Abstract:
A wafer support for supporting a semiconductor wafer during a process including varied temperature. The wafer support includes a body having a top surface adapted to receive the semiconductor wafer so a portion of the top surface supports the wafer. The top surface has a recessed area including an inclined surface rising from a bottom of the recessed area. The inclined surface has an incline angle that is no more than about ten degrees.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to apparatus for supporting a semiconductor wafer in a high temperature environment, and more particularly to such apparatus and methods adapted to limit damage to the semiconductor wafer. 
         [0002]    Semiconductor wafers commonly undergo high temperature heat treatment (e.g., annealing) to achieve certain desirable characteristics. For example, high temperature heat treatment may be used to create a defect free layer of silicon on the semiconductor wafers. The high temperature annealing process is typically carried out in a vertical furnace which subjects the wafers to temperatures of at least about 1100 degrees centigrade, most commonly between about 1200 degrees centigrade and about 1300 degrees centigrade. Semiconductor wafers may also be subjected to various other high temperature heat treatment processes, e.g., rapid thermal processing (RTP), to achieve various wafer characteristics that may be desired. 
         [0003]    Semiconductor wafers become more plastic at the high temperatures associated with high temperature heat treatment. For example, silicon wafers become more plastic at temperatures above 750 degrees centigrade and especially at temperatures above 1100 degrees centigrade. If the semiconductor wafers are not adequately supported during heat treatment, the wafers may undergo slip due to gravitational and thermal stresses. As is well known in the art, slip may introduce contaminants into the device areas of the wafers. Moreover, excessive slip may cause the wafers to plastically deform, leading to production problems, such as photolithography overlay failures causing yield losses in device manufacture. 
         [0004]    The wafer support is usually constructed of a different material than the semiconductor wafer. For example, wafer supports are often constructed of silicon carbide (SiC) because this material remains relatively strong when subjected to the high temperatures encountered during high temperature heat treatment. However, there can be a mismatch in the coefficients of thermal expansion if the wafer support is made of a different material than the semiconductor wafer. Thermal mismatch may cause the wafer to slide on surfaces of the wafer support during heating and cooling. 
         [0005]      FIGS. 1 and 2  illustrate a prior art wafer support is used to support semiconductor wafers in high temperature environments. This prior art wafer support is constructed of SiC and has an open C-shaped configuration. This configuration allows wafers to be robotically loaded and unloaded from the wafer support. The wafer support has a top surface that engages the wafer to support the wafer. There is an arcuate groove about 0.2 millimeter (mm) deep and about 30 mm wide in the top surface of the wafer support. The purpose of this groove is to prevent the wafer from floating on top of the wafer support during loading and also to prevent the wafer from sticking to the wafer support during unloading. The inner and outer edge margins of the groove are often broken edges and the shape of these edges cannot be finely controlled by machining due to difficulties in machining SiC. The inventors have observed a tendency for the edges of the groove of the prior art wafer support to damage the semiconductor wafer. Damage inflicted on the wafer by the groove reduces wafer yield. 
       SUMMARY 
       [0006]    In one aspect, the present invention includes a wafer support for supporting a semiconductor wafer during a process including varied temperature. The wafer support comprises a body having a top surface adapted to receive the semiconductor wafer so a portion of the top surface supports the wafer. The top surface has a recessed area including an inclined surface rising from a bottom of the recessed area. The inclined surface has an incline angle that is no more than about ten degrees. 
         [0007]    In another aspect, the present invention includes a wafer support for supporting a semiconductor wafer in a heat treatment process. The wafer support comprises a body having a top surface adapted to engage the semiconductor wafer with at least a portion of the top surface supporting the wafer. The top surface has an outer edge and a recessed area having a inner limit and an outer limit. The inner and outer limits are substantially free of broken edges inside the outer edge of the top surface. 
         [0008]    In still another aspect, the present invention includes a wafer support for supporting a semiconductor wafer during a process including varied temperature. The wafer support comprises a body having a top surface adapted to receive the semiconductor wafer so a portion of the top surface supports the wafer. The top surface has a recessed area including an inclined outer margin rising from a bottom of the recessed area. The inclined outer margin has an incline angle that is no more than about five degrees. 
         [0009]    In yet another aspect, the present invention includes a wafer support for supporting a semiconductor wafer during a process including varied temperature. The wafer support comprises a body having a top surface adapted to receive the semiconductor wafer so a portion of the top surface supports the wafer. The top surface has a recessed area and a rounded ridge extending around the body inside the recessed area. The recessed area includes an inner margin formed by at least a portion of the rounded ridge. The inner margin has a maximum incline angle that is no more than about ten degrees. 
