Abstract:
A semiconductor device according to the present invention includes: a semiconductor chip; a wiring formed on the semiconductor chip; a passivation film, coating the wiring and having an opening for partially exposing the wiring from the passivation film; an interposing film, formed on a portion of the wiring facing the opening; and a post bump, raisedly formed on the interposing film and with a peripheral edge portion thereof protruding more toward a side than a peripheral edge of the interposing film.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device applying a so-called WL-CSP (Wafer Level-Chip Size Package) technology. 
         [0003]    2. Description of Related Art 
         [0004]    With the recent making of semiconductor devices more advanced in function and multifunctional, practical use of WL-CSP technology is progressing. With a WL-CSP technology, a packaging process is completed in a wafer state, and a size of each individual chip cut out by dicing becomes a package size. 
         [0005]      FIG. 4  is a schematic sectional view of a structure of a semiconductor device to which a WL-CSP technology is applied. 
         [0006]    The semiconductor device  101  includes a semiconductor chip (not shown) making up a base thereof. An interlayer insulating film  102  made of SiO 2  (silicon oxide) is formed on the semiconductor chip. A wiring  103  made of Al (aluminum) is formed in a predetermined wiring pattern on the interlayer insulating film  102 . A passivation film  104  made of SiN (silicon nitride) is formed on the interlayer insulating film  102  and the wiring  103 . An opening  105  for exposing a portion of the wiring  103  from the passivation film  104  is formed in the passivation film  104 . 
         [0007]    A barrier film  106  made of Ti (titanium) is formed on a portion of the wiring  103  facing the opening  105 . A peripheral edge portion of the barrier film  106  rides on the passivation film  104 . A post bump  107  made of Cu (copper) is formed on the barrier film  106 . A side surface of the post bump  107  is flush with a side surface of the barrier film  106 . A solder ball  108  is formed on the post bump  107 . The solder ball  108  is an external terminal connected to an external wiring on a wiring substrate. By the solder ball  108  being connected to the external wiring on the wiring substrate, electrical connection of the wiring  103  and the external wiring is achieved and the semiconductor device  101  is supported on the wiring substrate. 
         [0008]    With such a structure, when an external force is applied to the solder ball  108 , stress concentrates at the peripheral edge portion of the barrier film  106  and the post bump  107 . By the concentration of stress, a crack may form in the passivation film  104  positioned immediately below the peripheral edge portion of the barrier film  106 . 
         [0009]    To prevent crack formation in the passivation film  104 , forming of a polyimide layer having a penetrating hole in communication with the opening  105  on the passivation film  104  and positioning of the peripheral edge portion of the barrier film  106  on the polyimide layer may be considered. Because the polyimide layer is interposed between the peripheral edge portion of the barrier film  106  and the passivation film  104 , even when stress concentrates at the peripheral edge portions of the barrier film  106  and the post bump  107 , the stress is absorbed by the polyimide layer and is not transmitted to the passivation film  104 . Crack formation in the passivation film  104  can thus be prevented. 
         [0010]    However, because a step of forming the polyimide layer must be added, a number of manufacturing steps of the semiconductor device  101  is increased and this causes increase in manufacturing cost. Also, the polyimide layer must be formed to an adequate thickness capable of absorbing the stress. Thus, there is an issue of increase in thickness of the semiconductor device  101 . 
       SUMMARY OF THE INVENTION 
       [0011]    An object of the present invention is to provide a semiconductor device with which crack formation in a passivation film can be prevented without causing increase in number of manufacturing steps, increase in thickness and other problems. 
         [0012]    A semiconductor device according to one aspect of the present invention includes: a semiconductor chip; a wiring formed on the semiconductor chip; a passivation film, coating the wiring and having an opening for partially exposing the wiring from the passivation film; an interposing film, formed on a portion of the wiring facing the opening; and a post bump, raisedly formed on the interposing film and with a peripheral edge portion thereof protruding more toward a side than a peripheral edge of the interposing film. 
         [0013]    With this configuration, the wiring is formed on the semiconductor chip. The wiring is coated with the passivation film. The opening for partially exposing the wiring from the passivation film is formed in the passivation film. The interposing film is formed on the portion of the wiring facing the opening. The protuberant post bump, with its peripheral edge portion protruding more toward the side than the peripheral edge portion of the interposing film, is formed on the interposing film. 
         [0014]    By the peripheral edge portion of the post bump protruding more toward the side than the peripheral edge of the interposing film, a space is formed between the peripheral edge portion of the post bump and the passivation film. By this space being present, the peripheral edge portion of the post bump is deformable in a direction of opposing the passivation film. Thus, even if a stress arises in the post bump, the stress can be absorbed by deformation of the peripheral edge portion of the post bump. Consequently, crack formation in the passivation film can be prevented. 
