Patent Publication Number: US-2005133073-A1

Title: Substrate carrier for receiving and retaining in position a planar element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority of the German patent application 103 59 732.8, filed Dec. 19, 2003, which is incorporated by reference herein.  
     FIELD OF THE INVENTION  
      The invention concerns a substrate carrier for receiving and retaining in position a planar element.  
     BACKGROUND OF THE INVENTION  
      In semiconductor production, wafers are sequentially processed in a plurality of process steps during the production process. With increasing integration density, demands in terms of the quality of the features configured on the wafers, and in terms of secure wafer handling, are rising. “Handling” is understood to mean the transfer of a wafer from one station to the next. Substrate carriers are indispensable resources for temporary holding and retention in position for mechanical processing, cleaning, and inspection of semiconductor substrates in microelectronics and optoelectronics technology. In the case of substrates produced on an industrial scale, the carriers are usually disk-shaped.  
      At present, the substrates to be processed are adhesively bonded onto the substrate carriers or, if the carrier is appropriately configured, are held in place by negative pressure (a vacuum).  
      German unexamined Application 44 25 874 discloses a substrate carrier for receiving and temporarily retaining a planar element in position. Retention of the planar element is achieved with vacuum. For that purpose, the contact surface has a plurality of openings through which the negative pressure acts on the planar element.  
      U.S. Pat. No. 6,563,195 discloses a carrier for a wafer having a dust-protection film. For transport, the wafer rests on silicone rubber. Before placement, a protective film provided on the silicone rubber is removed. This patent also does not disclose the use of a plastic for the various handling systems for a wafer.  
     SUMMARY OF THE INVENTION  
      It is the object of the invention to create a universally usable and easily handled substrate carrier with which retention of substrates is possible in simple fashion. Transport of the substrate in any desired direction and position in space is also intended to be possible.  
      This object is achieved by way of a substrate carrier, for receiving and retaining a planar element in position, comprising at least one plastic support provided on the substrate carrier; wherein the planar element is held exclusively by means of adhesion.  
      It is particularly advantageous if at least one plastic support is provided on the substrate carrier; and that the planar element is held exclusively by means of adhesion. Advantageously, the substrate carrier can be a pull-out finger for a planar element or a semiconductor substrate. The substrate carrier can also be a changer for a planar element or a semiconductor substrate. A wafer chuck for a planar element or a semiconductor substrate is likewise conceivable as the substrate carrier. Lastly, the substrate carrier can be an end effector (end/edge holder) for a planar element or a semiconductor substrate. The plastic support is made of an elastomer or a thermoplastic.  
      It is particularly advantageous if the plastic support on the substrate carrier is subdivided into several individual plastic supports, the plastic supports together forming an overall surface which is calculated in such a way that the adhesion forces are sufficient to hold the planar element. The overall surface of the plastic supports for the planar element is calculated as a function of the diameter and the weight of the planar element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The subject matter of the invention is depicted schematically in the drawings and will be described below with reference to the Figures, in which:  
       FIG. 1  schematically depicts the configuration of the complete system for handling wafers;  
       FIG. 2  depicts, in perspective, a pull-out finger for semiconductor substrates or wafers;  
       FIG. 3  depicts, in perspective, a changer for semiconductor substrates or wafers;  
       FIG. 4  depicts, in perspective, a wafer chuck for semiconductor substrates or wafers; and  
       FIG. 5  depicts, in perspective, an end effector for semiconductor substrates or wafers.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  shows, by way of example, a three-dimensional view of a substrate delivery module  1  and workstation  3 . Two transfer stations  2 a,  2 b for the substrates are associated with the substrate delivery module. This overall external view also shows a monitor  7  with which the user can check his inputs made via operating interface  6 , track the status of substrate handling, or view results of the work processes in workstation  3 , etc. Images of the substrate can also be displayed on monitor  7  in the event a camera is installed in workstation  3 , or the substrate can be observed directly with a microscope via a microscope viewing port  8 . During examination or treatment, the substrates are transported back and forth between transfer stations  2 a,  2 b, delivery module  1 , and workstation  3 . The substrate rests on a substrate carrier (not depicted in  FIG. 1 ).  
