Abstract:
A device for holding disk-shaped objects, particularly semiconductor wafers, having at least three contact elements for depositing and/or fixing the disk-shaped object at its outer edge area. The contact elements are designed such that they have an incline facing the object and a supporting surface.

Description:
[0001]    This claims the benefits of German Patent Application No. 10 2008 027 861.0, filed on Jun. 11, 2008 and hereby incorporated by reference herein. 
         [0002]    The present invention relates to a device for holding disk-shaped objects. Preferably semiconductor wafers deposited on and fixed with the device. 
       BACKGROUND 
       [0003]    For the industrial production of chips for the semiconductor industry, integrated circuits are produced on disk-shaped carriers in several consecutive steps. As part of this production process, it is necessary that each disk-shaped carrier, hereinafter also called wafer, is transported from one processing station to another processing station or to an inspecting station. Usually this is done by using a so-called robotic arm, which singulates the wafer from a stack and, for example, supplies it to a means for inspecting the wafer. Such a handling system for wafers with associated robotic arm is known, for example, from US 2003/0031537 A1. The handling system described therein also comprises a robotic arm, which helps to transfer the wafers from a loading station to an inspecting station, wherein a holding means for holding the wafer is provided in the inspecting station. 
         [0004]    When the wafer is transferred to the holding means, it is important to ensure that it is centered as best as possible and that it does not fall out when it is deposited in the holding means. 
         [0005]    Various holding means are already known in this context. For example, U.S. Pat. No. 7,227,628 suggests that, for inspecting the backside of a wafer, the wafer is deposited on a carrier having three support elements. The means for inspecting the wafer is designed as a module. 
         [0006]    For further improvement of the handling, DE 10 2007 010 223 A1 suggests a method for determining geometric parameters of a wafer. The wafer is inserted into a holder having at least three mechanical contacting elements on which the wafer is positioned. The contacting elements are distributed on the holder such that they define a geometric figure which is configured such that the center point of the wafer comes to lie within the geometric figure. The position of each contacting element is determined. Then the desired geometric parameter of the wafer is calculated from the position of the contacting elements. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide a device for holding disk-shaped objects improving the holding reliability and the protection of the disk-shaped object against damage irrespective of the design of the object&#39;s edge. 
         [0008]    The present invention provides a device for holding semiconductor wafers, comprising at least three contact elements for depositing and fixing the semiconductor wafer at its outer edge area, and an incline facing the semiconductor wafer and a supporting surface for the semiconductor wafer are formed at the contact elements. 
         [0009]    The present invention as well provides a contact element for holding a semiconductor wafer has a essential cylindrical form, an incline across the cylinder and a supporting surface at the bottom of the cylinder for receiving the semiconductor wafer. 
         [0010]    Accordingly, the present invention suggests a device for holding disk-shaped objects, particularly semiconductor wafers, having at least three contact elements for depositing and/or fixing the disk-shaped object at its outer edge area. The contact elements comprise an incline facing the object (semiconductor wafer) and a supporting surface. With an incline and a supporting surface provided, an object to be inserted into the holder may slide along the incline to the supporting surface so that even objects inserted at an angle will be securely guided to and held in the desired position. The semiconductor wafers come to rest on the supporting surfaces. 
         [0011]    A frequent application of such devices is the implementation as wafer receiving plate, which may be used for receiving and holding a wafer above a scanner. In order to keep the backside of the wafer nearly completely free for the scanner, the supporting surfaces on which the wafer is deposited should cover the edge area only minimally. For this reason, the contact elements of the inventive device are kept as small as possible. 
         [0012]    In order to ensure a maximally reliable sliding of the object during insertion into the receiving plate, the incline may be chosen to form an angle essentially between 40° and 10° with respect to the normal of the supporting surface. An angle between 30° and 15°, and particularly an angle of 30° or 15°, has proven to be particularly useful. 
         [0013]    The supporting surface can be positioned at the lower end of the incline and may, for example, be designed as a continuous surface. It is also possible to implement the supporting surface as a discontinuous surface, for example in the form of a grid. The supporting length of the supporting surface is preferably between 2 mm and 6 mm, wherein supporting lengths of 3 mm for the fixedly arranged contact elements and of 5 mm for the movably arranged contact elements have proven to be particularly advantageous for securely depositing the object. In a further embodiment of the invention, a particularly secure support may be ensured by choosing essentially 5 mm as the supporting length of all contact elements. 
         [0014]    In a further embodiment of the invention, the contact elements may be arranged at an angle of 120° with respect to each other, wherein two of the contact elements are arranged fixedly and one of the contact elements is arranged to be movable for clamping the object. In that way, tolerances in the outer dimensions of the object may be compensated so that the objects may also be clamped and held with light pressure. It is particularly advantageous if the two fixedly arranged contact elements are arranged in the inlet area of the object, because this ensures that the inlet area of the object is limited. 
         [0015]    The present invention also provides a contact element for holding an object, particularly a semiconductor wafer, wherein the contact element is designed to be essentially cylindrical and comprises an incline across the cylinder and a supporting surface at the bottom of the cylinder for depositing the object. 
         [0016]    The suggested contact element and the suggested device for holding a disk-shaped object advantageously allow the desired securer support and the insertion of the object in a defined position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Further advantages and advantageous embodiments of the invention will be discussed in the following drawings and the associated parts of the description, wherein: 
           [0018]      FIG. 1  schematically illustrates a handling means for handling wafers by means of a robotic arm; 
           [0019]      FIG. 2  schematically illustrates a device for holding a semiconductor wafer; 
           [0020]      FIG. 3  shows a perspective view of an inventive contact element; 
           [0021]      FIG. 4  shows a cross-section of an inventive contact element; and 
           [0022]      FIG. 5  shows a top view of an inventive contact element. 
       
