Abstract:
A carrier capable of holding one or more workpieces is disclosed. The carrier includes movable projections located along the sides of each cell in the carrier. This carrier, in conjunction with a separate alignment apparatus, aligns each workpiece within its respective cell against several alignment pins, using a multiple step alignment process to guarantee proper positioning of the workpiece in the cell. First, the workpieces are moved toward one side of the cell. Once the workpieces have been aligned against this side, the workpieces are then moved toward an adjacent orthogonal side such that the workpieces are aligned to two sides of the cell. Once aligned, the workpiece is held in place by the projections located along each side of each cell. In addition, the alignment pins are also used to align the associated mask, thereby guaranteeing that the mask is properly aligned to the workpiece.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This Invention was made with U.S. Government support under Contract No. DE-EE0004737 awarded by the Department of Energy. The Government has certain rights in this invention. 
    
    
     BACKGROUND 
     Workpiece processing, such as solar cell or semiconductor wafer processing, requires a plurality of steps to achieve the finished product. In some embodiments, the workpiece must be moved from a station which performs one of these steps to another station which performs a different step. In some cases, the workpiece is placed in a carrier, which holds and protects the workpiece during these transitions. 
     However, these carriers are often constructed such that they hold or envelop the edges of the workpieces, thereby covering at least a portion of the workpiece. As a consequence, in some cases, the workpiece typically must be removed from the carrier to be processed, adding time and complexity to the process. In those cases where processing is performed on the workpiece while in the carrier, additional steps are often required to insure that the edges, which were blocked or obscured by the carrier, receive the same treatments as the remainder of the workpiece. Again, these extra steps add time and complexity to the process. Furthermore, in some cases, the edges of the workpiece that are covered during the processing may not be treated in another process step, reducing the efficiency or performance of the workpiece. 
     Additionally, during workpiece processing, it is often necessary to place a mask in front or on top of the workpiece to limit the exposure of the workpiece to energy, typically in the form of ions or light. This mask must be precisely aligned to the workpiece to insure that the workpiece is properly processed. Unfortunately, this critical alignment may be compromised by various forms of errors, such as thermal expansion of the mask or other materials that are not thermally matched with regard to the coefficient of thermal expansion (CTE) during processing, misalignment of the mask to the workpiece, general tolerance stack ups, workpiece irregularities, and other issues. 
     Therefore, it would be beneficial if there were a carrier that could be used to hold a workpiece, such that the carrier did not block or obscure the edges of the workpiece, thereby allowing complete processing of the workpiece while in the carrier. Furthermore, it would be beneficial if this carrier facilitated the alignment of a mask to the workpiece. Still further, it would be advantageous if this carrier were able to hold a plurality of workpieces and a plurality of masks, each associated with one of the workpieces. 
     SUMMARY 
     A carrier capable of holding a plurality of workpieces is disclosed. The carrier is divided into a plurality of bounded regions, called cells, which each hold one workpiece. The carrier includes movable projections located along the sides of each cell. This carrier, in conjunction with a separate alignment apparatus, aligns each workpiece within its respective cell against several alignment pins, using a multiple step alignment process to guarantee proper positioning of the workpiece in the cell. First, the workpieces are moved toward one side of the cell. Once the workpieces have been aligned against this side, the workpieces are then moved toward an adjacent orthogonal side such that the workpieces are aligned to two sides of the cell. Once aligned, the workpiece is held in place by the projections located along each side of each cell, which press against the edges of the workpiece. These projections hold the workpiece without obscuring the edges, the top surface or the bottom surface of the workpiece that is to be processed. In addition, the alignment pins, to which the workpiece is aligned, are also used to align the associated mask, thereby guaranteeing that the mask is properly aligned to the workpiece. 
