Abstract:
A substrate holding apparatus for holding substrates in vertical posture includes a first holder, a second holder and a substrate fall preventing stand arranged along edges of the substrates and located below centers of the substrates. The first holder is disposed in a position for holding the substrates between lower ends and lateral ends of the substrates. The second holder is disposed in a position for holding the substrates at the lower ends of the substrates, or in a position opposed to the first holder across the lower ends for holding the substrates between the lower ends and lateral ends of the substrates. The substrate fall preventing stand being disposed opposite the first holder across the lower ends of the substrates and above the second holder.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (1) Field of the Invention  
           [0002]    This invention relates to a substrate holding apparatus for holding substantially circular substrates such as semiconductor wafers.  
           [0003]    (2) Description of the Related Art  
           [0004]    A conventional example of such apparatus is shown in FIG. 1. FIG. 1 is a front view showing a principal portion of a substrate holding apparatus known in the art.  
           [0005]    The apparatus includes a first holder  101  and a second holder  102  for holding wafers W in positions between lower ends and lateral ends thereof. These holders  101  and  102  are in contact with edges of the wafers W. Further, a fall preventing stand  103  is disposed between the holders  101  and  102  for preventing the wafers W from falling in a direction perpendicular to the plane of FIG. 1. The stand  103  is out of contact with the wafers W.  
           [0006]    This substrate holding apparatus is immersed with the wafers W in a treating solution stored in a treating tub, for example. After a predetermined time of treatment, the treating solution is replaced by deionized water for cleaning treatment.  
           [0007]    The conventional apparatus with the above construction has the following drawback.  
           [0008]    When the conventional substrate holding apparatus is used in treating the wafers W in an etching or cleaning process, for example, the wafers W undergo stress which could damage circuits such as LSIs formed on the wafers W. Thus, the treatment of wafers W by using the conventional substrate holding apparatus may result in a reduced yield.  
         SUMMARY OF THE INVENTION  
         [0009]    This invention has been made having regard to the state of the art noted above, and its object is to provide a substrate holding apparatus that can relieve the stress applied to substrates, thereby avoiding a reduced yield.  
           [0010]    The above object is fulfilled, according to this invention, by a substrate holding apparatus for holding substrates in vertical posture, comprising a first holder, a second holder and a substrate fall preventing stand arranged along edges of the substrates and located below centers of the substrates, the first holder being disposed in a position for holding the substrates between lower ends and lateral ends of the substrates, the second holder being disposed in a position for holding the substrates at the lower ends of the substrates, or in a position opposed to the first holder across the lower ends for holding the substrates between the lower ends and lateral ends of the substrates, the substrate fall preventing stand being disposed opposite the first holder across the lower ends of the substrates and above the second holder.  
           [0011]    The first holder, second holder and substrate fall preventing stand are located below the centers of the substrates. Further, the first holder contacting edges of the substrates is disposed between the lower ends and lateral ends of the substrates. The second holder contacting edges of the substrates is disposed at the lower ends of the substrates, or in a position opposed to the first holder across the lower ends of the substrates. Thus, the first holder and second holder have a shorter spacing therebetween circumferentially of the substrates than in the prior art. As a result, stress on the substrates resulting from expansion and contraction of the substrates may be lessened to reduce adverse influences on the circuits and the like formed on the substrates, and avoid the lowering of yield.  
           [0012]    If the first or second holder or the fall preventing stand were located above the centers of the substrates, a treating solution could flow down to form stains on the substrates when the substrates are pulled up out of the treating solution. The above construction is effective to avoid such an inconvenience since the first or second holder or the fall preventing stand is not located above the centers of substrates.  
           [0013]    Preferably, the first holder and second holder are arranged such that a straight line extending through a point of contact between an edge of each substrate and the first holder and a point of contact between an edge of the substrate and the second holder and a tangent to the substrate in the second holder form an angle in a range of 25 to 40 degrees outwardly of the substrate.  
           [0014]    Where a straight line extending through the point of contact between an edge of each substrate and the first holder and the point of contact between an edge of the substrate and the second holder and a tangent to the substrate in the second holder form an angle in a range of 25 to 40 degrees outwardly of the substrate, friction occurring at the edges of the substrates in the first and second holders in time of expansion or contraction of the substrates is smaller than in the prior art. This lessens the stress acting radially of the substrates.  