         [0015]    Further, because a polyimide layer for stress relaxation is not interposed between the passivation film and the post bump, problems due to providing a polyimide layer, such as increase in number of manufacturing steps, increase in thickness of the semiconductor device, etc., do not occur. 
         [0016]    Preferably, a protrusion amount of the peripheral edge portion of the post bump with respect to the peripheral edge of the interposing film is greater than a thickness of the interposing film. By the protrusion amount of the peripheral edge portion of the post bump thus being greater than the thickness of the interposing film, a width of the deformable peripheral edge portion of the post bump can be secured to be greater than the thickness of the interposing film. 
         [0017]    To make the protrusion amount of the peripheral edge portion of the post bump greater than the film thickness of the interposing film, for example, a layer made of a material of the interposing film is formed on the passivation film and on the wiring, and after forming the post bump on this layer, in a step of patterning the layer made of the material of the interposing film by wet etching, an etching time is set so that etching progresses to below the post bump. 
         [0018]    Further, a peripheral edge portion of the interposing film may be formed to ride on a circumference of the opening in the passivation film. 
         [0019]    The foregoing and other objects, features, and effects of the present invention will become more apparent from the following detailed description of the embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a side view of an outer appearance of a semiconductor device according to an embodiment of the present invention. 
           [0021]      FIG. 2  is a schematic sectional view of a structure of a portion of the semiconductor device shown in  FIG. 1 . 
           [0022]      FIG. 3A  is a schematic sectional view for describing a method for manufacturing the semiconductor device shown in  FIG. 2 . 
           [0023]      FIG. 3B  is a schematic sectional view of a step subsequent to that of  FIG. 3A . 
           [0024]      FIG. 3C  is a schematic sectional view of a step subsequent to that of  FIG. 3B . 
           [0025]      FIG. 3D  is a schematic sectional view of a step subsequent to that of  FIG. 3C . 
           [0026]      FIG. 3E  is a schematic sectional view of a step subsequent to that of  FIG. 3D . 
           [0027]      FIG. 4  is a schematic sectional view of a structure of a conventional semiconductor device. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    An embodiment of the present invention shall now be described in detail with reference to the attached drawings. 
         [0029]      FIG. 1  is a side view of an outer appearance of a semiconductor device according to a first embodiment of the present invention. 
         [0030]    A WL-CSP technology is applied in the semiconductor device  1 . The semiconductor device  1  includes a semiconductor chip  2 , a plurality of post bumps  3  disposed on the semiconductor chip  2 , and solder balls  4  bonded to the respective post bumps  3 . 
         [0031]      FIG. 2  is a schematic sectional view of a structure of a portion surrounded by a broken line A in  FIG. 1 . 
         [0032]    An interlayer insulating film  5  made of SiO 2  is formed on a top layer portion of the semiconductor chip  2 . A wiring  6  made of Al is formed in a predetermined pattern on the interlayer insulating film  5 . 
         [0033]    A passivation film  7  made of SiN is formed on the interlayer insulating film  5  and the wiring  6 . The wiring  6  is covered by the passivation film  7 . An opening  8  for exposing a portion of the wiring  6  from the passivation film  7  is formed in the passivation film  7 . 
         [0034]    A barrier film  9  made of TiW (titanium tungsten) is coated on a portion of the wiring  6  facing the opening  8 . The barrier film  9  has a predetermined thickness T (for example of 180 nm). The barrier film  9  covers a top surface of the wiring  6  and a side surface of the passivation film  7  inside the opening  8  and a peripheral edge portion thereof rides on a top surface of the passivation film  7 . 
         [0035]    A seed film  10  made of Cu is formed on the barrier film  9 . A peripheral edge portion of the seed film  10  protrudes to a side with respect to a peripheral edge of the barrier film  9  by a protrusion amount D greater than the film thickness T of the barrier film  9 . 
         [0036]    The post bump  3  is protuberantly formed on the seed film  10 . The post bump  3  is made, for example, of Cu. A side surface of the post bump  3  is substantially flush with a side surface of the seed film  10 . 
         [0037]    By a peripheral edge portion of the post bump  3  protruding more to the side than the peripheral edge of the barrier film  9 , a space is formed between the peripheral edge portion of the post bump  3  and the passivation film  7 . By the presence of this space, the peripheral edge portion of the post bump  3  is deformable in a direction of opposing the passivation film  7 . Thus, even if a stress arises in the post bump  3 , the stress can be absorbed by deformation of the peripheral edge portion of the post bump  3 . Consequently, crack formation in the passivation film  7  can be prevented. 
         [0038]    Also, because a polyimide layer for stress relaxation is not interposed between the passivation film  7  and the post bump  3 , problems due to providing a polyimide layer, such as increase in number of manufacturing steps of the semiconductor device  1 , increase in thickness of the semiconductor device  1 , etc., do not occur. 
