Abstract:
An electrostatic clamp which more effectively removes built up charge from a substrate prior to removal is disclosed. Currently, the lift pins and the ground pins are the only mechanism used to remove charge from the substrate after implantation. The present discloses describes an electrostatic chuck in which the top dielectric surface has an embedded conductive region, such as a ring shaped conductive region in the sealing ring. Thus, regardless of the orientation of the substrate during release, at least a portion of the substrate will contain the conductive region on the dielectric layer of the workpiece support. This conductive region may be connected to ground through the use of conductive vias in the dielectric layer. In some embodiments, these conductive vias are the fluid conduits used to supply gas to the back side of the substrate.

Description:
FIELD 
     This disclosure relates to a substrate handling, and more particularly to an apparatus and a method of handling a substrate. 
     BACKGROUND 
     An electronic device may be created from a substrate that has undergone various processes. One of these processes may include introducing impurities or dopants to alter the electrical properties of the original substrate. For example, charged ions, as impurities or dopants, may be introduced to a substrate, such as a silicon wafer, to alter electrical properties of the substrate. One of the processes that introduces impurities to the substrate may be an ion implantation process. 
     An ion implanter is used to perform ion implantation or other modification of a substrate. A block diagram of a conventional ion implanter is shown in  FIG. 1 . The conventional ion implanter may comprise an ion source  102  that may be biased by a power supply  101 . The system may be controller 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 substrate or wafer  114 , which is disposed on a substrate support  116 . 
     In operation, a substrate handling robot (not shown) disposes the substrate  114  on the substrate 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 substrate  114 . After implanting ions is completed, the substrate handling robot may remove the substrate  114  from the substrate support  116  and from the ion implanter  100 . 
     Referring to  FIGS. 2A and 2B , there is shown a block diagram illustrating the workpiece support  116  supporting the substrate  114  during the ion implantation process. As illustrated in  FIG. 2A , the workpiece support  116  may comprise a sealing ring  202  and a plurality of embossments  204  that are in contact with the substrate  114 . The sealing ring may be an annular ring of about 0.25 inches in width, and having a height of 5 microns. The embossments  204  may be about 1 mil in diameter and 5 microns high. In addition, the workpiece support  116  may also include at least one cooling region  206 . During the implantation process, cooling gas may be provided to the cooling region  206  prevent the substrate  114  from overheating. The workpiece support  116  may have gas channels and conduits to allow this cooling gas to flow to the cooling region  206 . The workpiece support  116  may further include a plurality of lift pins  208  that may move so as to push the substrate  114  away from the workpiece support  116  in the direction indicated by the arrows. The lift pins  208  may be retracted within the workpiece support  116 , as illustrated in  FIG. 2B . The workpiece would also be normally in contact with a plurality of ground pins  205 . 
     The workpiece support  116  may be cylindrical in shape, such that its top surface is circular, so as to hold a disc-shaped substrate. Of course, other shapes are possible. To effectively hold the substrate  114  in place, most workpiece supports typically use electrostatic force. By creating a strong electrostatic force on the upper side of the workpiece support  116 , the support can serve as the electrostatic clamp or chuck, and the substrate  114  can be held in place without any mechanical fastening devices. This minimizes contamination, avoids wafer damage from mechanical clamping and also improves cycle time, since the substrate does not need to be unfastened after it has been implanted. These clamps typically use one of two types of force to hold the substrate in place: coulombic or Johnsen-Rahbek force. 
     As seen in  FIG. 2A , the clamp  116  traditionally consists of several layers. The first, or top, layer  210 , which contacts the substrate  114 , is made of an electrically insulating or semiconducting material, such as alumina, since it must produce the electrostatic field without creating a short circuit. In some embodiments, this layer is about 4 mils thick. For those embodiments using coulombic force, the resistivity of the top layer  210 , which is typically formed using crystalline and amorphous dielectric materials, is typically greater than 10 14  Ω-cm. For those embodiments utilizing Johnsen-Rahbek force, the volume resistivity of the top layer, which is formed from a semiconducting material, is typically in the range of 10 9  to 10 12  Ω-cm. The term “non-conductive” is used to describe materials in either of these ranges, and suitable for creating either type of force. The coulombic force can be generated by an alternating voltage (AC) or by a constant voltage (DC) supply. 
