Abstract:
A semiconductor device excellent in bonding strength of bumps with respective protruded electrodes and having high reliability wherein a wiring pattern  28  to be connected to an electrode  22  of a semiconductor chip  20  is formed on an insulting film  23  formed on the semiconductor chip  20  in which the electrode  20  is formed, protruded electrodes  32  are formed on the wiring pattern  28 , the wiring pattern  28  is covered with a protective film  36 , and a bump  38  for external connection is formed on the end portion of each of the protruded electrodes  32  exposed from the protective film  36 , the bump  38  is formed in such a manner that the bump is bonded to the at least entire end face of each of the protruded electrodes  32.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, having a chip-size package structure, and a process for producing the same. 
     2. Description of the Related Art 
     A process for producing semiconductor devices comprising assembling semiconductor devices in the wafering step has been developed (Japanese Unexamined Patent Publication (Kokai) No. 10-79362). The process can provide semiconductor devices each having a separate chip-size package structure completed by cutting, and reduce the production costs. 
     The production process comprises forming a wiring pattern (rewiring pattern), to be connected to electrodes of the semiconductor chip, on an insulating film formed on the semiconductor chip, forming protruded electrodes by plating the wiring pattern, forming a protective film covering the wiring pattern by compression molding, and forming a solder bump for external connection on the end portion of each of the protruded electrodes. 
     The step of forming a protective film comprises the following procedures. 
     That is, a top face and a bottom face are heated to about 175° C. A temporary film is absorbed by the top face. 
     A wafer on which a wiring pattern and protruded electrodes are formed is placed on the bottom face, and a sealing resin is placed on the wafer. 
     The resin is melted by the heat and pressure of the sealing mold to be spread over the entire wafer, and held within the mold to be cured. 
     The wafer is taken out of the mold, and the temporary film is peeled off. 
     A solder bump for external connection is formed on the end portion of each of the protruded electrodes. 
     However, the conventional process for producing a semiconductor device has been found to have the following problems. 
     That is, when the process is carried out by compression molding wherein a resin is placed on a wafer, the resin is melted by pressing the resin with a mold, and the molten resin is spread over the entire wafer to form a protective film, the protective film is also placed on the end face of each of the protruded electrodes, and removal of the protective film from the end face becomes incomplete. 
     Accordingly, when a solder bump  12  is bonded to the end portion of a protruded electrode  10  as shown in FIG. 16, the bond area of the solder bump  12  is reduced by a protective film  14 , and the bond strength becomes insufficient, which causes a problem in reliability. 
     Moreover, the bonded portion of the solder bump  12  makes an acute angle with the surface of the protruded electrode  12 , which causes the problem that the bump tends to be easily removed by impact. 
     In addition, the reference numerals  15 ,  16  and  18  designate a semiconductor chip, an insulating film formed from a polyimide resin and a rewiring pattern formed on the insulating film  16 , respectively. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a semiconductor device which is excellent in the bond strength of a bump with each of the protruded electrodes and which is highly reliable, and a process for producing the same. 
     In a semiconductor device according to the present invention wherein a wiring pattern to be connected to an electrode of a semiconductor chip is formed on an insulating film formed on the semiconductor chip surface on which the electrode is formed, protruded electrodes are formed on the wiring pattern, the wiring pattern is covered with a protective film, and a bump for external connection is formed on the end portion of each of the protruded electrodes exposed from the protective film, the bump is formed by bonding the bump to the at least entire end face of each of the protruded electrodes. 
     Since the bump is bonded to the entire end face of each of the protruded electrodes as described above, the bump is excellent in bond strength. 
     The bump mentioned above is characterized in that a barrier plated layer is formed on the end face of each of the protruded electrodes, and that the bump is formed in such a manner that the bump is bonded to the entire barrier plated layer. 
     Since the bump shows good wettability with the barrier plated layer, it is bonded to the entire barrier plated layer. 
     The protective film is characterized in that the protective film is formed to have a top surface lower than the position at which the bump is bonded to each of the protruded electrodes. 
     Since the top surface of the protective film is lower than that of the protruded electrodes, the protective film is never placed on the end portion of the protruded electrodes, and the bump is bonded to the entire end face of each of the protruded electrodes. 
     The protruded electrodes are appropriate when an oxide film is formed on the peripheral surface of each of the protruded electrodes, and when there is a gap between the protective film and the peripheral surface of each of the protruded electrodes. 
     The protruded electrodes thus become independent of the protective film, and are not influenced thereby even when the coefficient of thermal expansion of the electrodes differs from that of the film. Stress concentration between the protruded electrode and the bump is therefore relaxed, and crack formation and the like, in the bump and in the protective film, can be suppressed. 
