Abstract:
An apparatus and method for trapping particles in a housing is disclosed. A high voltage terminal/structure is situated within a housing. A conductive material, having a plurality of holes, such as a mesh, is disposed a distance away from an interior surface of the housing, such as the floor of the housing, forming a particle trap. The conductive mesh is biased so that the electrical field within the trap is either non-existent or pushing toward the floor, so as to retain particles within the trap. Additionally, a particle mover, such as a fan or mechanical vibration device, can be used to urge particles into the openings in the mesh. Furthermore, a conditioning phase may be used prior to operating the high voltage terminal, whereby a voltage is applied to the conductive mesh so as to attract particles toward the particle trap.

Description:
This application claims priority of U.S. Provisional Patent Application Ser. No. 61/012,237, filed Dec. 7, 2007, the disclosure of which is hereby incorporated by reference. 
    
    
     FIELD 
     This disclosure relates to particle traps, and more particularly to a particle trap for an ion implanter. 
     BACKGROUND 
     An ion implanter is used to generate and direct ions towards a workpiece. A desired impurity material may be ionized in an ion source, the ions may be accelerated to form an ion beam of prescribed energy, and the ion beam may be directed at a front surface of the workpiece. In one application, the workpiece may be a semiconductor wafer where the energetic ions are embedded into the crystalline lattice of the semiconductor material of the wafer. The ion beam may be distributed over the wafer area by beam movement, by wafer movement, or by a combination of beam and wafer movement. 
     An ion implanter may have a terminal structure. The terminal structure may sometimes be referred to in the art as a “terminal” or “high voltage terminal” and is fabricated of conductive material such as metal. The terminal structure may have varying geometries that define a terminal shape. The ion source is contained within the terminal structure. The terminal structure may be energized to a terminal voltage to increase the acceleration of the ions from the ion source. The terminal structure, as well as other components and sub-systems of the ion implanter, are disposed within a grounded enclosure. Thus, the grounded housing protects personnel from high voltage dangers when the ion implanter is running. 
     As the terminal structure is energized, the presence of excessive amounts of particles and/or contaminants, about the terminal structure can adversely affect operational reliability of the ion implanter. These particles can include, but not be limited to, dirt, dust, debris and other types of particles such as metallic and non-metallic particles. For instance, random failures and voltage breakdowns may occur at less than desired terminal voltage levels. 
     Accordingly, there is a need in the art for an ion implanter having a particle trap to overcome the above-described inadequacies and shortcomings. 
     SUMMARY 
     The shortcomings of the prior art are overcome by the apparatus and method of the present disclosure. A high voltage terminal is situated within a housing/enclosure. A conductive material having a plurality of holes, such as a mesh, is disposed a distance away from an interior surface of the housing, such as the floor of the housing, forming a particle trap. The conductive mesh can be grounded in one embodiment, where the field created by the terminal voltage within the trap is negligible, allowing particles to fall into the trap. In another embodiment, the conductive mesh is biased so that the electrical field within the trap is either non-existent or pushing toward the floor, so as to retain particles within the trap. Additionally, a particle mover, such as a fan or mechanical vibration device, can be used to urge particles into the openings in the mesh. Furthermore, a conditioning phase may be used prior to operating the high voltage terminal, whereby a voltage is applied to the conductive mesh, while no voltage is applied to the terminal, so as to attract particles toward the mesh. In another embodiment, surface treatments can be applied to the terminal surfaces, and/or the ground surfaces to create areas where the electrostatic field is low, creating less attractive force on the particle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which like elements are referenced with like numerals, and in which: 
         FIG. 1  is a plan view of a block diagram of an ion implanter; 
         FIG. 2  is a perspective view of the terminal structure of  FIG. 1 ; 
         FIG. 3  is a partial cross sectional view taken along the line A-A of  FIG. 2  illustrating a particle trap consistent with one embodiment; 
         FIG. 4  is a partial cross sectional view of another embodiment of a particle trap having a particle mover; 
         FIG. 5  is a partial cross sectional view of another embodiment consistent with  FIG. 4  where the particle mover is a fan; 
         FIG. 6  is a partial cross sectional view of another embodiment consistent with  FIG. 4  where the particle mover is a mechanical structure to vibrate a conductive mesh of the particle trap; 
         FIG. 7  is a partial cross sectional view of another embodiment of a particle trap having a power supply coupled to a conductive mesh of the particle trap; 
         FIG. 8  is a flow chart of operations consistent with an embodiment of the disclosure; 
         FIG. 9  is a partial cross sectional view of another embodiment in which the high voltage terminal has perforated surfaces; and 
         FIG. 10  is a partial cross sectional view of another embodiment in which the floor has dimples. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure is described herein in connection with an ion implanter. However, this disclosure can be used with other apparatus having high voltage components where particles may adversely affect the performance of the apparatus. Thus, the disclosure is not limited to the specific embodiments described below. 
