Patent Publication Number: US-2012043712-A1

Title: Mechanism and method for aligning a workpiece to a shadow mask

Description:
FIELD 
     This disclosure relates to a method and mechanism for aligning workpieces to a shadow mask, such as for use in an ion implantation process. 
     BACKGROUND  
     An electronic device may be created from a workpieces that has undergone various processes. One of these processes may include introducing impurities or dopants to alter the electrical properties of the original workpiece. For example, charged ions, as impurities or dopants, may be introduced to a workpiece, such as a silicon wafer, to alter electrical properties of the workpiece. One of the processes that introduces impurities to the workpiece may be an ion implantation process. 
     An ion implanter is used to perform ion implantation or other modifications of a workpiece. A block diagram of a conventional ion implanter is shown in  FIG. 1 . Of course, many different ion implanters may be used. The conventional ion implanter may comprise an ion source  102  that may be biased by a power supply  101 . The system may be controlled by controller  120 . The operator communicates with the controller  120  via user interface system  122 . The ion source  102  is typically contained in a vacuum chamber known as a source housing (not shown). The ion implanter system  100  may also comprise a series of beam-line components through which ions  10  pass. The series of beam-line components may include, for example, extraction electrodes  104 , a 90° magnet analyzer  106 , a first deceleration (D 1 ) stage  108 , a 70° magnet collimator  110 , and a second deceleration (D 2 ) stage  112 . Much like a series of optical lenses that manipulate a light beam, the beam-line components can manipulate and focus the ion beam  10  before steering it towards a workpiece or wafer  114 , which is disposed on a workpiece support  116 . 
     In operation, a workpiece handling robot (not shown) disposes the workpiece  114  on the workpiece support  116  that can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat” (not shown). Meanwhile, ions are generated in the ion source  102  and extracted by the extraction electrodes  104 . The extracted ions  10  travel in a beam-like state along the beam-line components and implanted on the workpiece  114 . After implanting ions is completed, the workpiece handling robot may remove the workpiece  114  from the workpiece support  116  and from the ion implanter  100 . 
     Referring to  FIG. 2 , there is shown a block diagram illustrating one embodiment of a workpiece support  116  used to support the workpiece  114  during the ion implantation process. In this embodiment, the workpiece  114  is mounted on a platen  175 , such as by electrostatic force. The platen  175  is rotatably connected to structure  185 . In some embodiments, the platen  175  is hinged to structure  185  such that the platen  175  and workpiece  114  may pivot along path  183 . For clarity, the axis about which the platen  175  rotates is referred to as the x-tilt axis, and allows the workpiece to be tilted to allow angled implants. In some embodiments, the structure  185  is also able to rotate about a second axis  182 , known as the y-axis tilt axis. Using rotation about these two axes, it is possible to place the workpiece  114  at any desired angle relative to the ion beam  10 . In some embodiments, the structure  185  may also be able to move up and down, such as parallel to second axis  182 , in order to perform scanned implants. 
     In some embodiments, it is desirable to place a shadow mask in front of the workpiece  114  to perform a patterned implant. This shadow mask must be aligned with the workpiece, in one direction or in both the x and y directions, such that the mask is properly positioned. In some embodiments, the mask is aligned to the workpiece. In other embodiments, the shadow mask is roughly aligned to the platen, and the workpiece is then precisely aligned with the shadow mask.  FIG. 3  shows a shadow mask  195  and a workpiece  114 . Alignment features  197  are positioned on the side of workpiece  114  to help align the shadow mask  195  with the workpiece  114 . Similarly, alignment features  198  are positioned on the bottom side of the workpiece  114  to help alignment with the shadow mask  195  in that direction. In this embodiment, the shadow mask  195  is assumed to be fixed, while the workpiece  114  can be moved relative to the shadow mask  195  and the alignment features  197 ,  198 . However, in other embodiments, the workpiece  114  is kept in a fixed position and the shadow mask  195  is moved relative to the workpiece  114 . 
     It would be beneficial if the shadow mask  195  could be easily aligned with the workpiece  114 . Referring back to  FIG. 2 , it can be seen that the workpiece  114  can be aligned with the shadow mask  195  using alignment features  198 , by tilting the platen  175  along path  183 , such that gravity aids in moving the workpiece  114  downward toward the alignment features  198 . However, gravity cannot be used to perform alignment in the orthogonal direction, as the workpiece support  116  does not rotate such that gravity can assist in the alignment with features  197 . Therefore, more complex, and potentially manual, alignment is required to properly align a workpiece and a shadow mask with prior art workpiece supports. 
     Therefore, it would be beneficial if there were a mechanism and method for aligning a workpiece and a shadow mask with minimal intervention. It would be further advantageous if such a mechanism and method relied on gravity to perform the alignment of these components to minimize manual interaction and cost. 