           [0015]    An angle smaller than 25 degrees renders the holding of the substrates unstable. An angle larger than 40 degrees causes adverse influences of stress on the substrates. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.  
         [0017]    [0017]FIG. 1 is a fragmentary view in vertical section of a substrate holding apparatus known in the art;  
         [0018]    [0018]FIG. 2 is a perspective view showing an outline of substrate treating equipment having a substrate holding apparatus according to this invention;  
         [0019]    [0019]FIG. 3 is a perspective view showing an outline of the substrate holding apparatus according to the invention;  
         [0020]    [0020]FIG. 4 is a fragmentary view in vertical section of the substrate holding apparatus;  
         [0021]    [0021]FIG. 5 is a graph showing average values of frictional forces occurring at various angles; and  
         [0022]    [0022]FIG. 6 is a fragmentary view in vertical section of a modified substrate holding apparatus. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    A preferred embodiment of the invention will be described in detail hereinafter with reference to the drawings.  
         [0024]    [0024]FIGS. 2 through 4 show one embodiment of this invention. FIG. 2 is a perspective view showing an outline of substrate treating equipment having a substrate holding apparatus according to this invention. FIG. 3 is a perspective view showing an outline of the substrate holding apparatus. FIG. 4 is a fragmentary view in vertical section of the substrate holding apparatus.  
         [0025]    The substrate treating equipment having substrate holding apparatus  1  in this embodiment is exemplified by what is shown in FIG. 2. This substrate treating equipment is constructed for cleaning wafers W. A front panel  3  shown in a far end defines an opening  5  for loading and unloading wafers W. A plurality of treating units are arranged in a row opposite the wafer loading/unloading opening  5 .  
         [0026]    For example, a first cleaning unit  7  is disposed adjacent the end (left-hand side in FIG. 2) remote from the front panel  3 , a second cleaning unit  9  is disposed next, and then a third cleaning unit  11 . Each cleaning units  7 ,  9  or  11  includes a transport mechanism  7   a,    9   a  or  11   a  for moving a plurality of wafers W between its own treating tubs. Each transport mechanism  7   a,    9   a  or  11   a  is vertically and horizontally movable independently of the other transport mechanisms. A main transport mechanism  13  is disposed next to the third cleaning unit  11  for transporting one lot of wafers W to each of the cleaning units  7 ,  9  and  11 .  
         [0027]    Each transport mechanism  7   a,    9   a  or  11   a  has the substrate holding apparatus  1 . As shown in FIG. 3, the substrate holding apparatus  1  is attached to a base member  15  of transport mechanism  7   a,    9   a  or  11   a . The base member  15  is in the form of a plate sized for immersing the wafers W in each unit. The base member  15  has a first holder  17 , a second holder  19  and a substrate fall preventing stand  21  attached thereto and arranged adjacent the treating tubs. These holders  17  and  19  and stand  21  are in the form of square bars and are fixed to one another at forward ends thereof by a connecting member  23 .  
         [0028]    As shown in FIG. 4, the first holder  17 , second holder  19  and fall preventing stand  21  are arranged below the centers of wafers W. Each of the first holder  17  and second holder  19  defines a plurality of contact/support portions  17   a  or  19   a  in the form of grooves for contacting edges of wafers W. These contact/support portions  17   a  or  19   a  are arranged at predetermined intervals for holding a plurality of wafers W. The contact/support portions  17   a  and  19   a  have a groove width larger than the thickness of wafers W.  
         [0029]    The contact/support portions  17   a  have straight slopes extending rightward and downward for contacting and supporting the wafers W at obliquely downward edges thereof. The contact/support portions  19   a  have substantially horizontal surfaces for contacting and supporting the wafers W at lower ends thereof. These slopes and surfaces may be arcuate surfaces facing upward.  
         [0030]    The above contact/support portions  17   a  and  19   a  may be replaced by contact/support portions having a V-shaped cross section as seen from the edges of wafers W.  
         [0031]    The substrate fall preventing stand  21  is disposed at the same height as the first holder  17  in the vertical direction of wafers W, and defines a plurality of fall preventing grooves  21   a  arranged at the predetermined intervals for receiving and preventing fall of wafers W. The fall preventing grooves  21   a  have slopes  21   b  formed in positions out of contact with the edges of wafers W. The fall preventing grooves  21   a  are smaller in width in plan view than the contact/support portions  17   a  and  19   a  and slightly larger than the wafers W. Side surfaces of the fall preventing grooves  21   a  contact the front surfaces or back surfaces of wafers W to prevent fall of wafers W.  
