150. The acceleration/deceleration stage150may be referred to as an energy purity module (EPM). The energy purity module is a beam-line lens component configured to independently control deflection, deceleration, and focus of the ion beam. For example, the energy purity module may be a vertical electrostatic energy filter (VEEF) or electrostatic filter (EF). Located downstream from the acceleration/deceleration stage150is the movable workpiece holder160.

In some embodiments, one or more lenses may be disposed along the beam line. A lens may be disposed before the mass analyzer120, after the mass analyzer120, before the collimator140or another suitable location.

The workpiece10is disposed on a movable workpiece holder160.

In certain embodiments, the forward direction of the ion beam is referred to as the Z-direction, the direction perpendicular to this direction and horizontal may be referred to as the first direction or the X-direction, while the direction perpendicular to the Z-direction and vertical may be referred to as the second direction or Y-direction.

Thus, in operation, the movable workpiece holder160moves in the second direction from a first position, which may be above the ion beam2to a second position, which may be below the ion beam2. The movable workpiece holder160then moves from the second position back to the first position. The ion beam2is wider than the workpiece10in the first direction, ensuring that the entirety of the workpiece10is exposed to the ion beam2.

In certain embodiments, sensors are used to monitor the ion beam. For example, Faraday cups may be used to measure the beam current at or near the workpiece. Other beam monitoring devices may also be employed. These other beam monitoring devices may include multipixel profilers, dose cups, and set up cups.

In addition to the use of insulators between the electrodes in the extraction optics, insulators115may also be used in conjunction with electrical feedthroughs, Faraday sensors, electrostatic cups, lenses and high voltage stacks. For example, insulators may be disposed in the acceleration/deceleration stage150to provide electrical feedthroughs for the rods in the EPM.

In other embodiments, the insulators may be used as electrical feedthroughs to supply voltage through the chamber walls of the ion source100.

In some embodiments, an insulator is used to isolate the one or more lenses from ground. In other embodiments, an insulator may be used to isolate the Faraday cups or beam monitoring devices from ground.

Of course, any component that is maintained at a voltage that is different from the voltage of surrounding components (or from ground) may be isolated using the insulator described herein.

In some embodiments, some of the ions or other material that are extracted from the ion source100may be deposited on the insulators115. This material may be electrically conductive, such that over time, a conductive path may form on the exterior surface of the insulator, causing the suppression electrode111to electrically short to the ion source100or the ground electrode112.

FIGS.2A-2Bshow a first embodiment of an insulator115that is resistant to the formation of this conductive path.FIG.2Bshows a cross-sectional view of the insulator115ofFIG.2A. The insulator115has a height205, which may be determined by the configuration of the ion implantation system. For example, insulators that are used for the extraction optics110may have a height205of between 1 and 3 inches and a width210of between 0.5 and 1 inches. Other insulators, such as those used to isolate other components, may have a height205of, for example, between 1 and 12 inches and a width210, which may be, for example, between 1 and 24 inches, although other dimensions are also possible. In certain embodiments, the shaft200of the insulator may be cylindrical such that the width210is also the diameter of the insulator115. However, in other embodiments, the shaft200of the insulator may be an oval cylinder, an elliptical cylinder, a cuboid or any other suitable shape. The shaft200of the insulator115has a first end220and a second end230. In some embodiments, the first end220has an interior threaded channel221, which may be disposed along the central axis201of the shaft200. Likewise, an interior threaded channel231may be disposed on the second end230. These interior threaded channels allow screws to be inserted so as to secure the insulator115in position. For example, screws may be used to secure the insulator115between the suppression electrode111and the ground electrode112.

The shaft200of the insulator115has a helical recess242that spirals from the second end230to the first end220. The interior wall250of the helical recess242may be the part of the shaft200having the smallest width. The portions of the shaft200that are not recessed may retain the same width as the first end220or the second end230. These portions of the shaft200that are not recessed may be referred to as the helical protrusion240. The helical protrusion240extends radially outward from the recessed regions. Thus, helical recess242and helical protrusion240are used to denote parts of the shaft200that have two different widths or diameters. In some embodiments, there is a single helical protrusion240that spirals from the first end220to the second end230. However, in other embodiments, additional helical protrusions240may be present. Although the helical protrusion240is continuous, throughout this disclosure, the term “thread” is used to describe a specific protrusion.

While the above description discloses that the helical protrusion240extends from the first end220to the second end230, other embodiments, which are shown inFIGS.7A-7C, are also possible. For example, the helical protrusion240may be separated from the first end220, as shown inFIG.7A, the second end230as shown inFIG.7B, or both ends as shown inFIG.7C. As shown inFIG.7C, the helical protrusion240may cover between 20% and 75% of the shaft200.

