Abstract:
A CSP type semiconductor device protects a circuit from the influences exerted by an external light on a circuit. In the CSP type semiconductor device, a light-shielding material, such as a silicone-based resin, an epoxy-based resin, or a metal, is deposited onto a side surface or a rear surface of a semiconductor chip where no circuit is formed.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a chip size package (CSP) type semiconductor device and a method of fabrication of the same. 
   2. Description of the Related Art 
   There are CSP type semiconductor devices designed to achieve a reduced size. In the CSP type semiconductor device, only the surface with a circuit formed thereon of a semiconductor chip is sealed with a resin, and electrodes are installed on the resin-sealed surface. Conventionally, the CSP type semiconductor devices are fabricated by first resin-sealing the circuit-mounted surface of a semiconductor wafer on which a circuit has been formed, then by dicing the semiconductor wafer into individual semiconductor devices. 
   In the conventional CSP type semiconductor devices, however, the rear surfaces and side surfaces of the semiconductor chips thereof where no circuit has been formed are exposed. This causes light to enter the semiconductor chips through the rear surfaces or side surfaces of the semiconductor chips if the semiconductor chips are mounted in, for example, transparent skeleton type modules. There have been some cases where the light that has entered the semiconductor chip acts on the circuit, adversely affecting the operation of the circuit formed on the semiconductor chip. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a semiconductor device and a method of fabrication of the same that permit the problem mentioned above to be solved. 
   To this end, according to one aspect of the present invention, there is provided a semiconductor device including a semiconductor chip having a surface with a circuit formed thereon, a side surface, and a rear surface, and a metal film for blocking light, wherein the metal film covers the side surface and the rear surface of the semiconductor chip. 
   According to another aspect of the present invention, there is provided a method of fabrication of a semiconductor device including a step for resting a semiconductor wafer having a surface with a circuit formed thereon, a side surface, and a rear surface on a pedestal, such that the surface with the circuit formed thereon opposes the pedestal, a step for cutting the semiconductor wafer, and a step for attaching a light-shielding material to the side surface and the rear surface of the semiconductor wafer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are sectional views showing a first embodiment of the present invention; 
       FIGS. 2A through 2F  are sectional views showing a second embodiment of the present invention; and 
       FIGS. 3A through 3G  are sectional views showing a third embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (First Embodiment) 
     FIG. 1  provides sectional views showing a first embodiment of the present invention. The first embodiment will be described in conjunction with  FIGS. 1A and 1B . 
   Referring to  FIG. 1A , the semiconductor device according to the present invention is constructed of a semiconductor chip  110  and a metal film  120  for blocking light. The semiconductor chip  110  has a front surface, a side surface, and a rear surface. There is a circuit (not shown) formed on the front surface of the semiconductor chip, and the circuit is sealed with an opaque resin  130  for blocking light. Furthermore, metal bumps  140  electrically connected with the circuit are formed on the front surface of the semiconductor chip  110  through the intermediary of the resin  130 . 
   The metal film  120  covers the entire rear surface and side surface of the semiconductor chip  110 . The metal film  120  is formed of two layers, the layer adjacent to the semiconductor chip  110  being made of a Ti layer or a Ni layer having a thickness of 40 nm or more. A layer made of Au that has a thickness of 200 nm or more covers the Ti layer or the Ni layer. 
   The first embodiment of the present invention has the aforesaid structure, so that the rear surface and the side surface of the semiconductor chip  110  are covered with the metal film  120 . The metal film  120  efficiently blocks light attempting to enter into the semiconductor device from outside, thus preventing the light from entering into the semiconductor chip  110 . Thus, the influences of the light on the circuit can be controlled. In particular, according to the present invention, the entire rear surface of the semiconductor chip  110  that has a relatively large area is covered by the metal film  120 ; therefore, the combination of the metal film  120  and the sealing resin  130  covers all the surfaces of the semiconductor chip  110 . With this arrangement, it is possible to shield the semiconductor device from virtually all light coming from any directions. 
   In place of the metal film  120 , an epoxy-based resin film or a silicone-based resin film may be used to cover the semiconductor chip  110 . In this case, the epoxy-based resin film or the silicone-based resin film should be capable of blocking light trying to enter into the semiconductor device from outside. The light blocking effect of the films is enhanced especially by adding a pigment, such as carbon, to the epoxy-based resin film or the silicone-based resin film, making it further effective for preventing external light from entering into the semiconductor chip  110 . 
   The relationship between the metal film  120  and the resin  130  may alternatively be the one shown in  FIG. 1B  to obtain the same advantage as that obtained by the one shown in  FIG. 1A . 
   (Second Embodiment) 
     FIG. 2  provides sectional views showing a second embodiment of the present invention. The second embodiment of the invention will be described in conjunction with  FIG. 2 . The second embodiment of the invention is a method for fabricating the semiconductor device shown in  FIG. 1A  in the first embodiment of the invention. 
   Firstly, the surface with a circuit (not shown) formed thereon of a semiconductor wafer  210  having the circuit formed on the front surface thereof is sealed with a resin  230 , as shown in  FIG. 2A . 
