Patent Publication Number: US-2013249089-A1

Title: Method for manufacturing fine-pitch bumps and structure thereof

Description:
FIELD OF THE INVENTION 
     The present invention is generally related to a method for manufacturing fine-pitch bumps, which particularly relates to the method for manufacturing fine-pitch bumps that prevents copper ions from dissociation. 
     BACKGROUND OF THE INVENTION 
     In structure of fine-pitch bumps, a short phenomenon is easily occurred from a relatively short gap between two adjacent copper bumps owing to the copper ion dissociated by the copper bump. 
     SUMMARY 
     The primary object of the present invention is to provide a method for manufacturing fine-pitch bumps comprising the following steps of providing a silicon substrate having a surface, a plurality of bond pads disposed at the surface and a protective layer disposed at the surface, wherein the protective layer comprises a plurality of openings, and the bond pads are revealed by the openings; forming a titanium-containing metal layer on the silicon substrate, the titanium-containing metal layer comprises a plurality of first zones and a plurality of second zones located outside the first zones, the protective layer and the bond pads are covered with the titanium-containing metal layer; forming a photoresist layer on the titanium-containing metal layer; patterning the photoresist layer to form a plurality of opening slots corresponded to the first zones of the titanium-containing metal layer; forming a plurality of copper bumps at the opening slots, each of the copper bumps comprises a first top surface and a ring surface; heating the photoresist layer to ream the opening slots of the photoresist layer, and the heat process enables the photoresist layer to form a plurality of body portions and a plurality of removable portions; etching the photoresist layer to remove the removable portions and expose the titanium-containing metal layer; forming a plurality of bump protection layers on the titanium-containing metal layer, the first top surface and the ring surface of each of the copper bumps, wherein each of the bump protection layers comprises a metallic coverage portion and a bump coverage portion having a second top surface, the first top surface and the ring surface of each of the copper bumps are covered with the bump coverage portion; forming a plurality of wettable layers on the second top surfaces; removing the body portions of the photoresist layer; eventually, removing the second zones of the titanium-containing metal layer to enable each of the first zones of the titanium-containing metal layer to form an under bump metallurgy layer located under each of the copper bumps, each of the under bump metallurgy layers comprises a bearing portion located under each of the copper bumps and an extending portion protruded to the ring surface of each of the copper bumps, and the extending portion of each of the under bump metallurgy layers is covered with the metallic coverage portion of each of the bump protection layers. The protection of the bump protection layers may lower dissociation of copper ions released from the copper bumps, which improves reliability of the fine-pitch bump structure effectively. Besides, the protection also prevents the copper bumps from collapsing when removing the second zones of the titanium-containing metal layer. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow illustrating a method for manufacturing fine-pitch bumps in accordance with a preferred embodiment of the present invention. 
         FIGS. 2A to 2K  are sectional schematic diagrams illustrating a method for manufacturing fine-pitch bumps in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 and 2A  to  2 K, a method for manufacturing fine-pitch bumps in accordance with a preferred embodiment of the present invention comprises the following steps of: first, with reference to step  11  of  FIG. 1  and  FIG. 2A , providing a silicon substrate  110  having a surface  111 , a plurality of bond pads  112  disposed at the surface  111  and a protective layer  113  disposed at the surface  111 , wherein the protective layer  113  comprises a plurality of openings  113   a,  and the bond pads  112  are revealed by the openings  113   a;  next, referring to step  12  of  FIG. 1  and  FIG. 2B , forming a titanium-containing metal layer  200  on the silicon substrate  110 , the titanium-containing metal layer  200  comprises a plurality of first zones  210  and a plurality of second zones  220  located outside the first zones  210 , the protective layer  113  and the bond pads  112  are covered with the titanium-containing metal layer  200 ; thereafter, referring to step  13  of  FIG. 1  and  FIG. 2C , forming a photoresist layer  300  on the titanium-containing metal layer  200 ; afterwards, referring to step  14  of  FIG. 1  and  FIG. 2D , patterning the photoresist layer  300  to form a plurality of opening slots  310  corresponded to the first zones  210  of the titanium-containing metal layer  200 ; then, referring to step  15  of  FIG. 1  and  FIG. 2E , forming a plurality of copper bumps  120  at the opening slots  310 , each of the copper bumps  120  comprises a first top surface  121  and a ring surface  122 . 
     Next, referring to step  16  of  FIG. 1  and  FIG. 2F , heating the photoresist layer  300  to ream the opening slots  310  of the photoresist layer  300 , and the heat process enables the photoresist layer  300  to form a plurality of body portions  320  and a plurality of removable portions  330 , in this embodiment, the glass transition temperature in the heat process ranges from 70 to 140 degrees; afterwards, referring to step  17  of  FIG. 1  and  FIG. 2G , etching the photoresist layer  300  to remove the removable portions  330  and expose the titanium-containing metal layer  200 , in this embodiment, the method for etching the photoresist layer  300  can be a method of plasma dry etching; thereafter, with reference to step  18  of  FIG. 1  and  FIG. 2H , forming a plurality of bump protection layers  130  on the titanium-containing metal layer  200 , the first top surface  121  and the ring surface  122  of each of the copper bumps  120 , wherein each of the bump protection layers  130  comprises a metallic coverage portion  132  and a bump coverage portion  131  having a second top surface  131   a,  the first top surface  121  and the ring surface  122  of each of the copper bumps  120  are covered with the bump coverage portion  131 , in this embodiment, the material of the bump protection layers  130  can be chosen from one of nickel, palladium or gold. 