         [0010]    The present invention also includes a wafer support for supporting a semiconductor wafer during a process including varied temperature. The wafer support comprises a body having a top surface adapted to receive the semiconductor wafer so a portion of the top surface supports the wafer. The top surface has a constant slope between a higher outer edge and a lower inner edge. 
         [0011]    In another aspect, the present invention includes a wafer support for supporting a semiconductor wafer during a process including varied temperature. The wafer support comprises a body having a top surface adapted to receive the semiconductor wafer so a portion of the top surface supports the wafer. The top surface has a slope at a higher outer edge and a substantially equal slope at a lower inner edge. 
         [0012]    Other objects and features will be in part apparent and in part pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a plan view of a prior art wafer support; 
           [0014]      FIG. 2  is an enlarged section of a portion of the prior art wafer support taken in a plane including line  2 - 2  on  FIG. 1 ; 
           [0015]      FIG. 3  is a plan view of a first embodiment of a the wafer support of the present invention; 
           [0016]      FIG. 4  is an enlarged section of a portion of the wafer support of the first embodiment taken in a plane including line  4 - 4  of  FIG. 3 ; 
           [0017]      FIG. 5  is a plan view of a second embodiment of a the wafer support of the present invention; and 
           [0018]      FIG. 6  is an enlarged section of a portion of the wafer support of the second embodiment taken in a plane including line  6 - 6  of  FIG. 5 . 
       
    
    
       [0019]    Corresponding reference characters indicate corresponding parts throughout the drawings. 
       DETAILED DESCRIPTION 
       [0020]    Referring to  FIGS. 3 and 4 , a first embodiment of a wafer support of the present invention, generally designated  101 , comprises a body  103  adapted to engage a semiconductor wafer (e.g., a silicon wafer, not shown) and support the wafer in a high temperature environment. For example, the wafer support  101  is suitable for use in a process in which the wafer is annealed at a high temperature in a furnace. The wafer support  101  is also suitable for supporting the wafer as it is heated from a relatively low temperature to a relatively high temperature and/or cooled from the relatively high temperature to the relatively lower temperature. 
         [0021]    In this embodiment, the body  103  has a C-shaped configuration. As illustrated in  FIG. 3 , the body  103  is a generally circular ring segment. A top surface  105  of the body  103  is generally flat (except as noted) for engaging a back of the substantially flat semiconductor wafer. The wafer support  101  can have various orientations when not in use and the top surface  105  may not be the top of the body  103 , depending on the orientation of the wafer support at the time. For convenience, the surface facing up in use is referred to as the top surface  105 . The wafer support  101  is capable of withstanding an environment having a temperature in excess of 1050 degrees centigrade (e.g., about 1200 degrees centigrade). For instance, the wafer support  101  may be constructed of silicon carbide (SiC). In one embodiment, the body  103  is a unitary body as illustrated in  FIGS. 3 and 4 . 
         [0022]    The body  103  has opposing ends  111  defining an opening  113  in one sector of the body. The ends  111  are spaced from one another by a distance sufficient to provide clearance for a robotic arm (not shown) to extend between the ends to access an internal space that is partially enclosed by the C-shaped body  103  when the robot automatically loads and unloads the wafer from the wafer support  101 . For example, the opposing ends  111  of the illustrated embodiment are spaced from one another by a distance D in a range from about 50 millimeters (mm) to about 150 mm. The top surface  105  of the wafer support  101  has an outer edge  121  having a diameter DO in a range from about 300 mm to about 310 mm. In one embodiment, the outer edge  121  has a diameter of more than about 300 mm (e.g., about 360 mm) for processing 300 mm diameter wafers. The top surface  105  of the wafer support  101  has an inner edge  123  having a diameter Di in a range from about 190 mm to about 210 mm. Further, the body  103  has a width W in a range from about 45 mm to about 60 mm. 
         [0023]    The top surface  105  of the wafer support  101  includes a broad arcuate groove  131 . This groove  131  reduces the potential for the wafer to float above the top surface  105  of the wafer support  101  as it is loaded. The groove  131  also reduces the potential for the wafer to stick to the wafer support  101  during unloading. In the embodiment illustrated in  FIGS. 3 and 4 , the groove  131  extends from one end  111  of the wafer support  101  to the other along an arc having a center that is coincident with the center of the circular body  103 . Thus, in this embodiment, the arcuate groove  131  is concentric with the C-shaped body  103  of the wafer support  101 . As illustrated, the groove  131  extends continuously along the body  103  and has a substantially uniform width WG. The groove width WG can vary within the scope of the invention. For example, in one embodiment, the groove  131  has a width WG in a range from about 15 mm to about 50 mm. It is envisioned that in some embodiments, the groove width WG can vary along its length and/or the groove  131  can be non-concentric with respect to the body  103 . 