   Secondly, metal bumps  240  electrically connected to the circuit formed on the front surface of a semiconductor wafer  210  are formed on the front surface of the semiconductor wafer  210  through the intermediary of the resin  230 , as shown in  FIG. 2B . At this time, the metal bumps  240  are not formed around the semiconductor wafer  210 . 
   Thirdly, the semiconductor wafer  210  is rested on a pedestal  250  such that the front surface of the semiconductor wafer  210  opposes the pedestal  250 , as shown in  FIG. 2C . At this time, an adhesive tape  260 , such as an electron tape, is provided on the pedestal  250  to fix the semiconductor wafer  210  to the pedestal  250 . 
   Fourthly, the semiconductor wafer  210  as well as the resin  230  is cut by using a dicing saw  270  to divide the semiconductor wafer  210  into semiconductor chips  211 , as shown in  FIG. 2D . 
   Lastly, an epoxy-based resin or a silicone-based resin  280  is sprayed onto the rear surfaces and the side surfaces of the semiconductor chips  211 , as shown in  FIG. 2E . 
   As shown in  FIG. 2F , a metal film  220  may be formed by vapor deposition in place of spraying the epoxy-based resin or silicone-based resin  280 . The vapor deposition of the metal film  220  is advantageous over the spraying of the epoxy-based resin or silicone-based resin  280  in that the film can be formed to have uniform thickness. 
   According to the second embodiment of the present invention, the semiconductor wafer  210  is cut on the pedestal  250 , so that after the semiconductor wafer  210  is diced into the semiconductor chips  211 , the epoxy-based resin or the silicone-based resin  280  is sprayed onto all the semiconductor chips  211  at a time. This permits a simplified fabrication process to be achieved. 
   (Third Embodiment) 
     FIG. 3  provides sectional views showing a third embodiment of the present invention. The third embodiment of the invention will be described in conjunction with  FIG. 3 . The third embodiment of the invention is a method for fabricating the semiconductor device shown in  FIG. 1B  in the first embodiment of the invention. 
   Firstly, the surface with a circuit (not shown) formed thereon of a semiconductor wafer  310  having the circuit formed on the front surface thereof is sealed with a resin  330 , as shown in  FIG. 3A . 
   Secondly, metal bumps  340  electrically connected to the circuit formed on the front surface of a semiconductor wafer  310  are formed on the front surface of the semiconductor wafer  310  through the intermediary of the resin  330 , as shown in  FIG. 3B . At this time, the metal bumps  340  are not formed around the semiconductor wafer  310 . 
   Thirdly, the semiconductor wafer  310  is rested on a pedestal  350  such that the front surface of the semiconductor wafer  310  opposes the pedestal  350 , as shown in  FIG. 3C . At this time, an adhesive tape  360 , such as an electron tape, is provided on the pedestal  350  to fix the semiconductor wafer  310  to the pedestal  350 . The steps up to this point are the same as those of the second embodiment. 
   Fourthly, only the semiconductor wafer  310  is cut by using a dicing saw  370 . At this time, the resin  330  is not cut, as shown in  FIG. 3D . 
   Fifthly, an epoxy-based resin or a silicone-based resin  380  is sprayed onto the rear surface and the side surface of the semiconductor wafer  310 , as shown in  FIG. 3E . 
   Alternatively, the metal film  320  may be formed by vapor deposition rather than spraying the epoxy-based resin or the silicone-based resin  380 , as shown in  FIG. 3F . The vapor deposition of the metal film  320  is advantageous over the spraying of the epoxy-based resin or silicone-based resin  380  in that the film can be formed to have uniform thickness. 
   Although not shown, instead of spraying the epoxy-based resin or the silicone-based resin  380 , only the semiconductor wafer  310  may be immersed, while the semiconductor wafer  310  being fixed to the adhesive tape  360 , in an epoxy-based resin or a silicone-based resin thereby to make the epoxy-based resin or the silicone-based resin  380  adhere to the semiconductor wafer  310  after dicing only the semiconductor wafer  310 . 
   Lastly, the resin  330  is cut by using the dicing saw  370  again to completely divide the semiconductor wafer  310  into semiconductor chips  311 , as shown in  FIG. 3G . 
   The third embodiment of the present invention provides the same advantage as that of the second embodiment. 
   According to the third embodiment of the invention, when the epoxy-based resin or the silicone-based resin  380  is deposited onto the semiconductor wafer  310 , the resin  330  formed on the front surface of the semiconductor wafer  310  has not yet been cut. In other words, at this point, the interface between the adhesive tape  360  and the resin  330  is not yet exposed. Hence, when an epoxy-based resin or a silicone-based resin  380  is deposited by immersion, the adherence of the epoxy-based resin or the silicone-based resin  380  to the metal bumps  340  through the interface between the adhesive tape  360  and the resin  330  can be minimized. 
   As described above, according to the present invention, the rear surface and the side surface of a semiconductor chip are covered by a metal film, an epoxy-based resin, or a silicone-based resin to prevent external light from entering into a semiconductor chip. This arrangement advantageously controls the influences of light on a circuit formed on the semiconductor chip. Moreover, to fabricate semiconductor chips, a metal film, an epoxy-based resin, or a silicone-based resin is deposited onto all semiconductor chips at a time, permitting a simplified fabricating process to be achieved.