     Turning to  FIG. 1 , a block diagram of an ion implanter  100  including a particle trap consistent with this disclosure is illustrated. The ion implanter  100  is but one example of an ion implanter and those skilled in the art will recognize other ion implanters that may include a particle trap consistent with this disclosure. The ion implanter  100  includes a housing  112  defining a housing cavity, or air gap  144 . The housing  112  may also be referred to as an enclosure and is typically grounded. Disposed within the housing cavity  144  is a terminal structure  104  which may sometimes be referred to in the art as a “terminal” or a “high voltage terminal.” 
     The ion implanter  100  may also include an ion source  102 , a gas box  106 , an acceleration column  119 , a mass analyzer  120 , a aperture  122  having a mass slit  123 , a scanning system  124 , an angle corrector  126  and a controller  118 . The ion source  102  is configured to provide an ion beam  152 . The ion source  102  may include an arc chamber that, in one instance, accepts gas from the gas box  106 . The gas box  106  may provide a source of gas to be ionized to the arc chamber. Another source of gas to be ionized may be provided by a vaporizer that is configured to vaporize a solid dopant material. In addition, the ion source  102  may include arc, filament, and bias power supplies necessary for operating the ion source  102 . The construction and operation of ion sources and the gas box are well known to those skilled in the art. 
     The acceleration column  119  accelerates the ion beam  152 . The mass analyzer  120  deflects ions so that ions of a desired species pass through the mass slit  123  of the aperture  122  and undesired species do not pass through the mass slit  123 . The mass analyzer  120  may deflect ions of the desired species by 90 degrees and deflect ions of undesired species by differing amounts due to their different masses. A scanning system  124  positioned downstream from the mass slit  123  may include scanning electrodes  125  for scanning the ion beam  152  to produce a scanned ion beam having ion trajectories which diverge from a scan origin  160 . 
     An angle corrector  126 , such as an angle corrector magnet in one embodiment, deflects ions of the desired ion species to convert diverging ion beam paths to nearly collimated ion beam paths having substantial parallel ion trajectories. In one embodiment, the angle corrector  126  may deflect ions of the desired ion species by 45 degrees. 
     An end station may support one or more workpieces in the path of the ion beam  152  such that ions of the desired species strike the workpiece  140 . The workpiece  140  may be supported by a platen  142 . The end station  128  may include other components and sub-systems known in the art such as a workpiece handling system to physically move the workpiece  140  to and from the platen  142  from various holding areas. When the wafer handling system moves the workpiece  140  to the platen  142  from a holding area, the workpiece  140  may be clamped to the platen  142  using known techniques, e.g., electrostatic wafer clamping where the wafer is clamped to the platen with electrostatic forces. The end station may also include a mechanical scanning system to drive the workpiece  140  in a desired fashion. 