     The alignment apparatus includes a first set of actuators that cause the carrier to move each of the workpieces toward a side of the cell. The alignment apparatus also includes a second set of actuators, operative after the first set of actuators, which cause the carrier to align the workpieces toward a second adjacent orthogonal side of the cell. The alignment apparatus may also include another set of actuators which can be used to lift and lower the workpieces to the carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a perspective view of a carrier according to one embodiment; 
         FIG. 2  shows an enlarged view of a mask to be used with the carrier of  FIG. 1 ; 
         FIG. 3  shows a detail of one of the mask alignment features located on a mask that can be installed in a cell of the carrier; 
         FIG. 4  shows an enlarged view of one cell of the carrier with the mask removed; 
         FIG. 5  shows an enlarged view of the cell alignment pin engaged with the mask alignment feature; 
         FIG. 6  shows a workpiece after alignment; 
         FIG. 7  shows a workpiece in a cell prior to alignment; 
         FIG. 8  shows a workpiece during the alignment process; 
         FIG. 9  is an enlarged view of the movable projection according to one embodiment; 
         FIGS. 10A-C  show the interaction between the actuator and the movable projection; 
         FIG. 11  shows an alignment apparatus that can be used with the carrier of  FIG. 1 ; and 
         FIG. 12A-C  show the alignment apparatus of  FIG. 11  during various stages of execution. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows one embodiment of the carrier  100 . This embodiment shows  16  cells  110 , grouped as a 4×4 matrix. However, other configurations and cell quantities are within the scope of the invention. The carrier  100  includes four outer walls  120   a - d  and a plurality of inner walls  125 . These outer walls and inner walls are arranged in a grid pattern, where the area between intersecting walls defines a cell  110 . The number of inner walls  125  helps determine the number of cells  110  in the carrier  100 . Of course, if only one cell  110  is required, no inner walls  125  are needed. 
     The upper surface of the outer walls  120   a - d  and inner walls  125 , also referred to as cladding, is preferably constructed of graphite to minimize contamination caused by sputtering. The interior frame of the carrier  100 , the components within the interior frame, and any surfaces that are not exposed to ion implantation may be constructed of a different material, such as aluminum.  FIG. 1  also shows a mask  130  positioned on one of the cells  110 . 
       FIG. 2  is an enlarged view of the mask  130  shown in  FIG. 1 . The mask  130  includes shoulders  140   a - e , which rest atop the outer walls  120   a ,  120   d  and the inner walls  125  (see  FIG. 1 ). In some embodiments, the mask  130  is a monolithic graphite machined component. Located on several of the shoulders  140   a ,  140   d ,  140   e  are mask locating features  145 . These mask locating features  145  may be constructed of silicon carbide and pressed into corresponding holes located in the shoulders  140   a ,  140   d ,  140   e  of the mask  130 . These mask locating features  145  are machined based on the master module layout datums in order to insure that each mask  130  accurately and repeatedly aligns to each cell  110  even during elevated heat environments. 
       FIG. 3  shows a bottom view of the mask  130  of  FIG. 2 . This figure is enlarged so that the lower surface of shoulder  140   d  can be seen. Designed into this shoulder  140   d  is one or more elongated depressions  150 , or V-grooves. The bottom of a mask locating feature  145  is visible and is located within a respective elongated depression  150  or V-groove. The alignment pins (see  FIG. 4 ) fit into these elongated depressions  150  and align to the mask locating features  145 . Other shoulders  140  may also have one or more elongated grooves and mask locating features. 
       FIG. 4  shows an enlarged view of a cell  110  without a mask  130  installed. Portions of outer walls  120   a,b  and inner walls  125   a,b  form the perimeter of cell  110 . Located at the bottom surface of the cell  110  within the perimeter of the cell  110  is a platen  160 . The platen  160  may be an electrostatic chuck, as is known in the art. The platen  160  may have one or more openings  165  in it, which allow a set of lift pins to extend through the platen  160  to lift the workpiece, as described in more detail below. 
     Along the outer edges of the platen  160  (i.e. those portions nearest to the perimeter) may be shielding  170 , which insures that the platen  160  is not exposed to the ions during implantation. This may occur if the area occupied by the workpiece is slightly smaller than the area defined by the perimeter of cell  110 . This shielding  170  may be graphite to lower the risk of contamination. Located along inner wall  125   b  are two alignment pins  180   a,b . A third alignment pin  180   c  is located along outer wall  120   a . These three pins  180   a - c  are located on the perimeter and serve to align the workpiece within the cell  110 . These pins also serve to align the mask  130 , via the mask locating features  145  illustrated in  FIGS. 2-3  that mate with these alignment pins  180   a - c . While three alignment pins  180   a - c  are shown, a different number of alignment pins may be used. For example, two alignment pins may be located along outer wall  120   a.    
       FIG. 5  shows an enlarged view of the alignment pin  180  engaged with shoulder  140  of the mask  130 . The mask  130  is shown as transparent so the interaction between the mask  130  and the alignment pin  180  can be shown. The mask locating feature  145  is disposed within the elongated depression  150 , as described above. When the mask is engaged with the carrier  100 , the alignment pin  180  is positioned within the mask locating feature  145 . 
