Abstract:
The invention relates to a carrier for a substrate, wherein at least parts of the carrier are comprised of a material with a coefficient of thermal expansion which is higher than the coefficient of thermal expansion of the substrate. In order to avoid, or at least decrease, the nonuniform coating of the substrates at the margins, in particular during sputtering processes, a web is centrally connected with the carrier. This web has a lower coefficient of thermal expansion than the region of the carrier on which it is fastened.

Description:
FIELD OF THE INVENTION  
       [0001]     This application claims priority from German Pat. application No. 10 200 045 718.5 filed Sep. 24, 2005, incorporated herein by reference in its entirety.  
         [0002]     The invention relates to a substrate carrier.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0003]     Substrates are often guided in sputter units past a so-called target, from the surface of which particles are sputtered off, which are deposited on the substrate. As the substrates can be utilized, for example, glass plates, which are transported through an inline sputter unit. These glass plates are set into a frame connected with a transport device.  
         [0004]     A device for the transport of substrates into and through vacuum treatment units, for example, is known, which comprises a bulky foot part composed of two wheel sets correlated with one track and one support bearing (DE 41 39 549 A1). The substrates to be treated are herein held by means of a rectangular substrate holder.  
         [0005]     Furthermore is known an annular substrate holder for the mounting of a round substrate plate, this substrate holder, in turn, being held by four equally distributed holding arms (DE 102 11 827 C1).  
         [0006]     If the substrates held in frames have a coefficient of thermal expansion different from that of the frames, the substrates may be covered at the margins nonuniformly and onesidedly to too high a degree. In the case of wafers this is referred to as “edge exclusion”, i.e. to a peripheral region of the wafer which is not coated.  
         [0007]     The invention therefore addresses the problem of providing a carrier for substrates, in which the substrates are covered uniformly and not too thickly at the margin.  
         [0008]     The problem is resolved according to the present invention, which relates in part to a carrier for a substrate, wherein at least parts of the carrier are comprised of a material having a coefficient of thermal expansion which is higher than the coefficient of thermal expansion of the substrate. To avoid, or at least decrease, nonuniform coating of the substrate at the margins, in particular during sputter processes, a web is centrally connected with the carrier. This web has a coefficient of thermal expansion lower than the region of the carrier at which it is fastened.  
         [0009]     The advantage attained with the invention resides in particular therein that through the combination of lightweight cost-effective aluminum, which expands to a high degree, with a centering means of a material, which expands to a lesser degree, for example titanium, the “edge exclusion” is reduced.  
         [0010]     An embodiment example of the invention is shown in the drawing and will be described in further detail below: 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0011]      FIG. 1   a  to  1   c  shows fundamental representation of a substrate carrier with a substrate at different thermal expansions.  
         [0012]      FIG. 2  shows a frame-form substrate carrier with a web of a material with relatively low coefficient of thermal expansion, for example titanium.  
         [0013]      FIG. 3   a  to  3   c  shows schematic illustrations to explain the operational function of the invention.  
         [0014]      FIG. 4  shows a section B-B through the device of  FIG. 3   a.   
     
    
     DETAILED DESCRIPTION  
       [0015]      FIG. 1   a  to  1   c  depict the principle of the support of an areal substrate  2  on webs  3 ,  4  of a conventional substrate carrier  1 . The set of problems to be resolved will be demonstrated in conjunction with this figure. The substrate will be assumed to be glass, while the substrate carrier  1  is comprised of aluminum.  
         [0016]      FIG. 1   a  shows the state at approximately 20° C. (0° C.=273.15° K, i.e. 20° C.=293.15° K). Ends  40 ,  41  of the substrate  2  abut projections  42 ,  43  of webs  3 ,  4 . By  44  is denoted that side of substrate  2  which is to be coated. In the position depicted in  FIG. 1   a  of the substrate  2  those regions a, b, which are covered by the webs  3 ,  4 , would not be coated when sputtered. The regions a and b are of equal size.  
         [0017]     However, sputtering takes place at a temperature which is, for example, higher by 220° K (=appr. 513.15° K), at which glass and aluminum expand differently. The illustrations of  FIG. 1   b  and  1   c  show the effect of this different expansion. The webs  3 ,  4  of aluminum, connected with one another—the connections are not shown—migrate considerably further toward the side than the substrate  2 . Therein two different constellations may result, of which the one is depicted in  FIG. 1   b  and the other in  FIG. 1   c.    