         [0032]    A first straight line L 1  (two-dot chain line in FIG. 4) extending through a point of contact between the edge of wafer W and the first holder  17  and a point of contact between the edge of wafer W and the second holder  19 , and a tangent L 2  (dotted line in FIG. 4) to the wafer W in the second holder  19 , form an angle A 1  outwardly of the wafer W. This angle A 1 , preferably, is in a range of 25 to 40 degrees for the following reasons.  
         [0033]    The graph in FIG. 5 shows variations in the average of static friction in the holders  17  and  19  derived from various angles A 1  set for wafers W 200 mm in diameter (8 inch in diameter) and the wafers W 300 mm in diameter (12 inch in diameter). The variations are shown in ratios, with angle A 1 =52 degrees set for the wafers W 200 mm in diameter as a reference, and angle A 1 =52.5 degrees for the wafers W 300 mm in diameter as a reference.  
         [0034]    As seen from this graph, the ratio decreases with the angle A 1 . That is, the smaller the angle A 1  is, the smaller is the static friction in the first and second holders  17  and  19 . Thus, stress acting on wafers W by expansion and contraction may be restrained.  
         [0035]    The angle A 1  has limits imposed by construction. An angle A 1  smaller than 25 degrees renders the holding of wafers W unstable. An angle A 1  larger than 40 degrees causes adverse influences of stress acting on wafers W. A preferred angle A 1  is about 30 degrees. With this angle A 1 , wafers W may be held stably while diminishing stress. It is to be noted that an angle A 2  in the conventional example shown in FIG. 1 is about 45 degrees or larger.  
         [0036]    As noted hereinbefore, the first holder  17 , second holder  19  and fall preventing stand  21  are located below the centers of wafers W. Further, the first holder  17  in contact with the edges of wafers W is disposed between the lower ends and lateral ends of wafers W. The second holder  19  in contact with the edges of wafers W is disposed at the lower ends of wafers W. Thus, the first holder  17  and second holder  19  have a shorter spacing therebetween circumferentially of wafers W than in the prior art, thereby reducing friction produced at the edges of wafers W. As a result, adverse influences of stress on the wafers W resulting from expansion and contraction of wafers W may be reduced to avoid the lowering of yield.  
         [0037]    If the first or second holder  17  or  19  or the fall preventing stand  21  were located above the centers of wafers W, the treating solution could flow down to form stains on the wafers W when the wafers W are pulled up out of the treating solution. The construction according to the invention is effective to avoid such an inconvenience since the first or second holder  17  or  19  or the fall preventing stand  21  is not located above the centers of wafers W.  
         [0038]    &lt;Modification&gt; 
         [0039]    A modification will be described next with reference to FIG. 6. FIG. 6 is a fragmentary view in vertical section of a modified substrate holding apparatus.  
         [0040]    In the foregoing embodiment, the first holder  17  and fall preventing stand  21  are arranged at the same height with respect to the wafers W. The second holder  19  is located at the lower ends of wafers W. However, this invention is not limited to the foregoing embodiment.  
         [0041]    In the modification, the first holder  17  and second holder  19  are arranged in bilaterally symmetrical positions with respect to the lower ends of wafers W. The substrate fall preventing stand  21  is disposed above the second holder  19 . Of course, the first holder  17 , second holder  19  and fall preventing stand  21  are all arranged below the centers of wafers W.  
         [0042]    A first straight line L 1  (two-dot chain line in FIG. 6) extending through a point of contact between the edge of wafer W and the first holder  17  and a point of contact between the edge of wafer W and the second holder  19 , and a tangent L 2  (dotted line in FIG. 6) to the wafer W in the second holder  19 , form an angle A 1  outwardly of the wafer W. This angle A 1 , preferably, is in the range of 25 to 40 degrees for the reasons noted hereinbefore.  
         [0043]    In the above embodiment and modification, the first holder  17 , second holder  19  and fall preventing stand  21  are in the form of square bars. This invention is not limited to such a configuration, but may use bars of circular cross section instead.  
         [0044]    The substrate holding apparatus according to this invention may be used also in various substrate treating equipment other than the substrate treating equipment constructed for substrate cleaning treatment.  
         [0045]    This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.