       FIG. 6  shows an enlarged view of a cell  110  with the graphite cladding removed to allow visibility into the internal components of the carrier  100 . Located under the graphite cladding are the mechanisms used to align the workpiece  10  to the alignment pins  180   a - c  of the cell  110 . Located along each side of the cell  110  are one or more movable projections  190 , which operate to move the workpiece  10  when actuated. The movable projections  190  may be any suitable device, such as pegs or wheels. These movable projections  190  are each naturally biased through the use of a biasing member, such as a spring, elastic band, or the like.  FIG. 6  shows two such movable projections  190  located on each side of the cell  110 . In one embodiment, movable projections  190   a,b  are inwardly biased, so as to move the projections toward the interior of cell  110 . Similarly, movable projections  190   c,d  are also inwardly biased. In contrast, the remaining movable projections  190   e - h  are all outwardly biased, so that they move away from the cell  110 . The terms “inward” and “outward” are referenced to the interior of the cell of interest. Movable projections  190  located on opposite sides of the perimeter are biased in the opposite way. In some embodiments, the movable projections  190  located along those sides on which the alignment pins  180  are disposed are naturally outwardly biased, while the remaining movable projections  190  are naturally inwardly biased. Of course, other biasing configurations are possible. 
     While movable projections  190  are shown along each side of the perimeter of the cell  110 , other embodiments are possible. For example, in some embodiments, movable projections  190  are only located on those sides opposite the sides where the alignment pins  180  are disposed. 
     In some embodiments, such as that shown in  FIG. 6 , the movable projections  190  located along the inner walls  125 , such as movable projections  190   a - d  may be used for two adjacent cells  110 . In other words, movable projections  190   a - d  would also serve as movable projections for an adjacent cell. In other embodiments, each cell  110  may have dedicated movable projections  190 . 
     In operation, as shown in  FIG. 7 , to place the workpiece  10  in the carrier  100 , the movable projections  190  are all actuated so as to overcome their natural biased position. In other words, movable projections  190   a - d  are outwardly biased, while movable projections  190   e - h  are inwardly biased. This allows the workpiece to be placed on the platen  160 . Note that movable projections  190   a,b  are outwardly biased with respect to cell  110 , but would be inwardly biased relative to an adjacent cell  110 . Thus, these movable projections can be operative in two adjacent cells  110 . In this position, the workpiece  10  is not being pressed toward the alignment pins  180 . 
     As seen in  FIG. 8 , movable projections  190   a,b  are then allowed to return to their naturally biased position, causing them to extend inside the perimeter of the cell  110 . This action pushes the workpiece  10  toward the alignment pins  180   a,b . Once the workpiece  10  contacts the alignment pins  180   a,b , its movement in this direction ceases. The natural bias of the movable projections  190   a,b  holds the workpiece  10  against the alignment pins  180   a,b.    
     As seen in  FIG. 6 , after movable projections  190   a,b  have ceased movement, movable projections  190   c,d  are allowed to return to their naturally biased position. This serves to push the workpiece  10 , which is already aligned to alignment pins  180   a,b  toward alignment pin  180   c . Once the workpiece  10  contacts the alignment pin  180   c , its movement in this direction ceases. The natural bias of the movable projections  190   c,d  hold the workpiece  10  against the alignment pin  180   c . In this way, the workpiece  10  is held in place without blocking or obscuring any portion of the workpiece  10 . 
     To remove the workpiece  10  from the carrier  100 , these steps may be executed in reverse order. In this case, movable projections  190   c,d  are actuated to overcome their natural biased positions, and movable projections  190   g,h  move the workpiece  10  away from alignment pin  180   c . Subsequently, movable projections  190   a,b  are actuated to overcome their natural biased positions, and movable projections  190   e,f  move the workpiece  10  away from alignment pins  180   a,b.    
     Although this disclosure describes a sequential operation where the workpiece  10  is first moved toward alignment pins  180   a,b , and then toward alignment pin  180   c , other embodiments are possible. For example, the workpiece  10  can be moved in both directions simultaneously. In another embodiment, the workpiece  10  is moved toward alignment pin  180   c  first, and then toward alignment pins  180   a,b.    
     Similarly, the process of releasing the workpiece  10  may be different. In another embodiment, movable projections  190   a - d  are actuated simultaneously, so that workpiece moves away from all alignment pins  180   a - c  simultaneously. In another embodiment, movable projections  190   a,b  are actuated first, thereby pushing the workpiece  10  away from alignment pins  180   a,b . The movable projections  190   c,d  are then actuated, moving the workpiece  10  away from alignment pin  180   c.    
     In other words, the movable projections  190  can be actuated in any predetermined sequence. 