     Directly below this layer is a conductive layer  212 , which contains the electrodes that create the electrostatic field. This conductive layer  212  is made using electrically conductive materials, such as silver. Patterns are created in this layer, much like are done in a printed circuit board to create the desired electrode shapes and sizes. Below this conductive layer  212  is a second insulating layer  214 , which is used to separate the conductive layer  212  from the lower portion  220 . 
     The lower portion  220  is preferably made from metal or metal alloy with high thermal conductivity to maintain the overall temperature of the workpiece support  116  within an acceptable range. In many applications, aluminum is used for this lower portion  220 . Other materials, including matrix materials, such as composite materials or ceramics may also be used. 
     Initially, the lift pins  208  are in a lowered position. The substrate handling robot  250  then moves a substrate  114  to a position above the workpiece support  116 . The lift pins  208  may then be actuated to an elevated position (as shown in FIG.  2 A) and may receive the substrate  114  from the substrate handling robot  250 . Thereafter, the substrate handling robot  250  moves away from the workpiece support  116  and the lift pins  208  may recede into the workpiece support  116  such that the sealing ring  202  and the embossments  204  of the workpiece support  116  may be in contact with the substrate  114 , as shown in  FIG. 2B . The ground pins  205  (if used) may in contact with the substrate  114 . The implantation process may then be performed with the lift pins  208  in this recessed position. After the implantation process, the substrate  114  is unclamped from the workpiece support  116 , having been held in place by electrostatic force. The lift pins  208  may then be extended into the elevated position, thereby elevating the substrate  114  and separating the substrate  114  from the sealing ring  202  and the embossments  204  of the workpiece support  116 , as shown in  FIG. 2A . In some embodiments, the lift pins  208  are insulating and therefore may not remove any remaining charge from the substrate  114 . In other embodiments, the lift pins are conductive, such as metallic. The substrate handling robot  250  may then be disposed under the substrate  114 , where it can retrieve the implanted substrate  114  at the elevated position. The lift pins  208  may then be lowered, and the robot  250  may then be actuated so as to remove the substrate  114  from the implanter. 
     A condition that can occur with a conventional ion implanter  100  may be found in the process of removing the substrate  114  from the workpiece support  116 . After multiple cycles of clamping and unclamping a substrate  114  to a workpiece support  116 , the side of the substrate  114  clamped to the workpiece support  116  may exhibit damage. This damage may be due to electrical discharge caused by electrostatic charge buildup on the substrate  114  and the top layer  210  of the workpiece support  116 . The electrostatic charge may discharge (arc) to a ground pin  205  or directly to the surface of the workpiece support  116 . 
     Previously, substrates  114  have been grounded via contact with metal lift pins  208  or ground pins  205 . Substrates  114  also have been grounded previously using a plasma flood gun (PFG). Due to the brief contact time and small contact area between the lift pins  208  or ground pins  205  and the substrate  114  area containing the electrostatic charge, a condition can exist wherein the lift pins  208  and ground pins  205  do not effectively drain the electrostatic charge from the substrate  114 . These ground pins may also cause damage to the backside of the substrate  114 , and may not stay in contact during the entire release sequence. Therefore, the ground pins  205  may successfully ground the substrate  114  during processing or while the substrate  114  is clamped, but may not be able to do so during the wafer release process when the triboelectric charge is generated. Lift pins  208  can be used to release the substrate  114  from the workpiece support  116 . These lift pins  208  may be a conductive metal and will successfully ground the substrate  114  during the entire release sequence. However, metal lift pins  208  can generate metal and particulate contamination as well as damage to the back side of the substrate  114  during release. Therefore, elastomeric lift pins  208  may be used to eliminate contamination and substrate surface damage, however, such pins are insulating and cannot ground the substrate  114  during the release sequence. 
     Accordingly, there is a need in the art for an improved electrostatic clamp that can remove charge, without introducing contamination or damage to the substrate. 
     SUMMARY 
     The problems of the prior art are overcome by the apparatus and method of this disclosure. An electrostatic clamp which more effectively removes built up charge from a substrate prior to removal is disclosed. Currently, the lift pins and the ground pins are the only mechanism used to remove charge from the substrate after implantation. The present disclosure describes an electrostatic chuck in which the top dielectric surface has an embedded conductive region, such as a ring shaped conductive region in the sealing ring. Thus, regardless of the orientation of the substrate during release, at least a portion of the substrate will contain the conductive region on the dielectric layer of the workpiece support. This conductive region may be connected to ground through the use of conductive vias in the dielectric layer. In some embodiments, these conductive vias are the fluid conduits used to supply gas to the back side of the substrate. 