     The controller  118  may receive input data from components of the ion implanter  100  and control the same. For clarity of illustration, input/output paths from the controller  118  to components of the ion implanter  100  are not illustrated in  FIG. 1 . The controller  118  can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller  118  can also include other electronic circuitry or components, such as application specific integrated circuits, other hardwired or programmable electronic devices, discrete element circuits, etc. The controller  118  may also include user interface devices such as touch screens, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the ion implanter  100 . The controller  118  may also include communication devices and data storage devices. 
     The ion beam  152  provided to a surface of the workpiece  140  may be a scanned ion beam. Other ion implantation systems may provide a spot beam or a ribbon beam. The spot beam in one instance may have an approximately circular cross-section of a particular size depending on the characteristics of the spot beam. The ribbon beam may have a large width/height aspect ratio and may be at least as wide as the workpiece  140 . The scanner  124  would not be required for systems using a ribbon beam or a stationary spot beam. The workpiece  140  can take various physical shapes such as a common disk shape. In one instance, the workpiece  140  can be a semiconductor wafer fabricated from any type of semiconductor material such as silicon. 
     The ion source  102  may be positioned within the terminal cavity  110  defined by the terminal structure  104 . An extraction power supply  107  may be coupled to the ion source  102 . The extraction power supply  107  may provide a voltage level (Vx) to accelerate and extract ions from the ion source  102 . In one embodiment, the extraction power supply may provide a voltage (Vx) in the range of 20 kV to 120 kV. 
     An acceleration power supply  109  may be coupled between the terminal structure  104  and the grounded housing  112  so as to bias the terminal structure  104  at a positive voltage (Va) with respect to ground. In one embodiment, the acceleration power supply  109  may provide an additional voltage level (Va) that may have a maximum voltage in the range of 200 kV to 1,000 kV. Accordingly, the terminal structure  104  may be energized, in some instances, to a high voltage between 200 kV and 1,000 kV. In other instances, the terminal structure  104  may not be energized at all or energized to only nominal values, depending on the desired energy of the ion beam  152 . Although only one acceleration power supply  109  is illustrated for clarity of illustration, two or more power supplies may be utilized to provide the desired maximum high voltage level (Va). 
     During operation of the ion implanter  100 , the terminal structure  104  may be energized to high voltage levels depending on the desired energy level of the ion beam  152 . Particles including, but not be limited to, dirt, dust, debris and other types of particles such as metallic and non-metallic particles may be present on the terminal surface, within the air gap  111 , or in the terminal cavity  110 . The presence of such particles can cause voltage breakdown within the terminal structure  104  thus degrading the energy performance range of the ion implanter  100 . 
     Turning to  FIG. 2 , a perspective view of the terminal structure  104  of  FIG. 1  is illustrated. The terminal structure  104  may include a base, one or more upstanding sidewalls coupled to the base, and a top or ceiling  202  coupled to the one or more upstanding sidewalls. Although illustrated as a solid piece, the top  202 , the base or the sidewalls of the terminal structure may also be fabricated of a plurality of spaced conductors forming a type of conductor mesh to allow air to flow through the openings of the mesh. 
     In general, none, one or more insulated conductors may be disposed about portions of the exterior surface of the terminal structure  104  that have excess electric stress. In the embodiment of  FIG. 2 , a top insulated conductor  103  is disposed proximate the entire periphery of a top edge of the terminal structure  104 , and a bottom insulated conductor  203  is disposed proximate the entire periphery of a bottom edge  272 . A plurality of brackets may be coupled to the terminal structure  104  and the associated insulated conductors  103  and  203  to support the insulated conductors  103  and  203  proximate an exterior portion of the terminal structure. 
     The insulated conductors  103 ,  203  include an insulator with a dielectric strength greater than 75 kilovolts (kV)/inch disposed about a conductor. The insulated conductors  103 ,  203  may drop a high proportion of the terminal voltage within the insulated conductors  103 ,  203 . Hence, the insulated conductors  103 ,  203  reduces the electric stress in the air gap  111  between the terminal structure  104  and the housing  112  and helps to promote a more uniform electric field within the air gap  111  compared to terminal structures with no such insulated conductors. In other words, the insulated conductor  103  may function as an electrical stress shield. Therefore, the terminal structure  104  may be energized to higher voltage levels within the same reasonably sized grounded housing  112 . 