     The movable projections  190  can be actuated in a variety of ways.  FIG. 9  shows an enlarged view of one embodiment of a movable projection  190 . The movable projection  190  includes a rotatable wheel  191 , which is pivotable about an axis located near one end of projection  190 . The movable projection  190  is pivotable about a point  192 . The opposite end of the projection  190  is attachable to a biasing member  193 . The biasing member  193  causes the movable projection  190  to rotate about the point  192 . The biasing member  193  may be a compliant spring mechanism that allows for irregularly shaped workpieces  10  to be used in the carrier  100 . It also allows for expansion caused by thermal growth during processing, since the energy imparted on the workpiece  10 , such as during implantation, may be significant and may cause parts of the workpiece  10  to grow at different rates. Biasing members  193  are also independent on each movable projection  190  allowing each one to be used independently. This may reduce hertzian stresses on the edge of each workpiece  10 . Actuator  221  is the mechanical device that pushes up and down and causes movable projection  190  to pivot about point  192 . Biasing member  193  then serves as the counteracting mechanism, allowing the movable projection  190  to return to a naturally biased position after actuator  221  is retracted from the opening  194 . A spring stop that help capture the biasing member  193  may be located on the back side of biasing member  193 . In some embodiments, the biasing member  193  can push the movable projection  190 , while in other embodiments, the biasing member  193  pulls the movable projection  190 . In one position, the movable projection  190 , and specifically the wheel  191 , extends into the cell  110 . In the second position, the wheel  191  is retracted from the cell  110 . Located in the movable projection  190  is an opening  194 . This opening  194  is aligned to an aperture under the movable projection  190 , through which an actuator may extend. When the actuator extends into this opening  194 , it moves the movable projection  190  and holds it in a help position, different than its naturally biased position. 
     While  FIG. 9  shows a wheel  191 , other configurations of the movable projection  190  are also within the scope of the disclosure. For example, the wheel  191  may be replaced with a peg or other rigid member that does not need to rotate which performs the same function. This peg or other mechanism may still be connected to the biasing member  193 . The surface of the wheel  191 , peg, or other mechanism that contacts the workpiece  10  may be flat, angled, curved, or other shapes. 
       FIGS. 10A-C  shows a cross-sectional view of the movable projection  190 , showing the interaction between the actuator  221  and the opening  194 . As can be seen in  FIG. 10A , the actuator  221  is not exactly aligned to the opening  194  when the moveable projection  190  is in its naturally biased position. The opening  194  in the movable projection  190  has a sidewall having a downward facing ramp  195 . As the actuator  221  moves upward through an aperture in the carrier  100 , it travels along this ramp  195 , causing the movable projection  190  to move away from its natural biased position, as seen in  FIG. 10B . When the actuator  221  is fully extended, as shown in  FIG. 10C , the movable projection  190  is in the held position. 
       FIG. 11  shows one possible alignment apparatus  200 . This apparatus  200  can be used to lower the workpiece  10  onto the carrier  100 , actuate the movable projections  190  in a predetermined sequence, and later, lift the workpiece from the carrier  100 . 
     The apparatus  200  has a number of plates, some of which are stationary and others of which are movable. The top plate  210  is stationary and provides a platform on which the carrier  100  may be disposed. This top plate  210  may have a plurality of holes through which lift pins  231  and actuators  221  may pass. In other embodiments, a portion of the top plate  210 , such as the middle portion, may be removed to allow a space where these lift pins  231  and actuators  221  may pass. The top plate  210  may also have a mechanism used to hold or secure the carrier  100  to the top plate  210 . In one embodiment, this mechanism may be a set of magnets, which are aligned to magnetic portions located on the bottom of the carrier  100 . 
     Positioned beneath the top plate  210  is a movable plate, known as the actuator plate  220 . The actuator plate  220  is coupled to a linear actuator  280 , which moves the actuator plate  220  up and down along the central shaft  290 . Located on the upper surface of the actuator plate  220  and extending upwardly, is a plurality of actuators  221 . These actuators  221  may be of various heights. In the case of two different heights, one set of actuators  221   a  are used to actuate the movable projections  190   a,b  and  190   e,f  of each cell  110  (see  FIG. 6 ). These actuators are of a first height. A second set of actuators  221   b  are used to actuate the movable projections  190   c,d  and  190   g,h  of each cell  110 . These actuators  221   b  are of a second height, which is greater than the first height. These actuators  221  pass through openings in the top plate  210 , as described above. Other various height actuators may be employed to facilitate moving the workpiece to specific load, unload, clamp, offset, and rotational positions. This may be performed for processing, tailoring improvements, imaging for repeatability and accuracy verification, or teaching methods for robots, for example. 