     Furthermore, it is also appropriate in this case to form the protective film in such a manner that the level of the protective film becomes higher than the position at which the bump is bonded to each of the protruded electrodes, and that part of the peripheral surface of the bump is contacted with the protective film. 
     As a result, a gap between each of the electrodes and the protective film can be closed, and invasion of moisture, etc. can be prevented. 
     Next, in a process for producing a semiconductor device according to the present invention wherein a wiring pattern to be connected to an electrode of a semiconductor chip is formed on an insulating film formed on the semiconductor chip surface on which the electrode is formed, protruded electrodes are formed on the wiring pattern, the wiring pattern is covered with a protective film, and a bump for external connection is formed on the end portion of each of the protruded electrodes exposed from the protective film, the process comprises the steps of: covering the wiring pattern formed on the insulating film with a resist layer, and forming holes in the resist layer to expose part of the wiring pattern; plating the wiring pattern within the holes to form the protruded electrodes; removing the resist layer; effecting sealing by supplying a resin to the wiring pattern to form a resin layer having a top surface lower than that of the protruded electrodes, thereby forming a protective film; and forming a bump on each of the protruded electrodes in such a manner that the bump is bonded to the at least entire end face of each of the protruded electrodes. 
     Since the protective film is formed by potting or spin coating to have a top surface lower than that of each of the protruded electrodes, the entire end face of each of the protruded electrodes is exposed, and a bump is bonded to the entire end face, which improves the bond strength of the bump. 
     Moreover, the process is appropriate when the process comprises plating to form a barrier plated layer on the end face of each of the protruded electrodes, and when the bump is formed in the bump-forming step in such a manner that the bump is bonded to the entire barrier plated layer. 
     Furthermore, in a process for producing a semiconductor device according to the present invention wherein a wiring pattern to be connected to an electrode of a semiconductor chip is formed on an insulating film formed on the semiconductor chip surface on which the electrode is formed, protruded electrodes are formed on the wiring pattern, the wiring pattern is covered with a protective film, and a bump for external connection is formed on the end portion of each of the protruded electrodes exposed from the protective film, the process comprises the steps of: covering the wiring pattern formed on the insulating film with a resist layer, and forming holes in the resist layer to expose part of the wiring pattern; plating the wiring pattern within the holes to form the protruded electrodes; removing the resist layer; forming the bump on each of the protruded electrodes in such a manner that the bump is bonded to the at least entire end face of each of the protruded electrodes; and effecting sealing, after forming the bump, by supplying a resin to the wiring pattern to form a protective film. 
     Since the protective film is formed after forming bumps, the bumps each can be formed at a desired position of the protruded electrode, and the bond strength of the bumps can be increased. 
     Also in this case, the process is appropriate when the process comprises the plating step of forming a barrier plated layer on the end face of each of the protruded electrodes, and when the bump is formed in the bump-forming step in such a manner that the bump is bonded to the entire barrier plated layer. 
     Furthermore, in a process for producing a semiconductor device according to the present invention wherein a wiring pattern to be connected to an electrode of a semiconductor chip is formed on an insulating film formed on the semiconductor chip surface on which the electrode is formed, protruded electrodes are formed on the wiring pattern, the wiring pattern is covered with a protective film, and a bump for external connection is formed on the end portion of each of the protruded electrodes exposed from the protective film, the process comprises the steps of: covering the wiring pattern formed on the insulating film with a resist layer, and forming holes in the resist layer to expose part of the wiring pattern; plating the wiring pattern within the holes to form the protruded electrodes; removing the resist layer; forming the bump on each of the protruded electrodes in such a manner that the bump is bonded to the at least entire end face of each of the protruded electrodes; forming a photosensitive resist layer to cover the wiring pattern and the protruded electrodes; and effecting photolithography by exposing to light and developing the photosensitive resist layer to form a protective film which covers the wiring pattern and to expose the protruded electrodes. 
