Abstract:
A method of reducing foreign material contamination of a substrate in an ion beam system and an ion beam system. The system, including: a vacuum chamber having an ion beam axis; a substrate chamber free to tilt about a tilt axis, the tilt axis orthogonal to and intersecting the ion beam axis; a flexible bellows connecting an opening in the substrate chamber and an opening in the vacuum chamber, both openings co-axially aligned with the ion beam axis, the bellows providing a vacuum seal between the substrate chamber and the vacuum chamber; and a hollow foreign material shield open at a top proximate to the vacuum chamber and a bottom proximate to the substrate chamber, the foreign material shield located between the ion beam axis and the flexible bellows, the top and bottom of the foreign material shield co-axially aligned with the ion beam axis.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to the field of ion beam tooling; more specifically, it relates to an apparatus for bombarding or implanting ions in a substrate. 
   2. Background of the Invention 
   Fabrication of modern semiconductors utilize ion beam bombardment of charged species into a substrate to introduce impurities into the substrate in a very precise and controllable way. However, ion beam bombardment tools can generate foreign materials as particles or films that can contaminate the substrate being fabricated as well the ion bombardment. This can lead to poor quality product or yield loss or both. Therefore, there is a need for reducing foreign material contamination of substrates in ion beam systems. 
   SUMMARY OF INVENTION 
   A first aspect of the present invention is an ion beam system, comprising: a vacuum chamber having an ion beam axis; a substrate chamber free to tilt about a tilt axis, the tilt axis orthogonal to and intersecting the ion beam axis; a flexible bellows connecting an opening in the substrate chamber co-axially aligned with the ion beam axis and an opening in the vacuum chamber co-axially aligned with the ion beam axis, the bellows providing a vacuum seal between the substrate chamber and the vacuum chamber; and a hollow foreign material shield open at a top proximate to the vacuum chamber and a bottom proximate to the substrate chamber, the foreign material shield located between the ion beam axis and the flexible bellows, the top and bottom of the foreign material shield co-axially aligned with the ion beam axis. 
   A second aspect of the present invention is a method of reducing foreign material contamination of a substrate in an ion beam system, comprising: providing a vacuum chamber having an ion beam axis; providing a substrate chamber free to tilt about a tilt axis, the tilt axis orthogonal to and intersecting the ion beam axis; providing a flexible bellows connecting an opening in the substrate chamber co-axially aligned with the ion beam axis and an opening in the vacuum chamber co-axially aligned with the ion beam axis, the bellows providing a vacuum seal between the substrate chamber and the vacuum chamber; and providing a hollow foreign material shield open at a top proximate to the vacuum chamber and a bottom proximate to the substrate chamber, the foreign material shield located between the ion beam axis and the flexible bellows, the top and bottom of the foreign material shield co-axially aligned with the ion beam axis. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1A  a schematic side view of an ion beam system according to a first embodiment of the present invention; 
       FIG. 1B  is a diagram illustrating the degrees of freedom of a substrate loaded into the ion beam system of  FIG. 1A ; 
       FIG. 2A  is detailed cross-sectional view of a bellows area of the ion beam tool of  FIG. 1A ; 
       FIG. 2B  is a detailed cross-sectional view of an electron tool of the ion beam tool of  FIG. 1A ; 
       FIG. 3A  is a top view and  FIGS. 3B and 3C  are side view through line  3 B/ 3 C— 3 B/ 3 C of  FIG. 3A  of a first foreign material shield according to the present invention; 
       FIG. 4A  is a top view and  FIG. 4B  is a side view through line  4 B— 4 B of  FIG. 4A  of a second FM shield according to the present invention; 
       FIG. 5A  is a top view and  FIG. 5B  is a side view through line  5 B— 5 B of  FIG. 5A  of a third FM shield according to the present invention; 
       FIG. 6A  is a top view and  FIG. 6B  is a side view through line  6 B— 6 B of  FIG. 6A  of a fourth FM shield according to the present invention; 
       FIG. 7A  is a top view and  FIG. 7B  is a side view through line  7 B— 7 B of  FIG. 7A  of a fifth FM shield according to the present invention; 
       FIG. 8A  is a top view and  FIG. 8B  is a side view through line  8 B— 8 B of  FIG. 8A  of a sixth FM shield according to the present invention; 
       FIG. 9A  is a top view and  FIG. 9B  is a side view through line  9 B— 9 B of  FIG. 9A  of a seventh FM shield according to the present invention; and 
       FIG. 10  is detailed cross-sectional view of a bellows area of an ion beam tool according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The term “ion beam system” is defined to be any tool that generates a beam of charged atoms or molecules and directs that charged species to the surface of or into the body of a substrate. Examples of ion beam systems include but is not limited to ion implantation tools and ion milling tools. 