    
    
     
       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. 2A  represents a block diagram showing a workpiece support supporting a substrate with the lift pins extended; 
         FIG. 2B  represents a block diagram showing a workpiece support supporting a substrate with the lift pins recessed; 
         FIG. 3  represents a top view of an embodiment of an electrostatic clamp; 
         FIG. 4  represents a cross-sectional view of the embodiment of  FIG. 3 ; 
         FIG. 5  represents an expanded view of  FIG. 4 ; 
         FIG. 6  represents a top view of a second embodiment of an electrostatic clamp; 
         FIG. 7  represents a top view of another embodiment of an electrostatic clamp; and 
         FIG. 8  represents a cross-sectional view of another embodiment of an electrostatic clamp. 
     
    
    
     DETAILED DESCRIPTION 
     In the present disclosure, several embodiments of an apparatus and a method for handling a processed substrate are introduced. For purpose of clarity and simplicity, the present disclosure will focus on an apparatus and a method for handling a substrate 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, a flood ion implanter, a focused plasma system, a system that modulates a plasma sheath, 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. 
     The embodiments disclosed herein provide a more reliable and lower resistance path to ground for a substrate and the top layer of an electrostatic clamp. Some portion of the substrate will be contacted to ground regardless of how or in what direction the substrate is released from the electrostatic clamp. By providing sufficient charge drainage from the backside surface of the substrate, substrate “sticking” to the electrostatic clamp and substrate breakage can be reduced. 
     Referring to  FIG. 3 , the clamp  300  has an outer annulus or sealing ring  301 . In one instance, the ring  301  may be approximately 0.25 inches in width. Although not shown, the upper surface of the clamp  300  may also have embossments. Lift pins  305  are used to lift the substrate from the clamp  300  after processing of the substrate has been completed. Metal pins  302  may be used to provide additional grounding for the substrate. In other embodiments, the metal pins  302  may be eliminated. 
     Fluid conduits  310  are used to provide gas to the back side of the substrate. These fluid conduits  310  pass through the platen  300 , as shown in  FIG. 4 , and are connected to a gas source  330 . In other words, the fluid conduits  310  may pass through the top layer  304 , conductive layer  306 , the insulating layer  308  and lower portion  320 . In other embodiments, the fluid conduits  310  may exit the platen  300  at a location other than through the bottom, and therefore may not pass through all of these layers. The side walls of the fluid conduits  310  are made of conductive material, even in the non-conductive top layer  304 , and the insulating layer  308 . In addition, the conductive material used for the sidewalls of the fluid conduits  310  is electrically isolated from the material in conductive layer  306 . In other words, the sidewalls of the fluid conduits  310  are electrically connected as they move from one layer to another, but are electrically isolated from the layers through which they pass. Conductive sidewalls may be created using existing technology, such as that used for printed circuit boards, which is known in the art. The sidewalls of the fluid conduits  310  may be electrically connected to the lower portion  320 , which is typically grounded. In other embodiments, the sidewalls are electrically connected to a different ground point. In this way, it is possible to bring a ground connection to the top layer  304  of the platen  300 , where that ground connection is embedded within the platen  300 . 
     As seen in  FIG. 3 , the fluid conduits  310  may be arranged along a ring, which is concentric with the sealing ring  301 , and has a smaller radius. In one embodiment, a conductive ring  340 , located on the top surface, is used to link the sidewalls of these fluid conduits  310  together. This conductive ring  340  is connected to a plurality of the sidewalls of the fluid conduits  310 . In some embodiments, the ring  340  is connected to all of the fluid conduits  310 . 
     As is best seen in  FIG. 2B , the sealing ring  301  contacts the substrate  114  during the processing of the substrate  114 , as well as during the release. Therefore, it is important to provide one or more ground contacts on the sealing ring  301 . In the embodiment shown in  FIG. 3 , a second conductive ring, or a conductive sealing ring,  345  is formed on the sealing ring  301  and is connected to conductive ring  340  through one or more conduits  347 . In some embodiments, conduits  347  are spokes which extend across the diameter of the platen  300 . In some embodiments, three conduits  347  are used, but the number of conduits is not limited to a particular number. 