     Turning to  FIG. 3 , a partial cross sectional view taken along the line A-A of  FIG. 2  illustrates a particle trap  304  consistent with one embodiment of the disclosure. The terminal structure  104  may be supported by insulator legs  310  to a floor  312  of the housing  112 . A cross sectional view of the insulated conductor  203  of  FIG. 2  is also illustrated having a conductor  301  surrounded by an insulator  303 . A sidewall  308  and floor  312  of the housing  112  is also illustrated. 
     Advantageously, a conductive material having a plurality of openings, such as a conductive mesh,  302  is disposed a distance away from an interior surface of the housing, such as the floor  312 , a sidewall  308  or the ceiling, to define a particle trap  304  between the conductive material  302  and the interior surface. In certain embodiment, the particle trap is created between the conductive material  302  and the floor  312 . In the absence of electric fields, particles positioned proximate the terminal structure  104  tend to fall due to the force of gravity towards the conductive material  302  as illustrated by arrows  330 ,  332 . The conductive material  302  has a plurality of openings sized to permit the passage of particles  324  therethrough. In one embodiment, the conductive material  302  is a mesh, which may be fabricated of ⅛ inch diameter wire spaced at ⅝ inch apart and may be positioned about a distance of 1.5 inches above the floor  312 . The conductive mesh  302  may also be fabricated of materials that have sufficient mechanical strength such that personnel that enter the housing cavity  144  may walk on the conductive mesh  302  without damaging the same. Materials such as fencing may also be utilized. In other embodiments, a metal sheet of sufficient thickness and strength with a sufficient number of openings through which particles can pass may be used. In some embodiments, it is advantageous that the ratio of the surface area of the conductive material to the total area to be covered is as small as practical. In other words, the material should have as many openings as is practical to minimize the surfaces on which particles may rest. Although the term “conductive mesh” is used throughout this disclosure, any surface having a conductive material with a plurality of openings through which particles may pass may be used. Thus, the disclosure should not be limited to a specific embodiment. In the embodiment of  FIG. 3 , the conductive mesh  302  may be grounded. In this embodiment, the particle trap  304  defines an area of lower electric field strength so that particles  355  trapped therein tend to remain in the trap even when the terminal structure  104  is energized to high voltage levels. 
     Turning to  FIG. 4 , a partial cross sectional view of another embodiment of a particle trap  304  is illustrated. Compared to the embodiment of  FIG. 3 , the particle trap  304  has a particle mover  402  configured to urge particles towards a plurality of openings in the conductive mesh  302 . In this way, any particles that are in the housing cavity or resting on a top surface of the conductive mesh  302  would tend to be urged towards and through the plurality of openings in the conductive mesh  302 . An adhesive tape  406  may also be disposed on at least a portion of the floor  312  to assist in retaining particles in the trap. The adhesive tape  406  may include, but not be limited to, elastomers, polymers, or rubbers with a high particle sticking coefficient and a low outgas in vacuum. The adhesive tape  406  as well as the particle trap  304  may be cleaned during a preventative maintenance time. The adhesive tape  406  may also be replaced at other times during preventative maintenance. A disposable adhesive tape  406  can reduce the cleaning time for the particle trap  304 . The adhesive can be applied in combinations of other figures shown within. 
     Turning to  FIG. 5 , a partial cross sectional view of another embodiment of a particle trap  304  consistent with  FIG. 4  is illustrated where the particle mover  402  includes at least one fan  502 ,  504 . The fans  502 ,  504  include a motor and a blade as is known in the art and are configured to blow particles towards the plurality of openings in the conductive mesh  302 . Although two fans  502 ,  504  are illustrated, only one fan may be needed depending on differing parameters such as the area of the conductive mesh, and the strength of the fan. The fan  504  may be displaced in a vertical direction from the conductive mesh to urge particles substantially downward towards openings in the conductive mesh  302 . The fan  502  may be positioned to urge particles across the conductive mesh  302  so that particles that positioned on a top surface of the conductive mesh  302  tend to fall into openings in the conductive mesh  302 . 
