Abstract:
A die seal ring disposed in a die and surrounding an integrated circuit region of the die is described. The die seal ring has at least two different local widths.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a wafer structure, and more particularly relates to a die seal ring that can effectively prevent a die from being damaged by the stress caused by sawing of the die and to a wafer wherein each die has such a die seal ring. 
         [0003]    2. Description of Related Art 
         [0004]    Along with the development in technology, integrated circuit devices have been widely applied in our daily life. Manufacture of an IC device generally includes three stages, production of a semiconductor wafer, fabrication of integrated circuits on the dies on the wafer and packaging of the dies cut from the wafer. The first step in the packaging stage is to cut the dies from the wafer. 
         [0005]    A semiconductor wafer has a plurality of perpendicularly crossing scribe lines to separate a plurality of dies. After integrated circuits are formed on the dies, a diamond blade can be used to saw the wafer along the scribe lines to obtain single dies. Since various material layers are formed on the wafer, the stress caused by blade sawing easily causes damages like chipping and peeling to the dies, especially when there is a low-k material formed on the dies. Thus, the device reliability is lowered. 
         [0006]    Another way to cut the dies is laser grooving, which still has certain problems however. For example, when a metal material has been formed on the wafer, the metal is difficult to remove completely by laser and forms debris that contaminates the dies. Moreover, a heat effect area is formed beside the scribe lines lowering the reliability of the dies. In addition, the price of a laser cutting system is 2-3 time higher than that of a diamond blade cutting system, so that the manufacturing cost is much increased. 
         [0007]    Some methods capable of preventing damages like chipping and peeling of the die in the sawing have been provided. For example, as shown in  FIG. 1 , U.S. Pat. No. 6,876,062 teaches a structure  100  formed at a die corner and including an irregular seal ring  102  and a dummy pattern  103  to prevent the die from being damaged by the stress, wherein the dummy pattern  103  may be formed at both sides of the seal ring  102 . 
         [0008]    Though the above structure  100  effectively prevents the die from being damaged by the stress caused by sawing, the fabricating process adversely gets more complicated. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, this invention provides a die seal ring that can effectively prevent a die from being damaged by the stress caused by sawing of the die. 
         [0010]    This invention also provides a wafer that allows the dies sawn therefrom to have higher reliability. 
         [0011]    The die seal ring of this invention is disposed in a die and surrounds an integrated circuit region of the die, having at least two different local widths. 
         [0012]    In certain embodiments, the die is subjected to different stresses at different portions thereof as being sawn from a wafer, wherein the local width of the die seal ring at a portion of the die substantially increase with an increase in the stress thereat. In an embodiment, the different stresses include a first stress and a second stress higher than the first stress, the at least two different local widths include a first width and a second width larger than the first width, the first width is at a portion of the die subjected to the first stress, and the second width is at a portion of the die subjected to the second stress. In another embodiment, the different stresses include, from low to high, a first stress, a second stress and a third stress, the at least two different local widths include, from small to large, a first width, a second width and a third width, the first width is at a portion of the die subjected to the first stress, the second width at a portion of the die subjected to the second stress and the third width at a portion of the die subjected to the third stress. 
         [0013]    The wafer of this invention includes a plurality of dies separated by a plurality of scribe lines, wherein each die includes an integrated circuit region and a die seal ring surrounding the integrated circuit region, and the die seal ring has at least two different local widths. 
         [0014]    In an embodiment, each die is subjected to different stresses at different portions thereof as being sawn from the wafer, and the local width of the die seal ring at a portion of the die substantially increase with an increase in the stress thereat. The die seal ring may include a metal. 
         [0015]    In embodiments where the local width of the die seal ring at a portion of the die substantially increase with an increase in the stress thereat, a larger local width of the die seal ring can effectively prevent the die from being damaged by a higher stress thereat. Therefore, the die sawn from the wafer can have higher reliability. 
         [0016]    In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  illustrates a top view of a structure for preventing damages to a die in the prior art. 
           [0018]      FIG. 2  illustrates a local top view of a wafer with die seal rings according to an embodiment of this invention. 
           [0019]      FIG. 3  illustrates a local top view of a wafer with die seal rings according to another embodiment of this invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    It is noted that the following embodiments are intended to further explain this invention but not to limit the scope of this invention. 