      The substrate carrier is for receiving and retaining any desired element in position, in particular a semiconductor substrate (wafer), for the manufacture of electronic or optical components on the wafer.  
      Retention is accomplished substantially by way of the adhesion forces that occur between the support surfaces and the substrate.  
      The adhesion forces that occur are proportional to the size of the support surfaces. In production processes in the semiconductor industry, substrate carriers that can retain substrates having a standardized size (at present, approximately 50 to 300 mm) are usually used. In flexible production facilities designed for smaller production runs, however, as well as facilities used for research and testing purposes, a configuration of the substrate carriers for receiving and retaining substrates of various diameters, as well as substrate fragments, is desirable.  
       FIG. 2  depicts a pull-out finger  20  for semiconductor substrates or wafers  21  (drawn with dashed lines). Pull-out finger  20  encompasses an arm region  22  and a support region  23 . Support region substantially comprises a first finger  23 a and a second finger  23 b. A cutout  24  is embodied between first finger  23 a and second finger  23 b. Arranged around cutout  24  are several plastic supports  25  that are immovably joined to first finger  23 a and second finger  23 b of pull-out finger  20 . The plastic supports on the substrate carrier or pull-out finger  20  define in their entirety a support surface  26  for the planar element or wafer  21 , that surface being determined as a function of the diameter and weight of the planar element or wafer  21 .  
       FIG. 3  depicts a changer  30  for semiconductor substrates or wafers. Changer  30  is rotatable about an axis  31  and comprises a first arm  32  and a second arm  33 . First and second arms  32  and  33  are arranged at 180 degrees from one another. First and second arms  32  and  33  each have an end  34  that has a respectively configured hook-shaped protrusion  35 . Protrusion  35  and end  34  each carry plastic supports  25 . Corresponding to the necessary support surface  26  of plastic supports  25 , the same conditions as already described in  FIG. 2  apply. The embodiment of changer  30  depicted here is not to be construed as a limitation. Changer  30  can also have more than two arms.  
       FIG. 4  depicts a wafer chuck  40  for semiconductor substrates or wafers (not shown here). Wafer chuck  40  is of annular configuration and comprises an opening by way of which a transfer of the wafer onto the wafer chuck is performed. For example, a wafer handler can be lowered through opening  41  after the wafer has been placed onto wafer chuck  40 . The wafer chuck possesses a plurality of plastic supports  25 . The same conditions as already described in  FIG. 2  apply to support surface  26  of plastic supports  25 .  
       FIG. 5  depicts an end effector  50  for semiconductor substrates or wafers (not shown here). End effector  50  is mounted on a robot (not shown) that places the wafers in a magazine. End effector  50  encompasses an arm  51  that has a fork-shaped configuration  53  at one end  52 . Fork-shaped configuration  53  encompasses at least two fingers  54  and a base  55 . Fingers  54  and base  55  are provided with several plastic supports  25 . Plastic supports  25  form support surface  26  for the wafers.  
      The support surfaces of the plastic supports on which the substrate or wafer rests are made of an elastomer or a thermoplastic. The thermoplastic can be embodied as soft PVC. The dust-catching mats that are used in clean rooms are one example of soft PVC. Plastic support  25  is substantially characterized by its high adhesion forces. One selected material is a soft PVC that is manufactured by the company Kager Industrieprodukte. The properties exhibited by the material were ascertained in tests. An ascertained tensile/shear strength of 0.06 N/mm 2  was obtained, and the tensile strength ascertained was 0.02 N/mm 2 . These values apply to the “Weich PVC Rutschstopp” plastic that was used. It is self-evident that these ascertained values represent only a guideline. Other plastics with similar data can also be used.  
      As already mentioned in the description of the Figures, the necessary support surface area is obtained as a function of the diameter and weight of the wafer. If the wafer must also be safely handled upside down, the size of support surfaces  26  of plastic supports  25  must also be determined in consideration of the weight of the wafer and a requisite safety factor. When the plastic for plastic supports  25  is selected, care must be taken to avoid contamination of the wafer being handled. The plastic is either adhesively bonded, or secured to the substrate carrier with a different method (evaporatively deposited or melted on). Although four specific embodiments of a substrate carrier are depicted in the description above, the shape of the substrate carrier is arbitrary. Plastic supports  25  can likewise have any desired shape.