     Since the protective film is formed after forming bumps also in this process, the bumps can be formed without being influenced by the protective film, and the bond strength of the bumps can be increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing the step of forming an insulating film on a wafer; 
     FIG. 2 is a sectional view showing the step of forming a bonded metal layer and a copper layer on an insulating film; 
     FIG. 3 is a sectional view showing the step of forming a wiring pattern; 
     FIG. 4 is a sectional view showing the step of forming a protruded electrode; 
     FIG. 5 is sectional view showing a wafer on which protruded electrodes are formed; 
     FIG. 6 is a sectional view showing the step of supplying a resin on a wafer in a first embodiment; 
     FIG. 7 is a sectional view showing the shape of a protruded electrode; 
     FIG. 8 is a sectional view showing bumps bonded to protruded electrodes, respectively; 
     FIG.  9 ( a ) and FIG.  9 ( b ) are sectional views each showing the form of a bonded bump; 
     FIG. 10 is a sectional view showing bumps bonded to protruded electrodes, respectively, in a second embodiment; 
     FIG. 11 is a sectional view showing the step of supplying a resin on a wafer; 
     FIG. 12 is a sectional view showing the step of forming a photosensitive resist layer in a third embodiment; 
     FIG. 13 is a sectional view showing the step of forming a protective film with a photosensitive resist layer; 
     FIG. 14 is a sectional view showing a gap formed between a protective film and a protruded electrode; 
     FIG. 15 is a sectional view showing a protrusion formed at the end of a protruded electrode; and 
     FIG. 16 is a sectional view showing a bump in the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Appropriate embodiments of the present invention will be explained below in detail based on the attached drawings. 
     Although a process for forming a rewiring pattern on a wafer is known, the process will be briefly explained by making reference to FIG. 1 to FIG.  4 . 
     Firstly, as shown in FIG. 1, an insulating film  23  composed of a polyimide resin is formed on a passivation film  21  of a wafer (semiconductor chip)  20  except for the portion for an aluminum electrode  22 . 
     Secondly, as shown in FIG. 2, a bonded metal layer  25  comprising double layers of titanium and chromium and a copper layer  26  are formed by sputtering. 
     Next, as shown in FIG. 3, a resist pattern  27  in which the copper layer  26  is exposed in a groove shape in the portion where a wiring pattern (rewiring pattern) is to be formed is formed. A plated film is formed on the copper layer  26  by electroplating of copper while the resist pattern  27  and the copper layer  26  are used as a mask and a conducting layer, respectively, thereby forming a wiring pattern  28 . 
     The resist pattern  27  is removed. 
     Next, as shown in FIG. 4, a resist layer  30  is formed on the wiring pattern  28 , and holes  31  are formed in the resist layer  30  to expose part of the wiring pattern  28 . 
     The wiring pattern  28  within the holes  31  is electroplated with copper to form protruded electrodes  32 . 
     A barrier plated layer  33  comprising a nickel coating and a gold coating is further formed on the end face of each of the protruded electrodes  32 . The barrier plated layer  33  may also comprise two layer coatings formed with a nickel coating and a palladium coating. 
     The resist layer  30  is then removed. 
     The exposed copper layer  26  and the bonded metal layer  25  are removed by etching, thereby isolating the wiring pattern  28 . 
     The wafer  20  on which the insulating film  23 , the wiring pattern  28  and the protruded electrodes  32  have been formed can thus be obtained (FIG.  5 ). 
     First Embodiment 
     Next, as shown in FIG. 6, a resin composed of an epoxy resin, etc. is supplied to the wiring pattern  28  from a nozzle  34 , flattened, and cured to form a protective film  36 . Spin coating is suitable for flattening the resin. 
     The level of the protective film  36  is made lower than that of the protruded electrodes  32 . 
     Specifically, when the protruded electrodes  32  are formed by electroplating to make a protrusion, the center of the end face of each of the electrodes becomes protuberant to some extent as shown in FIG.  7 . The protective film  36  is formed in such a manner that the level of the film becomes lower than that of the edge portion of the barrier plated layer  33 . 
     A solder bump  38  is subsequently formed on each of the protruded electrodes  32  as shown in FIG.  8 . 
     The solder bump  38  is formed in such a manner that the bump  38  is bonded to the entire barrier plated layer  33  having good wettability (FIG.  9 ( a )). That is, an oxide film is formed on the peripheral surface of the protruded electrode  32  formed with copper. Since the wettability of solder with the oxide film is poor, the solder bump  38  is formed so that the bump is bonded to the entire barrier plated layer  33 . In addition, when a highly active flux is used, the oxide film on the peripheral surface of the protruded electrode  32  is sometimes removed, and the solder bump  38  adheres to the portion where the oxide film has been removed. The state is included in the state where “the bump is bonded to the entire barrier plated layer  33 ” in the present invention (FIG.  9 ( b )). 
     As explained above, since the bump is formed while the bump is bonded to the entire end face of the protruded electrode  32 , in more detail, the bump is bonded to the entire barrier plated layer, a large bond area is obtained, and the bond strength of the bump  38  can be increased. Moreover, the bond angle made by the solder bump  38  with the protruded electrode does not become an acute angle; therefore, the solder bump is also excellent in strength on impact. 
     In addition, the entire end face of the protruded electrode  32  designates the entire end face included within the sectional area of the protruded electrode  32  (within the area of the plan view thereof) even when the end face forms a curved surface. 