         [0021]      FIG. 2  illustrates a local top view of a wafer with die seal rings according to an embodiment of this invention. The wafer  200  includes a plurality of dies  202  that are separated by a plurality of scribe lines  204 , wherein each die  202  includes an integrated circuit (IC) region  206  and a die seal ring  208  surrounding the IC region  206 . The material of the die seal ring  208  may be a metal like copper. 
         [0022]    In this embodiment, the die seal ring  208  has an octangular shape and includes long segments  208   a ,  208   c ,  208   e  and  208   g  and short segments  208   b ,  208   d ,  208   f  and  208   h . The long segments  208   a  to  208   g  have substantially the same width W 1 . The short segments  208   b  to  208   h  have substantially the same width W 2  (&gt;W 1 ). 
         [0023]    The local widths W 1  and W 2  of the die seal ring  208  are designed according to the stress distribution in the die  202  as being sawn from the wafer  200 . When the die  202  is being sawn from the wafer  200 , the stress S 2  at a portion of the die  202  around a short segment  208   b ,  208   d ,  208   f  or  208   h  is higher than the stress S 1  at a portion of the die  202  around a long segment  208   a ,  208   c ,  208   e  or  208   g . The width W 2  of the short segments  208   b ,  208   d ,  208   f  and  208   h  is larger than that (W 1 ) of the long segments  208   a ,  208   c ,  208   e  and  208   g  to sustain the higher stress, so that the die  202  can be effectively prevented from being damaged by the stresses S 1  and S 2 . Therefore, all the dies  202  sawn from the wafer  200  can have higher reliability. 
         [0024]      FIG. 3  illustrates a local top view of a wafer with die seal rings according to another embodiment of this invention. The wafer  300  includes a plurality of dies  302  that are separated by a plurality of scribe lines  304 , wherein each die  302  includes an IC region  306  and a die seal ring  308  surrounding the IC region  206 . The material of the die seal ring  308  may also be a metal like copper. 
         [0025]    In this embodiment, the die seal ring  208  has a quadrangular shape and includes four edge segments  308   a ,  308   b ,  308   c  and  308   d  and four corner segments C 1 , C 2 , C 3  and C 4 . The edge segments  308   a ,  308   b ,  308   c  and  308   d  have substantially the same width W 3 . The corner segments C 1  and C 2  have substantially the same width W 4  (&gt;W 3 ). The corner segments C 3  and C 4  have substantially the same width W 5  (&gt;W 4 ). 
         [0026]    The local widths W 3 , W 4  and W 5  of the die seal ring  308  are designed according to the stress distribution in the die  302  as being sawn from the wafer  300 . When the die  302  is being sawn from the wafer  300 , the stress S 4  at a portion of the die  302  around the corner segment C 1  or C 2  is higher than the stress S 3  at a portion of the die  302  around an edge segment  308   a ,  308   b ,  308   c  or  308   d , the stress S 5  at a portion of the die  302  around the corner segment C 3  is higher than the stress S 4 , and the stress S 6  at a portion of the die  302  around the corner segment C 4  is higher than the stress S 5 . The width W 4  of the corner segments C 1  and C 2  is larger than that (W 3 ) of the edge segments  308   a ,  308   b ,  308   c  and  308   d  to sustain higher stress, and the width W 5  of the corner segments C 3  and C 4  is larger than that (W 4 ) of the corner segments C 1  and C 2  to sustain even higher stress. It is noted that though the stress S 6  at a portion of the die  302  around the corner segment C 4  is larger than the stress S 5  at a portion of the die  302  around the corner segment C 3 , setting the same width (W 5 ) to the corner segment C 3  and C 4  is feasible when the width W 5  is sufficient for the corner segment C 4  to sustain the higher stress S 6 . 
         [0027]    It is noted that though an octangular or quadrangular die seal ring is exemplified in the above embodiments, one of ordinary skill in the art can understand, based on the above teaching, that increasing the local width of the die seal ring at a portion of the die subjected to a higher stress can prevent damages to the die more effectively. Therefore, the shape of the die seal ring in this invention are not limited to the above mentioned, but can be any other shape suitably to be formed in a die surrounding the IC region. 
         [0028]    In each of the above embodiments, since the local width of the die seal ring at a portion of the die substantially increase with an increase in the stress thereat, a larger local width of the die seal ring can effectively prevent the die from being damaged by a higher stress thereat. Hence, the die sawn from the wafer can have higher reliability. 
         [0029]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.