         [0039]    The protrusion amount D of the peripheral edge portion of the post bump  3  is greater than the thickness T of the barrier film  9 . A width of the deformable peripheral edge portion in the post bump  3  can thereby be secured to be greater than the thickness of the barrier film  9 . 
         [0040]      FIGS. 3A to 3E  are schematic sectional views illustrating, in order of process, a method for manufacturing the semiconductor device shown in  FIG. 2 . 
         [0041]    First, as shown in  FIG. 3A , the interlayer insulating film  5  is formed by a CVD (Chemical Vapor Deposition) method. Thereafter, by a sputter method, a metal film made of Al (not shown) is formed on the entire surface of the interlayer insulating film  5 . Then, the metal film on the interlayer insulating film  5  is removed selectively by photolithography and etching. The wiring  6  having the predetermined pattern is thereby formed on the interlayer insulating film  5 . 
         [0042]    Then, as shown in  FIG. 3B , the passivation film  7  is formed on the interlayer insulating film  5  and the wiring  6  by the CVD method. Thereafter, a resist pattern (not shown) is formed on the passivation film  7 . Then, the passivation film  7  is etched using the resist pattern as a mask. The opening  8  exposing a portion of the wiring  6  from the passivation film  7  is thereby formed in the passivation film  7 . After the opening  8  is formed, the resist pattern is removed. 
         [0043]    Thereafter, as shown in  FIG. 3C , the barrier film  9  made of TiW is formed on the portion of the wiring  6  facing the opening  8  and on the passivation film  7  by the sputter method. Then, the seed film  10  made of Cu is formed on the barrier film  9  by the sputter method. Then, a resist film  12  having an opening  11  at a portion at which the post bump  3  is to be formed is formed on the seed film  10 . Thereafter, Cu is deposited inside the opening  11  of the resist film  12  by a plating method and the post bump  3  is thereby formed. After the post bump  3  is formed, the resist film  12  is removed. 
         [0044]    Then, as shown in  FIG. 3D , a portion of the seed film  10  exposed from the post bump  3  is removed by wet etching. That is, a liquid capable of etching the seed film  10  is supplied to the seed film  10  and the seed film  10  is removed with the exception of a portion in contact with the post bump  3 . Thus, the seed film  10  having the side surface substantially flush with the side surface of the post bump  3  remains between the post bump  3  and the barrier film  9 . 
         [0045]    Thereafter, a liquid capable of etching the barrier film  9  is supplied to the barrier film  9 . In this process, an etching liquid supplying time is set so that the etching progresses to the barrier film  9  below the seed film  10 . A portion of the barrier film  9  exposed from the seed film  10  and a portion of the barrier film  9  sandwiched between the peripheral edge portion of the seed film  10  and the passivation film  7  are thereby removed as shown in  FIG. 3E . Consequently, the side surface of the barrier film  9  is positioned more to an inner side (the opening  8  side) than the side surface of the seed film  10 , and the post bump  3  and the seed film  10  take on shapes with the peripheral edge portions protruding to the side with respect to the peripheral edge of the barrier film  9 . 
         [0046]    By thus setting the etching time in the process of patterning the layer made of the material of the barrier film  9  so that the etching progresses below the post bump  3 , the protrusion amount D of the peripheral edge portion of the post bump  3  can be made greater than the thickness T of the barrier film  9 . A space can thereby be formed between the peripheral edge portion of the seed film  10  and the passivation film  7  without causing increase in the number of manufacturing steps. 
         [0047]    Various modifications may be applied to the present embodiment. 
         [0048]    For example, the material of the barrier film  9  may be any material having a barrier property with respect to Cu. Ti (titanium), Ta (tantalum), and TaN (tantalum nitride) can be cited as examples of such a material. 
         [0049]    Further, Au (gold) may be used as the material of the post bump  3 . When Au is employed as the material of the post bump  3 , TiW can be used as the material of the barrier film  9 . 
         [0050]    The wiring  6  may be formed using a metal material containing Cu. AlCu (aluminum/copper alloy) and Cu can be cited as examples of a metal material containing Cu. In this case, a wiring groove may be formed by digging in from an upper surface of the interlayer insulating film  5  and the wiring  6  may be embedded in this wiring groove. 
         [0051]    While the present invention has been described in detail by way of the embodiments thereof, it should be understood that these embodiments are merely illustrative of the technical principles of the present invention but not limitative of the invention. The spirit and scope of the present invention are to be limited only by the appended claims. 
         [0052]    This application corresponds to Japanese Patent Application No. 2007-298361, filed with the Japan Patent Office on Nov. 16, 2007, the disclosure of which is incorporated herein by reference.