Additionally, in embodiments where the helical protrusion240does not extend to one end or both ends, there may be an indentation243in the shaft200that separates the helical protrusion240and the helical recess242from that end. In some embodiments, the indentation243has a width or diameter equal to that of the interior wall250. In other embodiments, the width of the indentation243may be larger or smaller than the width or diameter of the interior wall250.

In embodiments where the helical protrusion240does not extend to the second end230, the helical protrusion240extends from the first end220toward the second end230.

In all of these embodiments, the helical protrusion240extends from a first position at or near the first end220to a second position at or near the second end230. As described above, the first position may be at the first end220or a distance of between 5% and 25% of the length of the shaft200from the first end220. Similarly, the second position may be at the second end230or a distance of between 5% and 25% of the length of the shaft200from the second end230.

The helical protrusion240has a proximal end, which abuts the shaft200and a distal end opposite the proximal end. The distal end of the helical protrusion240may have a lip241that extends in a direction that is not radial and is toward the second end230. As described in more detail below, the lip241creates shielded regions in the helical recess242that do not have line-of-sight to the ion source100or the extracted ions.

FIGS.3A-3Cshow another embodiment of the insulator115.FIG.3Bshows a cross-sectional view of the insulator115ofFIG.3A, whileFIG.3Cis an expanded view of the helical protrusion. As described above, in some embodiments, the first end220has an interior threaded channel221, which may be disposed along the central axis201of the shaft200. Likewise, an interior threaded channel231may be disposed on the second end230. These interior threaded channels allow screws to be inserted so as to secure the insulator115in position. In this embodiment, the insulator is constructed with more rounded edges than appeared inFIGS.2A-2B. Specifically, the location where the helical protrusion240meets the helical recess242is rounded, rather than a sharp angle. Similarly, the location where the helical protrusion240meets the lip241is also rounded, rather than a sharp angle.

FIG.3Cshows many parameters associated with the helical protrusion240, the lip241and the helical recess242. Further, in this embodiment, the lip241extends further toward the second end230. An increase in the height of the lip241may result in a larger pitch and a smaller number of threads. Conversely, a smaller lip241allows for smaller pitch and a greater number of threads per inch.

First, as best shown inFIG.3C, the pitch of the helical protrusion240, which is defined as the distance from the bottom edge of one thread of the helical protrusion240to the bottom edge of the directly adjacent thread of the helical protrusion240, may be between 0.035 and 5.5 inches, although other values may be used. For example, in some embodiments, the pitch may be between 0.5 inches and 1.5 inches. That pitch is divided into two portions, the first portion, or total lip height270, is the region from the bottom edge of the helical protrusion240to the top of the lip241, while the second portion, or open height271, is the distance from the top of the lip241to the bottom edge of the adjacent helical protrusion240.

The lip height272is defined as the distance from the top edge of the helical protrusion240to the top of the lip241. The total lip height270is equal to the lip height272plus the thickness of the helical protrusion240. The helical protrusion240may have a thickness of between 0.02 and 1.0 inches, although other dimensions may be used. The thickness is defined as the dimension of the helical protrusion240that is parallel to the central axis201of the shaft200.

The open height271helps define the range of angles that have a line-of-sight to the interior wall250. In some embodiments, the open height271may be between 0.02 inches and 0.5 inches, although other dimensions may be used.

The maximum angle at which material still reaches the interior wall250is referred to as a. Looking atFIG.3C, it can be seen that angle α can be roughly defined as the arc tangent of open height271divided by the distance from the top of the lip241to the outer edge of the helical protrusion240. This can roughly be expressed as arctan(open height271/(protrusion distance275−separation distance276)). Alternatively, it may be approximated as the arctan (open height271/lip thickness274). The maximum angle α is less than 90° and is preferably as small as possible. In some embodiments, the maximum angle α may be between 7° and 35°. In other embodiments, the maximum a may be less than 20°. A smaller open height271reduces the maximum line-of-sight angle, but also brings the lip241in closer proximity to the adjacent bottom edge of the helical protrusion240. In some embodiments, the ratio of the total lip height270to the open height271may be as small as 0.75. In some embodiments, the ratio of the total lip height270to the open height271may be as large as 10. The portion of the interior wall250that is exposed to the line-of-sight includes the underside or bottom edge of the helical protrusion240, and the interior wall that is between the bottom edge of the helical protrusion240and aligned to the top of the lip241. Further, there is an exposed portion273of the interior wall250that is below the height of the top of the lip241that is also exposed. The length of the exposed portion273is determined based in part on the maximum angle of the line-of-sight, α.

The helical protrusion240extends outward from the interior wall250by a protrusion distance275, which may be between 0.1 and 1.25 inches. The lip241has a lip thickness274that may be between 0.02 inches and 0.30 inches, although other thickness are also possible. The lip241extends at an angle from the helical protrusion240. The angle, θ, represents the angle formed between the top edge of the helical protrusion240and the inner edge of the lip241. In some embodiments, this angle, θ, may be between 3° and 92°.