     Beneath the actuator plate  220  is the lift plate  230 . The top surface of the lift plate  230  has a plurality of upwardly extending lift pins  231 , which are used to lift the workpieces  10  from the carrier  100 . These lift pins  231  are located so as to contact the underside of the workpieces  10 . As described above, each of the platens  160  (located in carrier  100 ) may have openings to allow these lift pins  231  to extend into the carrier  100  and lift the workpieces  10 . This lift plate  230  is controlled by a linear actuator  281 , which allows the lift plate  230  to move vertically along the central shaft  290 . To accommodate these lift pins  231 , actuator plate  220  may have openings therein to allow the lift pins  231  to pass through. 
     The alignment apparatus  200  may also have a lower plate  240 , which is stationary and used for bearing and as support anchors. 
     In operation, as shown in  FIG. 12A , the lift plate  230  is lifted toward the top plate  210 , as is the actuator plate  220 . The lift pins  231  extend through the carrier  100 . A robot or other mechanism then loads a workpiece  10  on the set of lift pins  231  associated with each respective cell  110 . In some embodiments, there are four lift pins  231  associated with each cell  110 , although other numbers of lift pins  231  can extend through each cell. 
     The lift plate  230  then descends as controlled by linear actuator  281 , which allows the workpieces  10  to sit in their respective cells  110 , as shown in  FIG. 12B . In this view, the workpieces  10  are no longer visible, as they are sitting within the carrier  100 . At this time, the actuator plate  220  is still positioned up toward the top plate  210 , such that the actuators  221   a,b  are engaged with openings  194  in the movable projections  190 , as shown in  FIG. 10C . 
     As the actuator plate  220  is moved downward, as seen in  FIG. 12C , away from the top plate  210  and the carrier  100 , the first set of actuators  221   a , which contain shorter pins, disengages from the movable projections  190   a,b  and  190   e,f  (see  FIGS. 6-8 ) first. This allows these projections  190   a,b  and  190   e,f  to move to their natural biased positions and moves the workpiece  10  against the alignment pins  180   a,b , as shown in  FIG. 8 . 
     As the actuator plate  220  continues to move away from the top plate  210 , as seen in  FIG. 12C , the second set of actuators  221   b , which are longer, disengages from the remaining movable projections  190   c,d  and  190   g,h . This allows the remaining movable projections  190   c,d  and  190   g,h  to return to their naturally biased positions. This movement causes the workpiece  10  to be moved against the alignment pin  180   c  (see  FIG. 6 ). The time between the disengagement of the first set of actuators  221   a  and the second set of actuators  221   b  is determined based on the difference in height between these two sets of actuators  221   a,b  and the speed at which the actuator plate  220  moves (assuming that the actuator plate  220  moves at a constant speed). Of course, this time can be adjusted by using a non-linear speed profile for the actuator plate  220 . This can be achieved by controlling the linear actuator  280  to slow the speed of the actuator plate  220  after the first set of actuators  221   a  have disengaged. 
     Performing two direction alignment in two separate steps may, in some embodiments, reduce workpiece breakage or workpiece jamming or misalignment in the cell. In other embodiments, the alignment in both directions is performed simultaneously. 
     In another embodiment, the actuator plate  220  can be implemented as two separate plates, where one plate has the first set of actuators  221   a  and the second plate has the second set of actuators  221   b . These plates may be independently controlled by separate linear actuators, so that the actuators  221  can be moved in any desired sequence. This configuration allows different engagement and disengagement sequences. 
     As mentioned above, other embodiments are possible. For example, all actuators  221  may be the same height, since the alignment of the workpiece  10  occurs in both directions simultaneously. 
     Once the actuator plate  220  and lift plate  230  have been lowered, the workpieces are all aligned and clamped via the movable projections  190  (see  FIG. 9 ) to their respective cells. Once the workpieces are clamped, the carrier  100  may be processed. The processing of the workpieces may include ion implantation, deposition, etching, or other processing steps, as are well known in the art. In one embodiment, masks, such as those shown in  FIGS. 1-3 , are placed on each respective cell prior to the processing of the workpieces. This may be done using a robotic mechanism. In another embodiment, no mask is used during the processing. The carrier  100  may be moved to a different location for processing, such as ion implantation, than where the workpiece alignment occurs. This processing may involve flipping or rotating the carrier  100 . The embodiments disclosed herein may retain the workpieces  10  in the cells  110  during this moving, flipping, rotating, or other motion. 
     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. Furthermore, 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. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.