     SUMMARY 
     The problems of the prior art are overcome by the mechanism and method of this disclosure. A workpiece support is defined whereby the platen, and thus the workpiece, can be tilted about at least two axes, which allows gravity to align the workpiece with a shadow mask in two orthogonal directions. In some embodiments, the workpiece support utilizes an axis of rotation that is orthogonal to the surface of the workpiece, in conjunction with a second axis that is parallel to the surface of the workpiece. Additionally, a method of aligning the workpiece using this workpiece support is also disclosed. Further, the workpiece support can be utilized to remove the workpiece from the support after implantation is completed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only. 
         FIG. 1  represents a traditional ion implantation system; 
         FIG. 2  represents a block diagram showing a workpiece support; 
         FIG. 3  represents a workpiece support having features for aligning a shadow mask and a workpiece; 
         FIG. 4  represents three dimensions relative to a workpiece; 
         FIG. 5  represents a workpiece support according to one embodiment; 
         FIG. 6  represents the workpiece support of  FIG. 5  rotated above the y-tilt axis; 
         FIG. 7  is an exaggerated view of the workpiece and shadow mask shown in  FIG. 6 ; 
         FIG. 8  represents the workpiece support of  FIG. 5  rotated above the x-tilt axis; 
         FIG. 9  represents the workpiece support of  FIG. 5  rotated about both the x-tilt and y-tilt axes; and 
         FIG. 10  represents the workpiece support of  FIG. 5  vertically oriented to allow implantation. 
     
    
    
     DETAILED DESCRIPTION 
     In the present disclosure, several embodiments of an apparatus and a method for aligning a workpiece and a shadow mask are introduced. For purpose of clarity and simplicity, the present disclosure will focus on an apparatus and a method for aligning a workpiece that is processed by a beam-line ion implanter. Those skilled in the art, however, may recognize that the present disclosure is equally applicable to other types of processing systems including, for example, a plasma immersion ion implantation (“PIII”) system, a plasma doping (“PLAD”) system, an etching system, an optical based processing system, and a chemical vapor deposition (CVD) system. As such, the present disclosure is not to be limited in scope by the specific embodiments described herein. 
     As described above in  FIGS. 2 and 3 , current workpiece supports allow the workpiece to be rotated in two directions. Typically, when the workpiece support is rotatable in two directions, one axis is the major axis, while the other is the minor or subordinate axis. In other words, rotation about one axis (the minor axis) does not affect the orientation of the major axis. Looking at  FIG. 2 , note that rotation about the x-tilt axis (i.e. movement along path  183 ) does not affect the orientation of the second axis  182 . However, movement about the second, or vertical, axis  182  changes the orientation of the x-tilt axis. As shown in  FIG. 2 , the x-tilt axis is orthogonal to the surface of the page. However, if there were a quarter)(90°) turn about the second, or vertical, axis  182 , the x-tilt axis would be parallel to the surface of the page. Thus, in this embodiment, the second, or vertical, axis  182  is the major axis. Because of this, gravity-based alignment is only possible in one dimension. As stated above, the workpiece support  116  of  FIG. 2  allows gravity-based alignment with respect to features  198  (See  FIG. 3 ). However, the workpiece support  116  cannot be rotated such that gravity can be used to align the workpiece  114  with features  197  (See  FIG. 3 ). 
     Thus, to allow alignment of the workpiece in two dimensions, the major axis is preferably not in the vertical direction.  FIG. 4  shows a workpiece  200 , having three defined axis. The x axis  205  and y axis  210  are both along the plane of the workpiece surface and are orthogonal to one another. The z axis  215  is orthogonal to the surface of the workpiece  200 . To maximize the flexibility of various implantation angles and techniques, another desired feature is that the workpiece  200  can preferably be tilted about both axis  205 ,  210  that are parallel to its surface. This allows the workpiece  200  to be oriented in any position relative to the ion beam. 
       FIG. 5  shows a first embodiment of a workpiece support that meets these requirements. The workpiece support  300  includes a platen  310 , which is rotatably mounted on the distal ends of two extending arms  315 ,  317 . In some embodiments, the arms  315 ,  317  are at least as long as the radius of the platen  310 , so that the platen can freely rotate about the y-tilt axis  318 . In other embodiments, the arms need not be as long as the radius, as the platen may have a limited range of motion. The mask  320  and workpiece  330  are placed on the top surface of the platen  310 . As is done in the prior art, electrostatic force can be used to hold the workpiece  330  in place on the platen  310 . The extending arms  315 ,  317  are connected at their proximate end to a rotatable disk  340 . In some embodiments, the rotating disk  340  and the extending arms  315 ,  317  are of unitary construction. Rotatable disk  340  rotates about x-tilt axis  345 . Preferably the y-tilt axis  318  and the x-tilt axis  345  are co-planar, such that the x-tilt axis  345  passes through the y-tilt axis  318 , as shown in  FIG. 5 . 
       FIG. 5  shows the platen oriented such that the workpiece  330  is horizontal. Note that ion beam  350  is emanating from a source (not shown) positioned to the right, relative to the workpiece support  300 .  FIG. 6  shows the platen  310  rotated downward due to rotation about the y-tilt axis  318 .  FIG. 7  shows an expanded view of the workpiece  300  in this rotated position. Note that alignment features  360 ,  361  exist which are used to align the workpiece  330  to the shadow mask  320  in the x and y dimensions, respectively. When the platen  310  is rotated about the y-tilt axis  318 , gravity-assisted alignment can be used with respect to alignment features  361 . 