The separation distance276defines the distance from the innermost part of the lip241to the interior wall250of the helical recess242. This separation distance276also helps define the size of the exposed portion273. In other words, the greater the separation distance276, the larger the exposed portion273. In some embodiments, the separation distance276is related to the open height271, such that the ratio of separation distance276to the open height271is between 0.12 and 1.0, although other ratios may also be used.

The angle, θ, and the lip height272determine the amount of overhang277that exists. Overhang277is defined as the portion of the upper surface of the helical protrusion240that is vertically beneath the lip241. In this context, “vertically” refers to the direction of the central axis201. For example, if the lip241is vertical, there is no overhang. In some embodiments, the ratio of the overhang277to the lip thickness274of the lip241is between 0.125 and 0.75, although other ratios are also possible.

Shielded surface278, which is shown in crosshatch, represents that portion of the helical recess242, the helical protrusion240and the lip241that is shielded by the lip241and is therefore not in the line-of-sight of the ion source100. The shielded surface278is disposed in the region defined by the interior surface of the lip241and the upper surface of the helical protrusion240. The shielded surface278may also extend upward along the interior wall250of the shaft200, depending on the maximum angle α. The shielded surface278refers to any surface that is not directly visible from outside the insulator115.

The dimensions described above also affect the amount of rebound deposition. Rebound deposition is defined as deposition that is caused by material that bounced or was deflected from another surface. For example, looking atFIG.3C, rebound deposition may appear on the shielded surface278because of material that bounced from the exposed portion273of the interior wall250.FIGS.6A-6Bshow two different configurations which result in a different amount of rebound deposition.

In both configurations, the angle θ is kept constant. The difference is that the ratio of total lip height270to open height271is much greater inFIG.6B. This larger ratio creates a much smaller line-of-sight angle α. This results in a much smaller exposed portion273of the interior wall250and a much larger shielded surface278. In certain embodiments, the ratio of total lip height270to open height271may be 2.5 or greater. In certain embodiments, the ratio may be between 2.5 and 10. Furthermore, the smaller angle α also affects the angle at which material bounces from the exposed portion273. Consequently, as shown inFIG.6B, the amount of the shielded surface278that may be bombarded by rebound deposition is much smaller than that inFIG.6A.

FIGS.4A-4Dshows other embodiments of the insulator.FIG.4Bshows a cross-sectional view of the insulator ofFIG.4A. As described above, in some embodiments, the first end220has an interior threaded channel221, which may be disposed along the central axis201of the shaft200. Likewise, an interior threaded channel231may be disposed on the second end230. These interior threaded channels allow screws to be inserted so as to secure the insulator115in position.

In this embodiment, a sheath400is attached at the first end220of the shaft200and extends toward the second end230, but does not contact the second end230. Thus, the sheath400extends outward from the shaft200and surrounds a portion of the shaft200. In embodiments where the shaft is cylindrical, the sheath may be cup-shaped. In some embodiments, the distance between the second end230and the end of the sheath400may be 0.04 to 0.5 inches. The shaft200has a helical protrusion240.

The sheath400may have a thickness of 0.02 to 1.5 inches or more, although other dimensions are also possible. In some embodiments, such as that shown inFIG.4B, the interior wall of the sheath400also includes a sheath helical protrusion410. The sheath helical protrusion410extends toward the central axis201of the shaft200. The sheath helical protrusion410may also include a sheath lip411as shown inFIGS.4C-4D, which is similar to the lip241as shown inFIG.3C. In other embodiments, the sheath lip411may be omitted.

In some embodiments, the pitch of the sheath helical protrusion410may be the same as that of the helical protrusion240.

In certain embodiments, the protrusions of the shaft200and the sheath400are configured such that the threads of the helical protrusion240from the shaft200are disposed between two adjacent threads of the sheath helical protrusion410of the sheath400.

WhileFIGS.4A-4Dshow the sheath400as being cylindrical, it may have other shapes, such as an oval cylinder, an elliptical cylinder, a cuboid or any other suitable shape.

As described above, in some embodiments, the helical protrusion240extends from the first end220to the second end230. In other embodiments, the helical protrusion240may be separated from at least one of the ends, similar to the separation shown inFIGS.7A-7C.

In some embodiments where a sheath400is used, the helical protrusion240may include a lip241, as described above. As shown inFIG.4C, this lip241may extend downward, away from the opening between the sheath400and the shaft200. In another embodiment, shown inFIG.4D, this lip241may extend upward, toward the opening between the sheath400and the shaft200. Thus, in some embodiments, the insulator comprises the shaft200, helical protrusion240and lip241described with respect toFIGS.2A-2B and3A-3C, with the inclusion of a sheath400.