     FIG. 1A  a schematic side view of an ion beam system according to a first embodiment of the present invention. In  FIG. 1A , an ion beam system  100  includes an ion source  105 , an extractor  110  (which includes an extraction aperture), a first beam focuser  115  an exit aperture  120 , a beam analyzer  125  (in one example, an electromagnet), a first defining aperture  130 , a pumping chamber  135 , a second defining aperture  140 , a beam sampling section  145  (which includes a flag aperture), a second beam focuser  150 , an electro-magnetic reflector (EMR) aperture  155 , a secondary emission control assembly  160  (which includes an electron shower aperture  165 ), an electron shower tube  170 , a substrate chamber  175 , and an Yθ-stage  180 . Second defining aperture  140 , beam sampling section  145 , second beam focuser  150 , EMR aperture  155 , and secondary emission control assembly  160  are housed within a vacuum chamber  185 . Substrate chamber  175  is connected to vacuum chamber  185  by a bellows  190 . A foreign material (FM) shield  195  is positioned between electron shower electron shower tube  170  and bellows  190 . Electron shower tube  170  is negatively charged. 
   In operation, an ion plasma is generated within ion source  105  and ions extracted from the ion source by extractor  110  to generate an ion beam  200  (dashed lines). After being focused by first beam focuser  115 , ion beam  200  is passed through beam analyzer  125  where only ions of a predetermined charge to mass ratio exit through first defining aperture  130 . Ion beam  200  is now co-axially aligned with an ion beam axis  205  of ion beam system  100 . After passing through pumping chamber  135 , second defining aperture  140 , beam sampling section  145  second beam focuser  150 , EMR aperture  155 , secondary emission control assembly  160 , electron shower aperture  165  and electron shower electron shower tube  170 , ion beam  200  strikes substrate  210  on Yθ stage  180 . 
   In one example, ion beam  200  comprises charged species containing phosphorus, boron, arsenic, germanium, carbon, nitrogen, helium or combinations thereof. 
   Turning to  FIG. 1B ,  FIG. 1B  is a diagram illustrating the degrees of freedom of a substrate loaded into the ion beam system of  FIG. 1A . Ion beam axis  205  defines a Z-direction. A Y-direction is defined as a direction orthogonal to the Z-direction and an X-direction is defined as a direction orthogonal to both the Z-direction and the Y-direction. The Y-direction defines a horizontal direction and the Z-direction defines a vertical direction. The Z-direction and the Y-directions are within the plane of the drawing, the X-direction goes into and extends out of the plane of the drawing. Substrate chamber  175  can tilt about both an α axis and a β axis. The degree of tilt for both the α axis and the β axis may be positive or negative, but is limited by the mechanical constraints of the system, particularly bellows  190 , FM shield  195  and electron shower tube  170 . The α axis is parallel to the X-direction, orthogonal to the both the Z-direction and the Y-direction and intersects ion beam axis  205 . The β axis is parallel to the Y-direction, orthogonal to the both the Z-direction and the X-direction and intersects ion beam axis  205 . Yθ stage  180  (see  FIG. 1A ) can move in the Y-direction and rotate in about a θ axis. The θ axis is parallel to the Z-direction and orthogonal to the both the Y-direction and the X-direction. 
   Returning to  FIG. 1A , FM shield  195  is fixed to substrate chamber  175  and thus tilts when the substrate chamber is tilted and that electron shower tube  170  is fixed to vacuum chamber  185  and does not tilt when the substrate chamber is tilted. The entire path of ion beam  200  must be kept at high vacuum during operation of ion beam system  100 . Thus the need for bellows  190  becomes apparent if the vacuum integrity of ion beam system is to be maintained as substrate chamber  175  is tilted. The fact that bellows  190  flexes causes generation of foreign material as described infra. 