     The use of conduits  347  serves several purposes. First, these conduits  347  provide redundant paths between the conductive ring  340  and the conductive sealing ring  345 . In the event of a break in either conductive ring  340 ,  345 , the conduits  347  provide alternate current paths. Secondly, these conduits  347  lower the effective resistance between the conductive ring  340  and the conductive sealing ring  345 . 
       FIG. 5  shows an expanded cross-sectional view, showing the electrical connection between the conductive ring  340  and the conductive sealing ring  345 . In this embodiment, a conduit  347  electrically connects these rings  340 ,  345  together. The conductive ring  340  and conductive sealing ring  345  and the conduit  347  may be a conductive or semi-conductive material, such as pure aluminum or heavily doped DLC (diamond-like carbon). This material may be deposited on, or embedded in the top layer  304 , such as by CVD (chemical vapor deposition) or PE CVD (plasma enhanced chemical vapor deposition). In one embodiment, a metal, such as aluminum, is deposited on the surface of the top layer  304 . In other embodiments, the use of a metal conductive material may lead to contamination of semiconductor wafers. Therefore, in other embodiments, non-metallic conductors, such as diamond-like carbon (DLC) and silicon carbide (SiC) doped with nitrogen may be used. These non-metallic conductors may be deposited using PECVD. In other embodiments, a metal conductor is deposited on the top layer  304 , and a non-metallic conductor is deposited on top of the metal. This reduces the risk of contamination and increases the conductivity of the electrical conduit. 
       FIG. 4  shows a cross-section view of the clamp  300  of  FIG. 3 . As described above, the lower portion  320  of the electrostatic clamp  300  is typically made of a metal, and is typically connected to ground. Therefore, in some embodiments, the sidewalls of the fluid conduits  310  are in contact with the lower portion  320  of the electrostatic clamp  300 , and are grounded accordingly. In other embodiments, the sidewalls of the fluid conduits  310  are connected to a different ground source. 
       FIG. 3  illustrates conduits  347  extending across the diameter of the electrostatic clamp  300 . However, other embodiments are possible. For example, the conduits  347  may only extend outwardly from the conductive ring  340  to the conducting sealing ring  345 , as shown in  FIG. 6 . 
     In another embodiment, the sidewalls of the fluid conduits  310  are in electrical contact with the conductive sealing ring  345 , without the use of a conductive ring  340 .  FIG. 7  shows an embodiment in which the sidewall of each fluid conduit  310  is electrically connected to the sealing conductive ring  345 . In other embodiments, a subset of the sidewalls is connected to the conductive sealing ring  345 . 
     Other configurations which utilize the fluid conduits  310  to provide a ground connection to the top surface of the platen  300  may also be used and are within the scope of the disclosure. 
     In some embodiments, the conductive sealing ring  345  is permanently connected to ground. This is due to the generally high resistivity of the top surface  304 , which limits the effect of the grounded sealing ring  345 . However, in some embodiments, the sealing ring  345  may be intermittently connected to ground (i.e. active ground connection). For example, using a switch or other device, the ground connection to the fluid conduits  310  or to the conductive sealing ring  345  may be interrupted while the electrodes are actively generating an electrostatic field. In other words, the switch is in series between the sealing ring  345  and ground, such that actuation of the switch either enables or disables the connection to ground. When the electrodes  306  are inactive, the grounding connection may be restored. This modification insures that the grounding of the top surface  304  of the clamp  300  has minimal or no impact on the electrostatic clamp force. 
     While one embodiment utilizes the fluid conduits  310  to carry ground to the top layer  304 , other embodiments are possible. For example, as seen in  FIG. 8 , conductive regions, different from the fluid conduits  310 , may be used to form a conductive path  360  which may bring ground to the top layer  304 . These regions may be embedded in the platen  300 . For example, each layer may be formed such that a region of each layer  304 , 306 , 308  is made of a conductive material, such that, when assembled, the regions of conductive material are aligned and form a conductive path  360  to the top layer  304 . These regions can be connected to the grounded lower portion  320 , or another ground. In some embodiments, the regions are located such that the conductive path  360  terminates in the sealing ring  301 . One or more regions can be used to form conductive paths  360  that connect ground to a conductive sealing ring  345 . In another embodiment, the conductive path  360  is located away from the sealing ring  301 , so that conductive conduits, such as conduits  347  (see  FIG. 7 ) must be added to the top layer  304  to connect the conductive sealing ring  345  to conductive ground path  360 . In other embodiments, the conductive path  360  is located along the outer edge of the platen  300 . 
     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.