In some embodiments, the sheath helical protrusion410may also have a sheath lip411. The sheath lip411is similar to the lip241, described above, but is disposed on the sheath helical protrusion410, rather than the helical protrusion240. In some embodiments, the sheath lip411extends in the same direction as the lip241. Thus, inFIG.4C, the sheath lip411extends downward away from the opening between the sheath400and the shaft200. InFIG.4D, the sheath lip411extends upward toward the opening between the sheath400and the shaft200.

WhileFIGS.4C-4Dshow a lip on both the helical protrusion240and the sheath helical protrusion410, it is understood that in certain embodiments, only one of these helical protrusions has a lip. For example, there may be a sheath lip411and no lip241or a lip241and no sheath lip411.

FIGS.5A-5Eshow variations of the insulators. In all of these embodiments, the shaft200includes a helical protrusion spiraling from the first end to the second end. In addition, a lip241is extending from at least a portion of the helical protrusion240in each embodiment.

InFIG.5A, the width of the shaft200is not uniform. Rather, the shaft200is thicker in the middle than near the first end220and the second end230. In another embodiment (not shown), the shaft200may be thinner in the middle than near the first end and second end. In certain embodiments, the helical protrusion240changes protrusion distance275so that the outer width of the insulator remains constant. In other embodiments, the protrusion distance275may remain constant such that the outer width of the insulator varies.

FIG.5Bshows an insulator, where there are multiple lips extending from the helical protrusions240. Thus, there may be at least a first lip241aand second lip241bdisposed on the helical protrusion240. In other embodiments, the second lip241bmay extend inward from the first lip241a.

FIG.5Cshows the insulator with a top sheath420. In this embodiment, the top sheath420does not begin at the first end220. Rather, it only shields a top portion of the shaft. The top sheath420may begin at the midpoint of the shaft200, or at a different location.

FIG.5Dshows the insulator with a top sheath420and a bottom sheath430. In this embodiment, the bottom sheath430begins at the first end220and travels to a location near the midpoint of the shaft. The top sheath420begins at a location proximate the top of the bottom sheath430. In this way, the bottom sheath430shields the bottom portion of the shaft, while the top sheath420only shields a top portion of the shaft. In another embodiment, the top sheath420may extend downward from the second end230toward the midpoint of the shaft, while the bottom sheath430begins at the first end220and travels to a location near the midpoint of the shaft

FIG.5Eshows the insulator with a bottom sheath430. In this embodiment, the bottom sheath430begins at the first end220. However, it only shields a bottom portion of the shaft200. The bottom sheath430may terminate at the midpoint of the shaft200, or at a different location.

Although not shown, in other embodiments, the pitch and/or thickness of the helical protrusion240may change over the height of the insulator.

In all embodiments, the insulator115may be constructed from an insulating material. Suitable materials for use include aluminum oxide (Al2O3), zirconium oxide (ZrO3), yttrium oxide (YO3) or a combination of these. In some embodiments, resin bushings may be used. Due to the shape of the insulator, it may be preferable to construct the insulator using an additive manufacturing process, such as stereolithography. In addition to the ability to create the desired shapes, additive manufacturing also allows the insulator115to be constructed as one unitary component. In other words, the first end220, the second end230, the shaft200, the helical protrusions240and the lip241are all a single component.

The embodiments described above in the present application may have many advantages. The insulator includes two features that improve its performance. First, the insulator includes a helical protrusion that spirals around the shaft from the first end to the second end. This helical protrusion serves to increase the insulator's tracking length, which is a function of the pitch of the helical protrusion, and the width of the insulator. The greater the tracking length of an insulator, the more deposition needed to coat the insulator and cause it to fail. Because the helical design increases the tracking length over that of a standard insulator design, it will take longer for the insulator to be coated and fail, increasing both the lifetime of the insulator and the running time of the overall ion implantation system.

Second, the helical protrusion includes a lip. This lip further increases the tracking length and limits deposition's line of sight, creating shielded surfaces where ions and material are not likely to reach. The lip allows for the control over the angle at which deposition enters the shielded area. By minimizing this incident angle, the likelihood of deposition rebounding and redepositing deeper in the shielded area is greatly minimized. This reduces the possibility of a conductive path.

Additionally, the combination of the helical protrusion and the lip has additional benefits.FIG.8shows a comparison of an improved insulator800, having a helical protrusion801with a lip802on the left and an insulator810having concentric rings811, each with a lip812on the right. By disposing the lip802on a helical protrusion801, the lip802is continuous. In this way, temperature variation along the lip802may be reduced, especially as compared to the insulator810on the right that utilizes lips812on concentric rings811. Second, in the event that there are one or more point sources820of material for deposition, the insulator810having concentric rings811on the right will experience the same deposition pattern around the perimeter. However, with a helical protrusion801shown on the left, the deposition pattern on the improved insulator800varies as the helical protrusion801spirals.