     FIG. 2A  is detailed cross-sectional view of the bellows area of ion beam tool  100  of  FIG. 1A . In  FIG. 2A , bellows  190  is seen to attach to substrate chamber  175  by a flange  215  and to vacuum chamber  185  by a flange  220 . Bellows  190  is in physical, electrical and thermal contact with flanges  215  and  220  and flanges  215  and  220  are in physical, electrical and thermal contact with substrate chamber  175  and vacuum chamber  185  respectively. An outer surface  225  adjacent to a bottom surface  230  of FM shield  195  is in physical, electrical and thermal contact with flange  215 . Thus when FM shield  195  comprises an electrically conducive material, the FM shield is in electrical contact with substrate chamber  175  and when FM shield  195  comprises an thermally conducive material, the FM shield is in thermal contact with substrate chamber  175 . FM shield  195  may comprise a material that is both thermally and electrically conductive. Suitable materials for FM shield  195  include but is not limited to aluminum, stainless steel, ceramics (examples of which include boron nitride, aluminum oxide, aluminum silicate), silicon carbide, carbon, silicon and high temperature polymers. Other non-magnetic materials may be used as well, such as other metals. If magnetic materials are used, it must be ensured that the dimensions of FM shield  195  are such that the magnetic fields induced in the FM shield does not adversely effect ion beam diameter, ion beam cross-section distributions or the centrality of the ion beam relative to ion beam axis  205 . 
   When FM shield  195  is a thermally conductive material, and if substrate chamber  175  is a thermal and electrical conductor (such as stainless steel or aluminum), the FM shield will act as a low temperature getter (it is heat sunk at room temperature, about 60° F. to about 70° F.) relative to the temperature of the internal vacuum (more correctly the temperature of the gas molecules remaining in the vacuum, about 1500° C. to about 3000° C.) as well as other components such as electron shower tube  170 . 
   There are two dimensions to which FM shield  195  may conform. The first is a distance A between a top surface  235  of FM shield  195  and flange  220  and the second is a distance B from an inner surface  240  adjacent to top surface  235  of FM shield  195  and an outer surface  250  of electron shower tube  170 . The distances A and B may be adjusted such that at maximum values of tilt angles α and β (see  FIGS. 1A and 1B ), top surface  235  of FM shield  195  does not come into contact with outer surface  250  of electron shower tube  170 . As A decreases B may be allowed to decrease and vice versa within the limits that B can not be reduced to the point where the efficiency of pumping to maintain the vacuum in substrate chamber  175  is effected. C is the distance between flanges  215  and  220  and D 0  is the diameter of electron shower tube  170 . 
   Turning to  FIG. 2B ,  FIG. 2B  is a detailed cross-sectional view of electron shower tube  170 . Electron shower tube  170  has a grooved inner surface  255  and is made of an electrically conductive material (for example, graphite). The purpose of electron shower tube  170  is to maintain a space charge region  260  around ion beam  200  as the ion beam transitions from vacuum chamber  185  into substrate chamber  175 . Each grove  265  in grooved surface  255  includes a sloped top surface  270  and a horizontal bottom surface  275 . The purpose of grooves  265  is to allow foreign material  280  to collect on sloped top surfaces  270  while leaving horizontal bottom surface  275  exposed to maintain space charge region  260 . As foreign material  280  accumulates on inner sidewall  255  of electron shower tube  170 , the effectiveness of space charge region  260  (see  FIG. 2A ) diminishes. 
   Returning to  FIG. 2A , there are two sources of foreign material that may impinge on wafer  210 , that FM shield  195  reduces or eliminates. The first source is vapors and particles generated from ion beam  200  striking substrate  210 . If substrate  210  is a semiconductor wafer than the vapor and particles given off may include photoresist and other organic materials, metals, silicon and ion implanted species. These materials, in vapor form coat an inner surface  285  of bellows  190 , outer surface  250  and inner surface  255  of electron shower tube  170 . These coatings can then flake off inner surface  285  of bellows  190 , outer surface  250  and inner surface  255  of electron shower tube  170  and impinge on substrate  210 . Since FM shield  195  is colder than electron shower tube  170 , these vapors are attracted to the FM shield and much of the vapors that would end up coating electron shower tube  170  and bellows  190  are gettered by and end up coating the FM shield, particularly inside surface  240  of the FM shield. The physical placement of FM shield  195  further substantially blocks particles shedding from or flaking off the coating on inside surface  285  of bellows  190  as the bellows flexes as substrate chamber  175  is tilted (see  FIGS. 1A and 1B ). 
   The second source of foreign material is material from internal portions of the tool through which the ion beam passes (such as apertures) in the form of vapor or particles that is transported by the beam. Much of this material is trapped between outer surface  255  of FM shield  230  and inner wall  285  of bellows  190 . The smaller the dimensions A and/or B, the more of this second source material is prevented from impinging on substrate  210 . 