     Second Embodiment 
     FIG.  10  and FIG. 11 show a second embodiment. 
     In the present embodiment, the solder bumps  38  are firstly formed on the protruded electrodes  32 , respectively, on the wafer  20  shown in FIG. 5, as shown in FIG.  10 . 
     Similarly to FIG. 9, also in this case, since an oxide film is formed on the peripheral surface of each of the protruded electrodes  32 , the protruded electrodes show poor wettability with solder; therefore, the solder bumps  38  are each determined to be bonded to the entire barrier plated layer  33 . 
     Next, as shown in FIG. 11, a resin such as an epoxy resin is supplied from a nozzle  34  to the wiring pattern  28 , and cured to form a protective film  36 . 
     The level of the protective film  36  is arbitrary in this case. That is, since each of the bumps  38  has already been bonded to the protruded electrode  32  to form a necessary bond area, the bond strength of the bumps  38  is not influenced by the protective film  38 . 
     Third Embodiment 
     In the present embodiment, the solder bumps  38  are formed on the protruded electrodes  32 , respectively, as shown in FIG. 10 for the second embodiment, and a photosensitive resist layer  40  is formed to cover the wiring pattern  28  and even the top of the solder bumps  38  as shown in FIG.  12 . 
     Next, as shown in FIG. 13, the photosensitive resist layer  40  is exposed and developed by photolithography to form a protective film  42  which covers the wiring pattern  28  and to disclose the protruded electrodes  32 . 
     A positive photosensitive resist is used for the photosensitive resist layer  40 . Control of the exposure time can control the depth of exposure, and as a result the thickness of the resist layer, which can be removed by etching, can be controlled. 
     Furthermore, since the light does not impinge on a portion near the root of each of the solder bumps  38 , the resist layer covering the periphery of the bond portion between each of the solder bumps  38  and the corresponding protruded electrode  32  can be left as shown in FIG. 13, whereby the bond portion can be protected. 
     The bond strength of the solder bumps  38  can be increased also in the present embodiment. 
     In each of the embodiments mentioned above, each of the semiconductor devices can of course be completed separately by finally cutting the wafer  20 . 
     In addition, semiconductor devices can each be completed separately by cutting the wafer first to give separate semiconductor chips, and then following the steps as mentioned above. 
     In the second embodiment, as shown in FIG. 14, a gap (structure without adhesion) can be formed between the protective film  36  and the peripheral surface of the protruded electrode  32 , depending on the type of resin used. 
     That is, as explained above, an oxide film is formed on the peripheral surface of the protruded electrode  32 , and some resins show poor wettability with the protruded electrode when the oxide film is formed. As a result, the protective film  36  does not adhere to the peripheral surface of the protruded electrode  32 . 
     An oxide film may also be positively formed on the peripheral surface of the protruded electrode  32 . 
     Consequently, the protruded electrode  32  becomes independent of the protective film  36 , and is not influenced thereby even when the coefficient of thermal expansion of the electrode differs from that of the film. Stress concentration in the bond portion between the protruded electrode  32  and the bump  38  is relaxed, and crack formation, and the like, in the bond portion can be suppressed. 
     Also in this case, it is appropriate to form the protective film  36  in such a manner that its level becomes higher than the position at which the bump  38  is bonded to the protruded electrode  32 , and that part of the peripheral surface of the bump is contacted with the protective film  36  (FIG.  14 ). 
     As a result, the gap between the protruded electrode  32  and the protective film  36  can be closed, and invasion of moisture, and the like, can be prevented. 
     FIG. 15 shows another embodiment of the end face shape of the protruded electrode  32 . 
     In the present embodiment, the end face central portion of the protruded electrode  32  has a still more protuberant shape (protruded portion  32  a). 
     In order to form such a protruded portion  32  a, the following procedure is recommended. A split  28  a is adhered to the wiring pattern  28  when the protruded electrode  32  is to be formed by plating, and the protruded electrode  32  is formed on the wiring pattern  28  including the slip  28  a by plating. Since the plated coating is formed to have an approximately uniform thickness, the protruded portion  32  a corresponding to the split  28  can be formed. 
     The split  28  a can be formed by plating during the step of forming the wiring pattern  28 . 
     Formation of such a protruded portion  32 a can increase the end face area of the protruded electrode  32 , which further increases the bond strength of the bump  38 . 
     The present invention has been explained above in various ways by making reference to appropriate embodiments. However, the present invention is not restricted to the embodiments, and many modifications of the present invention are naturally possible so long as the modifications do not depart from the spirit and the scope of the invention. 
     According to the semiconductor device and the production process of the present invention, a semiconductor device excellent in the bond strength of the bumps can be provided.