     Next, referring to step  19  of  FIG. 1  and  FIG. 2I , forming a plurality of wettable layers  140  on the second top surfaces  131   a  of the bump coverage portions  131 ; afterwards, referring to step  20  of  FIG. 1  and  FIG. 2J , removing the body portions  320  of the photoresist layer  300  to reveal the wettable layers  140  and the bump protection layers  130 ; eventually, referring to step  21  of  FIG. 1  and  FIG. 2K , removing the second zones  220  of the titanium-containing metal layer  200  to enable each of the first zones  210  of the titanium-containing metal layer  200  to form an under bump metallurgy layer  150  located under each of the copper bumps  120  therefore forming a fine-pitch bump structure  100 , wherein each of the under bump metallurgy layers  150  comprises a bearing portion  151  located under each of the copper bumps  120  and an extending portion  152  protruded to the ring surface  122  of each of the copper bumps  120 , the protective layer  113  is partly covered with the extending portion  152  of the under bump metallurgy layers  150 , and the extending portion  152  of each of the under bump metallurgy layers  150  is covered with the metallic coverage portion  132  of each of the bump protection layers  130 . The under bump metallurgy layers  150  are made of a material selected from one of titanium/tungsten/gold, titanium/copper and titanium/tungsten/copper. In addition, in this embodiment, each of the bump coverage portions  131  comprises a first outer lateral surface  131   b,  wherein each of the metallic coverage portions  132  is protruded to the first outer lateral surface  131   b  of the bump coverage portion  131  and comprises a second outer lateral surface  132   a.  Furthermore, the extending portion  152  of each of the under bump metallurgy layers  150  comprises a third outer lateral surface  152   a  coplanar with the second outer lateral surface  132   a.  The copper bumps  120  being covered by the bump protection layers  130  may lower dissociation of copper ions released from the copper bumps  120 , which improves reliability of the fine-pitch bump structure  100  effectively. Besides, the protection of the bump protection layers  130  may prevent the copper bumps  120  from collapsing when removing the second zones  220  of the titanium-containing metal layer  200 . 
     With reference to  FIG. 2K  again, a fine-pitch bump structure  100  in accordance with a preferred embodiment of the present invention at least comprises a silicon substrate  110 , a plurality of under bump metallurgy layers  150 , a plurality of copper bumps  120 , a plurality of bump protection layers  130 , and a plurality of wettable layers  140 , wherein the silicon substrate  110  comprises a surface  111 , a plurality of bond pads  112  disposed at the surface  111  and a protective layer  113  disposed at the surface  111 . The protective layer  113  comprises a plurality of openings  113   a,  and the bond pads  112  are revealed by the openings  113   a.  The under bump metallurgy layers  150  are formed on the bond pads  112 , each of the under bump metallurgy layers  150  comprises a bearing portion  151  and an extending portion  152 , and the under bump metallurgy layers  150  are made of a material selected from one of titanium/tungsten/gold, titanium/copper and titanium/tungsten/copper. The copper bumps  120  are formed on the under bump metallurgy layers  150 , and each of the copper bumps  120  comprises a first top surface  121  and a ring surface  122 . The bearing portion  151  of each of the under bump metallurgy layers  150  is located under each of the copper bumps  120 , and the extending portion  152  of each of the under bump metallurgy layers  150  is protruded to the ring surface  122  of each of the copper bumps  120 . The bump protection layers  130  are formed on the extending portions  152  of the under bump metallurgy layers  150 , the first top surface  121  and the ring surface  122  of each of the copper bumps  120 . Each of the bump protection layers  130  comprises a metallic coverage portion  132  and a bump coverage portion  131  having a second top surface  131   a,  wherein the first top surface  121  and the ring surface  122  of each of the copper bumps  120  are covered with each of the bump coverage portions  131 , and the extending portion  152  of each of the under bump metallurgy layers  150  is covered with each of the metallic coverage portions  132 . In this embodiment, the material of the bump protection layers  130  can be chosen from one of nickel, palladium or gold. The wettable layers  140  are formed on the second top surfaces  131   a  of the bump coverage portions  131 . The bump coverage portion  131  further comprises a first outer lateral surface  131   b,  the metallic coverage portion  132  is protruded to the first outer lateral surface  131   b  and comprises a second outer lateral surface  132   a,  and the extending portion  152  of each of the under bump metallurgy layers  150  comprises a third outer lateral surface  152   a  coplanar with the second outer lateral surface  132   a.    
     While this invention has been particularly illustrated and described in detail with respect to the preferred embodiments thereof, it will be clearly understood by those skilled in the art that it is not limited to the specific features and describes and various modifications and changes in form and details may be made without departing from the spirit and scope of this invention.