     FIG. 3A  is a top view and  FIGS. 3B and 3C  are side view through line  3 B/ 3 C— 3 B/ 3 C of  FIG. 3A  of a first FM shield according to the present invention. In  FIGS. 3A and 3B , it may be seen that FM shield  195  comprises a hollow cylindrical bottom portion,  290  joined to a narrower top hollow cylindrical top portion  295  by a hollow tapered transition portion  300 . Bottom portion  290 , top portion  295  and transition portion  300  are integrally formed as a single unit. FM shield  195  has a top circular opening  235 A defined by top surface  235  and a bottom circular opening  230 A defined by bottom surface  230 . The overall height of FM shield  195  is H 1 , the height of top portion  295  is H 2 , the height of transition region  300  is H 4 . The outside diameter of bottom portion  290  is D 1  and of top portion  295  is D 2 . The wall thickness of FM shield  195  is T 1 . When used in an ion beam system for ion implanting 200 mm wafer substrates H 1  ranges from about 2 inches to about 4.25 inches, H 2  ranges from about 0.4 inches to about 1.5 inches, H 3  is about 0.8 inches, H 4  ranges from about 0.7 to about 1.9 inches, D 1  is about 6.4 inches and D 2  ranges from about 5.8 inches to about 6.0 inches (however D 1  is always greater than D 2 ) and T 1  is about one eight of an inch. When FM shield  195  is installed in ion beam system  100  (see  FIG. 1A ) the center of diameters D 1  and D 2  are intersected by ion beam axis  205 . 
   While in  FIG. 3B , inside surface  240  of FM shield is smooth, in  FIG. 3C , it is seen that inside surface  240 A of FM shield  195 A is textured. The term textured is defined to include roughing, lining and stippling. Otherwise FM shields  195  and  195 A are identical. Texturing is optional, however, texturing lowers the possibility of layers of foreign material that deposit on surface  240 A will shed, peel or flake off. Texturing may be accomplished, for example, by sand blasting, bead blasting or vapor blasting. Texture may be accomplished by grinding, scratching or machining surface  240 A. All variations of FM shields discussed infra and illustrated in  FIGS. 4B ,  5 B,  6 B,  7 B  8 B and  9 B may have textured inside surfaces. 
     FIG. 4A  is a top view and  FIG. 4B  is a side view through line  4 B— 4 B of  FIG. 4A  of a second FM shield according to the present invention. In  FIGS. 4A and 4B , an FM shield  195 B is similar to FM shield  195  of  FIGS. 3A and 3B  except an integral dual tapered ring portion  305  is integrally formed to top portion  295 . Ring portion  305  has an outer sloped surface  310  and an inner sloped surface  315  (both of equal length and both slanting at an angle w from an axis  320  aligned parallel with ion beam axis  205 ) and meeting in a edge  325 . FM shield  195 B has a top circular opening  325 A defined by edge  325  and bottom circular opening  230 A defined by bottom surface  230 . Ring portion  305  has a height H 5 . Continuing the example of  FIGS. 3A and 3B , H 5  is about 1.25 inches and ω is about 10°. The 10° taper on outer and inner surfaces  310  and  315  allows in increase in overall effective height from H 1  to H 1  plus H 5  without effecting the maximum values of α and β (see  FIG. 1B ). 
     FIG. 5A  is a top view and  FIG. 5B  is a side view through line  5 B— 5 B of  FIG. 5A  of a third FM shield according to the present invention. In  FIGS. 5A and 5B , an FM shield  195 C is similar to FM shield  195  of  FIGS. 3A ,  3 B and  3 C except there is an additional hollow cylindrical portion and an additional hollow tapered transition portion. In  FIGS. 5A and 5B , a bottom hollow cylindrical portion  330  having an outside diameter D 1  is joined to a middle hollow cylindrical portion  335  having an outside diameter D 3  by a first hollow tapered transition portion  340 . Middle hollow cylindrical portion  335  is joined to a top hollow cylindrical portion  345  having an outside diameter D 4  by a second hollow tapered transition portion  350 . Top hollow cylindrical portion  345  has a flat top edge  355 . Portions  330 ,  335 ,  340 ,  345  and  350  of FM shield  195 C are integrally formed. FM shield  195 C has a top circular opening  355 A defined by top surface  355  and a bottom circular opening  360 A defined by a bottom surface  360 . FM shield  195 C has an overall height H 6 . D 1  is greater than D 3  and D 3  is greater than D 4 . When FM shield  195 C is installed in ion beam system  100  (see  FIG. 1A ) the center of diameters D 1 , D 4  and D 4  are intersected by ion beam axis  205 . 
   FM shields of the type illustrated in  FIGS. 5A and 5B  and described supra, may include any number of hollow cylinder portions and hollow tapered transition portions. 