         [0018]     As has been found in practice, one of the end regions  45 ,  46  of substrate  2  always rests more firmly on webs  3 ,  4  than does the other, with the result that one end region—in  FIG. 1   b  the end region  46 —moves away from projection  42 , while the other end region  45  retains its original position.  
         [0019]     The substrate  2  is hereby nearly completely coated in the end region  46 , while the end region  45  remains uncoated.  
         [0020]      FIG. 1   c  illustrates the case in which the end region  46  remains in its original position, while the end region  45  migrates relative to web  4 .  
         [0021]     In  FIG. 1   b  consequently “edge exclusion” occurs in end region  45 , in  FIG. 1   c , in contrast, in end region  46 .  
         [0022]     If the substrate is a glass plate of 1950 mm width, and if the temperature difference is, for example, ΔT=220° K, the thermal expansion of the glass is 1.6 mm and of aluminum the thermal expansion is 10.2 mm. Segment l is consequently 8.6 mm.  
         [0023]      FIG. 2  shows a substrate carrier  1  according to the invention with the substrate  2 . Substrate  2  is again a glass plate. The substrate carrier  1  is formed essentially by a frame with two vertical webs  3 ,  4  and two horizontal plates  5 ,  6 . The vertical webs  3 ,  4  are for example webs of titanium. However, they may also be comprised of another material. The horizontal plates  5 ,  6  preferably comprise aluminum and are connected with bolts or rivets  7 ,  8 ,  9 ,  10  or  11  to  16 , respectively, with the ends of the vertical webs  3 ,  4 . Closely beneath the substrate  2  extends a relatively thin web  17  of titanium, which at each of its ends has an upwardly directed finger  18 ,  19 . This web  17  is centrally connected with bolts  20  or the like with the aluminum plate  6 . In the aluminum plate  6  beneath web  17  is provided a, not shown, groove by which the titanium web  17  is guided.  
         [0024]     If the substrate  2  without web  17  and fingers  18 ,  19 —i.e. residing only in contact on the aluminum plates  5 ,  6 —is transported through a heated sputter chamber, the aluminum plates  5 ,  6  expand to a greater degree than the substrate  2  comprised of glass. Webs  3 ,  4  consequently move away from one another—as depicted in  FIG. 1   a  to  1   c —which means that the substrate  2  is no longer delimited by these webs  3 ,  4 . Substrate  2  can be on web  3  with its left edge (cf.  FIG. 1   c ) as well as with its right edge (cf.  FIG. 1   b ) on web  4 . In neither case is it any longer located centrally with respect to webs  3 ,  4 , which can lead to nonuniformly coated margins of substrate  2 .  
         [0025]     If, in contrast, the substrate is located between fingers  18 ,  19  of the titanium web  17 , the substrate  2  remains centered, since the titanium web  17  is connected in its center with the center of the aluminum plate  6 . The titanium web  17  migrates symmetrically with respect to bolt  20  toward the left and the right.  
         [0026]     Since titanium has a significantly lower coefficient of thermal expansion than aluminum, the substrate  2  shifts only slightly relative to fingers  18 ,  19 . Consequently, it remains centered relative to the vertical webs  3 ,  4 .  
         [0027]     This is once again shown in principle in  FIG. 3   a  to  3   c.    
         [0028]      FIG. 3   a  shows the state at approximately 20° C. The fingers  18 ,  19  of titanium web  17  abut, on the one hand, the projections  42 ,  43  and, on the other hand, the ends  40 ,  41  of the substrate.  
         [0029]     At a temperature increased for example by 220° K, either the constellation according to  FIG. 3   b  results or the constellation according to  FIG. 3   c.    
         [0030]     Since with increasing heat titanium expands considerably less than aluminum, substrate  2  has only slight tolerance c or d, respectively, with respect to finger  19  or  18 , respectively, of the titanium web  17 . The coating of substrate  2  is consequently significantly more uniform than in the case of  FIG. 1   b  and  1   c . At a temperature difference of 220° K the titanium web  17  expands only by 3.5 mm at an assumed width. The distances c and d therewith are only 1.9 mm. Instead of titanium, other materials with lower thermal expansion can be utilized, for example ceramics, which are optionally reinforced with glass fibers.  
         [0031]     In  FIG. 4   a  section B-B through the configuration according to  FIG. 3   a  is shown. The fingers  18 ,  19  of titanium web  17  are herein again evident. The frames  3 ,  4 ,  50  are herein comprised throughout of the same material, for example aluminum.