         [0024]    As shown in  FIG. 4 , the groove  131  has a generally planar bottom  133  extending between a crowned ridge  135  and an inclined outer margin  137 . The crowned ridge  135  forms a machined surface upon which the wafer rests. Because the ridge  135  is machined, it provides a smooth surface that reduces potential for damaging the back of the wafer. Although the ridge  135  may have other roughnesses without departing from the scope of the present invention, in one embodiment, the ridge  135  has a surface roughness of less than about 2 micrometers (μm) roughness average (Ra). Although the ridge  135  may have other smooth cross-sectional shapes without departing from the scope of the present invention, in one embodiment the cross section has a rounded shape. In one particular embodiment, the ridge  135  has a cross section that is a segment of a circle having a maximum incline angle of no more than about 10°. In some embodiments, the ridge  135  has a cross section that is a segment of a circle having a maximum incline angle of no more than about 5°. In still other embodiments, the ridge  135  has a cross section that is a segment of a circle having a maximum incline angle of no more than about 2.5°. Further, in some embodiments, the ridge  135  rises about 0.2 mm above the bottom  133  of the groove. In the illustrated embodiment, the elevations of the inner ridge  135  and the outer edge  121  are about equal. 
         [0025]    In some embodiments, the inclined outer margin  137  has a generally constant slope from the bottom  133  of the groove  131  to the outer edge  121  of the body  103 . In one embodiment, the inclined outer margin  137  slopes at an incline angle of about 5°. In some embodiments, the margin  137  slopes at an incline angle of about 2.5°. In still other embodiments, the margin  137  slopes at an incline angle of about 1°. In some embodiments the margin  137  extends to the outer edge  121  of the top surface  105 . Although the outer margin  137  may have other widths without departing from the scope of the present invention, in some embodiments the inclined outer margin has a width WO of about 2 mm. 
         [0026]    In some embodiments, the body  103  can optionally include multiple pieces and may be configured differently (e.g., as a round plate, closed ring, or other shape that does not have any opening for use by a robot arm) within the scope of the invention. Likewise, the body  103  can be made from materials other than SiC within the scope of the invention. 
         [0027]    Referring to  FIGS. 5 and 6 , a second embodiment of a wafer support of the present invention, generally designated  201 , comprises a body  203  adapted to engage a semiconductor wafer (e.g., a silicon wafer, not shown) and support the wafer in a high temperature environment. In this embodiment, the body  203  has a C-shaped configuration. As illustrated in  FIG. 5 , the body  203  is a generally circular ring segment. A top surface  205  of the body  203  is generally conical for engaging an outer edge of a back of the substantially flat semiconductor wafer. 
         [0028]    The body  203  has opposing ends  211  defining an opening  213  in one sector of the body. The ends  211  are spaced from one another by a distance sufficient to provide clearance for a robotic arm (not shown) to move between the ends to access an internal space that is partially enclosed by the C-shaped body  203  when the robot automatically loads and unloads the wafer from the wafer support  201 . For example, the opposing ends  211  of the illustrated embodiment are spaced from one another by a distance D in a range similar to the support of the first embodiment. The top surface  205  of the wafer support  201  has an outer edge  221  having a diameter DO in a range similar to the support of the first embodiment. In one embodiment, the outer edge  221  has a diameter of more than about 300 mm (e.g., about 360 mm) for processing 300 mm diameter wafers. The top surface  205  of the wafer support  201  has an inner edge  223  having a diameter DI in a range similar to the support of the first embodiment. Further, the body  203  has a width W in a range similar to the support of the first embodiment. 
         [0029]    In some embodiments, the top surface  205  has a generally constant slope from the inner edge  223  to the outer edge  221  of the body  203 . It is envisioned in some embodiments the slope may vary radially and/or circumferentially without departing from the scope of the present invention. In one embodiment, the top surface  205  slopes at an incline angle of about 5°. In some embodiments, the top surface  205  slopes at an incline angle of about 2.5°. In still other embodiments, the top surface  205  slopes at an incline angle of about 1°. 
         [0030]    In some embodiments, the body  201  can optionally include multiple pieces and may be configured differently (e.g., as a round plate, closed ring, or other shape that does not have any opening for use by a robot arm) within the scope of the invention. Likewise, the body  201  can be made from materials other than SiC within the scope of the invention. 
         [0031]    When introducing elements of the present invention or the preferred embodiments thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0032]    In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
         [0033]    As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.