     FIG. 6A  is a top view and  FIG. 6B  is a side view through line  6 B— 6 B of  FIG. 6A  of a fourth FM shield according to the present invention. In  FIGS. 6A and 6B , an FM shield  195 D is similar to FM shield  19 C of  FIGS. 5A and 5B  except an integral dual tapered ring portion  365  is integrally formed to top portion  345 . Ring portion  365  has an outer sloped surface  370  and an inner sloped surface  375  (both of equal length and both slanting at an angle w from an axis  380  aligned with ion beam axis  205 ) and meeting in a edge  385 . FM shield  195 D has a top circular opening  385 A defined by edge  385  and a bottom circular opening  360 A defined by bottom surface  360 . Ring portion  360  has a height H 7 . ω is about 10°. The 10° taper on outer and inner surfaces  370  and  375  allows in increase in overall effective height from H 6  to H 6  plus H 7  without effecting the maximum values of α and β (see  FIG. 1B ). 
     FIG. 7A  is a top view and  FIG. 7B  is a side view through line  7 B— 7 B of  FIG. 7A  of a fifth FM shield according to the present invention. In  FIGS. 7A and 7B , FM shield  195 E comprises a hollow truncated conical portion  390  having a top surface  395  and a bottom integral ring portion  400  having a bottom surface  405 . Multiple rows (two are illustrated) of optional slots  410  are formed in wall  410  of conical portion  405 . FM shield  195 E has a top circular opening  395 A defined by top surface  395  and a bottom circular opening  405 A defined by bottom surface  405 . FM shield has a bottom outside diameter of D 1 , a top outside diameter of D 5  and a height of H 8 . When FM shield  195 E is installed in ion beam system  100  (see  FIG. 1A ) the center of diameters D 1  and D 5  are intersected by ion beam axis  205 . 
     FIG. 8A  is a top view and  FIG. 8B  is a side view through line  8 B— 8 B of  FIG. 8A  of a sixth FM shield according to the present invention. In  FIGS. 8A and 8B , FM shield  195 F comprises a hollow cylinder  420  having a bottom surface  425  and a top surface  430 . FM shield  195 F has a top circular opening  430 A defined by top surface  430  and a bottom circular opening  425 A defined by bottom surface  425 . FM shield has diameter of D 1  and a height of H 9 . When FM shield  195 F is installed in ion beam system  100  (see  FIG. 1A ) the center of diameter D 1  is intersected by ion beam axis  205 . 
     FIG. 9A  is a top view and  FIG. 9B  is a side view through line  9 B— 9 B of  FIG. 9A  of a seventh FM shield according to the present invention. In  FIGS. 9A and 9B , an FM shield  195 G is similar to FM shield  195 F of  FIGS. 8A and 8B  except an integral dual tapered ring portion  435  is integrally formed with cylinder  420 . Ring portion  435  has an outer sloped surface  440  and an inner sloped surface  445  (both of equal length and both slanting at an angle ω from an axis  450  aligned with ion beam axis  205 ) and meeting in a edge  455 . FM shield  195 G has a top circular opening  445 A defined by edge  455  and bottom circular opening  425 A defined by bottom surface  425 . Ring portion  435  has a height H 10 . ω is about 10°. The 10° taper on outer and inner surfaces  440  and  445  allows in increase in overall effective height from H 9  to H 9  plus H 10  without effecting the maximum values of α and β (see  FIG. 1B ). 
     FIG. 10  is detailed cross-sectional view of a bellows area of an ion beam tool according to a second embodiment of the present invention.  FIG. 10  is similar to  FIG. 2 , except an upper FM shield  460  has been added. Upper FM shield  460  includes a collar  460  attached to outer surface  250  of electron shower tube  170  and positioned between vacuum chamber  185  and FM shield  195  and a flange  470 . Flange  470  extends outward and downward from vacuum chamber  185  toward FM shield  195 . Optionally flange  470  may extend outwardly only. Flange  470  extends past top surface  235  of FM shield  470 . A space is left between upper FM shield  460  and FM shield  195  sufficient large enough so as to not effect the pumping efficiency of the tool. Suitable materials for upper FM shield  460  include but is not limited to aluminum, stainless steel, ceramics (examples of which include boron nitride, aluminum oxide, aluminum silicate), silicon carbide, carbon, silicon and high temperature polymers. Upper FM shield may be used with any of FM shields  195 A,  195 B,  195 C,  195 D,  195 E,  1955 F and  195 G described supra. 
   Thus, the present invention reduces foreign material contamination of substrates in ion beam systems. 
   The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.