    
    
       [0023]    Throughout the drawings, identical reference numerals refer to elements or functional groups that are identical or have essentially the same function. 
       DETAILED DESCRIPTION 
       [0024]      FIG. 1  schematically illustrates a handling means or handler  10  for handling wafers  12  by means of a robotic arm  14 . A plurality of wafers  12  is accommodated in a loading station  17 . A single wafer  12  is removed therefrom by means of the robotic arm  14  and is transferred to a processing or inspecting station  16 . In the processing or inspecting station  16 , the wafer  12  is usually held in a holding means  18  ( FIG. 2 ). 
         [0025]    The schematic illustration of  FIG. 2  illustrates an embodiment of an inventive device for holding a disk-shaped object by way of the example of a semiconductor wafer  12 . For determining the center point or other geometric parameters of a wafer  12  or for other handling steps, the wafer  12  is inserted in the holding means  18 . The holding means  18  comprises an essentially circular opening  20 , which is designed to be slightly larger than the wafer  12  itself. The holding means  18  is provided with three contact elements  22 ,  24 ,  26 . The wafer  12  is inserted into the opening  20  of the holding means  18  by the robotic arm  14  and, after insertion, is positioned on the supporting surfaces  30  (cf.  FIG. 3 ) of the contact elements  22 ,  24 ,  26 . In order to facilitate bringing the edge  15  of the wafer  12  into mechanical contact with the contact elements  22 ,  24 ,  26 , at least one contact element  26  may be designed to be movable. The movable contact element  26  may be moved along a direction of movement  25 . By means of the movable contact element  26 , the edge  15  of the wafer  12  is brought into contact with the remaining non-movable contact elements  22 ,  24 . 
         [0026]    In order to facilitate the insertion of the wafer  12  and to make it more secure and precise, the contact elements  22 ,  24 ,  26  have a special shape. This shape is mainly characterized by two components, i.e. an incline  28  and a supporting surface  30 .  FIG. 3  is a perspective view schematically and exemplarily showing a contact element  22 , such as it may be used both for the movable contact element  26  and the non-movable contact elements  22 ,  24 . With the help of the specially designed contact elements  22 , the insertion of a wafer  12  may be performed in a more secure and precise way. A wafer  12  inserted into the holding means  18  may slide down the inclines  28  of the contact elements  22 ,  24 ,  26  until it is securely positioned on the supporting surfaces  30 , irrespective of its position in the robotic arm  14 . Particularly if the loading is performed by means of so-called asymmetric end effectors, the result is often that the center of gravity of the wafer  12  gets very close to the connecting line between the ends of the end effectors. When the wafer is inserted into the holding means  18 , the inclines  28  provided on the contact elements  22 ,  24 ,  26  may prevent the wafer  12  from being lifted and from slipping through between the two contact elements  22  and  26 . Instead, the design of the contact elements  22 ,  24 ,  26  including an incline  28  and a supporting surface  30  ensures that the incoming wafer  12  will slide along the incline  28  as desired and will come to rest safely on the supporting surface  30 . In combination with the movable contact element  26 , this then allows clamping the wafer  12  in a simple way in its edge area, as described above. As shown in  FIG. 3 , the contact element  22  may be designed to be essentially cylindrical, wherein the incline  28  is incorporated in one of the cylinder surfaces. In the holding means  18 , the contact element  22 ,  24 ,  26  is positioned such that the incline  28  is oriented towards the wafer  12  to be inserted. For fixation, the contact element  22  may comprise a cavity  29  in its cylinder volume, wherein a means for fastening the contact element  22 , particularly a screw  31 , may be provided on the bottom  27  thereof. For example, a plastic injection molding method using a suitable plastic may be used for the production of the contact elements  22 ,  24 ,  26 . 
         [0027]      FIG. 4  shows a cross-section of an exemplary contact element  22 . As shown, the incline  28  is arranged to be at an angle a with respect to the normal n on the surface of the supporting surface  30 . The angle a preferably has a value essentially between 40° and 10°. The wafer  12  slides particularly well into the supporting surface  30  if the angle a is in the range between 30° and 15° (including the limits of the interval). In practice, particularly good results were achieved when choosing an angle a of 30° or 15°. The supporting length  32  of the supporting surface  30  is selected such that the wafer  12  may be securely supported. However, it must also be taken into account that a minimum of the surface of the wafer  12  should be covered in the supported areas. Therefore a supporting length  32  between 2 mm and 6 mm has proven to be useful for all contact elements  22 ,  24 ,  26 . Good results could be achieved by choosing essentially 3 mm as the supporting length  32  of the supporting surfaces  30  of the fixedly arranged contact elements  22 ,  24 , and 5 mm as the supporting length  32  of the supporting surface  30  of the movably arranged contact element  26 . For particularly secure support, the supporting length  32  may be chosen to be 5 mm for all contact elements  22 ,  24 ,  26 . The supporting surface  30  itself may be implemented as a continuous surface or as a discontinuous surface, such as line or polygon grids. 
         [0028]      FIG. 5  shows a top view of an inventive contact element  22 ,  24 ,  26 . An essentially cylindrical body  34  extends upwards with the supporting length  32  adjacent to the bottom thereof. There may also be seen the bottom  27  of the cavity  29 , where there is provided a fastening means, such as screw  31 . 
         [0029]    The invention has been described with reference to particular embodiments. However, someone skilled in the art will appreciate that modifications and changes may be made to the invention without departing from the scope of the following claims.