     Turning to  FIG. 6 , a partial cross sectional view of another embodiment of a particle trap  304  consistent with  FIG. 4  is illustrated where the particle mover  402  is a mechanical device coupled to the conductive mesh  302  to vibrate the conductive mesh, for example in the direction  612 . In this way, particles that are positioned on a top surface of the conductive mesh  302  tend to fall into openings in the conductive mesh  302 . The mechanical device may include a motor  602  having an output shaft  604  and a drive train  606  coupled to the output shaft  604  and the conductive mesh  302 . The motor  602  is configured to drive the output shaft  604  and the drive train  606  to vibrate the conductive mesh  302 . One or more fans  502 ,  504  of  FIG. 5  may also be present to complement the mechanical vibration of the conductive mesh. Depending on the direction and distance of vibration of the conductive mesh  302 , sufficient clearance between the conductive mesh  302  and surrounding surfaces such as a sidewall  308  of the housing  112  should be provided. 
       FIG. 7  illustrates a partial cross sectional view of yet another embodiment of a particle trap consistent with the disclosure. As opposed to grounding the conductive mesh as previously detailed, the particle trap  304  of  FIG. 7  includes a power source  702  electrically coupled to the conductive mesh  302  to energize the conductive mesh during certain time intervals as is further detailed with respect to  FIG. 8 . 
     Turning to  FIG. 8 , a flow chart  800  of operations consistent with an embodiment of the disclosure is illustrated. The operations  800  detail a conditioning process that may be utilized before operation of the ion implanter  100 . The terminal structure of the ion implanter may be grounded  802 . Power may then be supplied to the conductive mesh to attract particles towards the particle trap in operation  804 . Such power may be supplied by the power supply  702  to the conductive mesh  302  as illustrated in  FIG. 7 . In some embodiments, the voltage applied to the conductive mesh may be about 100 kV. If an attraction time interval has not expired  806 , power is continually supplied to the conductive mesh. In some embodiments, an attraction time of roughly 10-15 minutes is used to allow sufficient time to allow particles to migrate to the trap. Other attraction times and voltages are also within the scope of the disclosure. If the attraction time interval has expired, the conditioning process inquires if a particle mover is present  808 . If a particle mover is not present, the conditioning cycle is complete and the ion implanter is free to operate. If a particle mover is present, the particle mover is activated  812 . If the particle mover has not been activated for a desired particle moving time interval  814 , then the process continues to operate the particle mover. If the particle mover has been activated for the desired moving time interval  814 , then the conditioning cycle is complete and the ion implanter is free to operate. Alternatively, if a particle mover is present it may be activated at the same time that power is supplied to the conductive mesh. 
     While  FIG. 8  assumes that the high voltage terminal is grounded during the conditioning process, this is not a requirement. Alternatively, the voltage applied to the conductive mesh can be much greater than that applied to the high voltage terminal. Both approaches will result in a electrostatic field within the housing wherein the more positive voltage is located near the trap. 
     Alternatively or additionally, other modifications can be made to further reduce the amount of particles in the high voltage environment. Combinations of the figures above can be utilized as systems within implanter  100 . 
     As described above, during normal operation, the conductive mesh may be held at the same potential as the floor of the housing. However, in another embodiment, the enclosed region defined between the conductive mesh and the floor is not maintained at zero electrostatic field. Rather, a field is created which continues to attract particles already in the trap away from the mesh and toward the floor. This can be achieved by applying a negative voltage to the conductive mesh during normal operation. Alternatively, a positive voltage can be applied to the floor. In either case, the localized electrostatic field within the trap draws particles already in the trap toward to the bottom surface, thereby reducing the possibility that particles drift out of the trap, into the electrostatic field and toward the high voltage terminal. This additional field can be provided either by using the power supply  702  (as shown in  FIG. 7 ), or by the use of an additional power supply. 