     Returning to  FIG. 5 , the platen  310  can also be rotated about the x-tilt axis  345 .  FIG. 8  shows the platen  310  and workpiece  330  rotated about the x-tilt axis  345 . In this orientation, gravity assisted alignment can be performed with respect to alignment features  360  (See  FIG. 7 ). 
     Thus, by rotating the workpiece about both the y-tilt axis  318  and the x-tilt axis  345 , it is possible to use gravity assisted alignment in both orthogonal dimensions (x and y) of the workpiece surface. It should be noted that the order in which the two rotations occur is not important; either axis can be rotated first. In some embodiments, both axes are rotated simultaneously. Once proper alignment has been achieved, an electrostatic field can be applied to hold the workpiece  330  in the proper position on the platen  310 . 
     In this embodiment, the major axis is horizontal with respect to the ground, thereby allowing multiple alignments to be performed. The minor axis can be any axis orthogonal to that major axis. Thus, other embodiments of the workpiece support  300  are possible. In some embodiments, the minor or subordinate axis is vertical or horizontal. 
     Returning to  FIG. 8 , the workpiece can be implanted by the ion beam  350  by rotating the platen  310  about the x-tilt axis  345  such that the top surface of the workpiece  330  is facing the oncoming ion beam. Note that rotations about the x-tilt axis and y-tilt axis can be employed if angled implants are desirable. In the case of a scanned implant, the entire workpiece support  300  can be moved vertically or horizontally, as necessary. 
     To align a workpiece with a shadow mask, the following procedure may be used. First, the workpiece is placed on the platen  310 , preferably while it is in the horizontal position, as shown in  FIG. 5 . After the workpiece  330  has been placed on the platen  310 , the platen  310  is then rotated about the y-tilt axis  318 , as shown in  FIG. 6 . This rotation causes the workpiece  330  to move downward toward alignment features  361 , thereby aligning the workpiece  330  and shadow mask  320  in one direction. The platen  310  may be moved to a position which is at an angle of about 60 degrees relative to the horizontal. Angles that are shallower may also be effective in allowing the workpiece  330  to move. This position may be held for between 0.1 and 0.2 seconds to allow the workpiece  330  time to slide to the desired position. Other amounts of time may also be effective. 
     Once the workpiece  330  is in place, the electrostatic field can be applied to the platen  310 , thereby holding the workpiece  330  in this position. In some embodiments, the platen  310  is then returned to the horizontal position, as shown in  FIG. 5 . In the case of one dimensional masks, such as horizontal or vertical lines, the alignment process is completed after alignment is completed in one orientation. 
     In the case of two dimensional masks, the workpiece must be aligned in the orthogonal direction. The platen is then rotated about the x-tilt axis  345  to allow alignment in this direction. In some embodiments, the platen is moved to a position that is at an angle of about 60 degrees relative to the horizontal, although other angles may also be effective. The electrostatic field is disabled to allow the workpiece  330  to slide to the desired position. After the platen  310  is held in the position sufficiently long, such as between 0.1 and 0.2 seconds, the electrostatic field is applied to hold the workpiece  330  in place. At this time, the workpiece  330  and the shadow mask  320  are aligned and ion implantation may begin. 
     In some embodiments, it may be advantageous to tilting the platen  310  about the x and y axes simultaneously.  FIG. 9  shows a workpiece rotated about both the x and y axes simultaneously. In this embodiment, the platen  330  is rotated about both axes simultaneously so that the workpiece  310  can move toward the alignment features  360 , 361  (see  FIG. 7 ). After the workpiece  310  is placed on the platen  330 , the platen  330  is rotated about both axes by about 60 degrees in both directions. In some embodiments, shallower angles may be used to perform the alignment. Once properly rotated, the workpiece  310  will move downward due to the force of gravity. This downward movement aligns the workpiece  310  to both the horizontal and vertical alignment features  2360 ,  361 . The platen  330  is left in this rotated position for between 0.1 and 0.2 seconds, although other amounts of time may also be effective. Once the workpiece  310  is aligned, the electrostatic force may be applied to hold the workpiece  310  in place. 
     Once the workpiece  310  is properly aligned to the shadow mask  320 , the workpiece may be implanted. 
     For a non-angled implant, the platen  310  is rotated 90° so that it is oriented vertically, as shown in  FIG. 10 . For angled implants, the platen  310  can be rotated about the x-tilt axis, the y-tilt axis or both, as required. As stated above, the workpiece support  300  may be moved vertically (or horizontally) to allow scanned implants. 
     The workpiece support  300  can also be used to dismount the workpiece. Note that, as shown in  FIG. 7 , the alignment features  360 ,  361  are only present on one side of the platen  310 . Thus, by rotating the platen  310  in the opposite direction, away from the alignment features, gravity can be used to allow the workpiece  330  to slide away from the features and off of the platen  310  if desired. This can be done by rotation about the x-tilt, the y-tilt axis or both, as desired. 
     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.