     In another embodiment, a particle trap is constructed on or near the ceiling of the housing  112 . In certain embodiments, during the conditioning process, a positive voltage is applied to the ceiling, or to a conductive surface positioned proximate the ceiling. Particles within the housing are attracted toward the ceiling due to this applied electrostatic field. To retain these attracted particles, especially after the voltage has been removed, a sticky substance, such as an adhesive tape, may be applied to the ceiling or proximate surface. As described above, the adhesive tape may include, but not be limited to, elastomers, polymers, or rubbers with a high particle sticking coefficient and a low outgas in vacuum. The adhesive tape may be removed and replaced during preventative maintenance. Alternatively, a localized electrostatic filed within the particle trap can be used to draw the particles toward the ceiling. This ceiling-based particle trap can be used alone or in conjunction with the previously described floor-based particle trap. When used simultaneously, the conditioning process must be extended to allow each conductive surface to be independently charged. In other words, in the first part of the conditioning process, the upper mesh is energized to attract particles upward into the ceiling-based trap. After the upper ceiling-based trap has been energized for a sufficient amount of time, the upper mesh is deactivated, and the lower mesh is energized. Any remaining particles that were not captured by the ceiling-based trap are attracted downward and are retained in the particle trap below. The process illustrated in  FIG. 8  is then completed and the implanter  100  is ready for normal operation. The conditioning process used for the ceiling-based trap may follow the steps outlined in  FIG. 8 . 
     Alternatively, or additionally, traps can be applied to the sidewalls of the housing  112 . In other words, a particle trap may be disposed near any interior surface of the housing, where the expression “interior surface of the housing” includes the floor, the ceiling and the sidewalls. Particle traps located near the sidewalls may use adhesive trap as described above to retain the particles. Alternatively, a localized electrostatic field within the particle trap that draws particles toward the sidewall can be utilized. 
     In other embodiments, as shown in  FIG. 9 , the high voltage terminal  104  comprises one or more perforated surfaces  156 . Perforated surfaces  156  have less surface area than solid surfaces, and therefore provide less surface area to which particles can attach. Such perforations also allow particles, such as those resting atop the high voltage terminal, to be drawn to the floor-based particle trap and pass into and/or through the high voltage terminal. Additionally, a particle mover  567 , such as a fan, can be used to push particles away from the high voltage terminal  104 , and preferably toward the particle trap  304 , as illustrated by the arrows in  FIG. 9 . Alternatively, the particle mover  567  can draw particles into the structure  104 , where no electrostatic field exists. Either scenario reduces the number of particles in contact with the outer surface of the terminal  104 . 
       FIG. 10  shows a second embodiment of a floor-based trap. In this embodiment, the floor  900  contains a number of depressions or dimples  910 . The surface irregularities affect the localized electrostatic field in that area. Specifically, the field in the depressions or dimples is at or near zero potential. Therefore, particles in those areas are not attracted toward the high voltage terminal. Thus, particles which fall into the depressions tend to remain in those depressions, even in the presence of an electrostatic field. In further embodiments, the conditioning process illustrated in  FIG. 8  can be utilized with this floor. Additionally, particle movers, such as fans and devices that cause mechanical vibration of the floor, can be used in conjunction with this embodiment. 
     Accordingly, there is provided a particle trap for an ion implanter. The particle trap creates a region of low electric field so that particles present in the trap tend to remain in the trap. This improves reliability of high voltage performance of the ion implanter. A particle trap consistent with the disclosure is not limited to ion implanters and may also be used in other high voltage apparatus. For example, other equipment used in the processing of semiconductor materials which require a portion of the machine to be at high voltages may make use of this trap. 
     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes.