Abstract:
A bonding pad structure. A substrate having a first surface and a second surface is provided. A metal bonding pad and a bonding region are respectively located on the first surface and the second surface. Intermediate plated layers located are on the metal bonding pad and the bonding region. Under ball metallurgy layers are located on each of the intermediate plated layers such that each of the under ball metallurgy layers comprises a first plated layer and a second plated layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of, and claims the priority benefit of, U.S. application Ser. No. 09/335,635 filed on Jun. 18, 1999, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a bonding pad structure and a method for fabricating the same. More particularly, the present invention relates to a bonding pad structure of a power device and a method for fabricating the same. 
     2. Description of Related Art 
     As chip integration increases, various semiconductor packages are used, such as chip scale package or multi-chip module. However, a leadframe is usually used for packaging a low pin count chip such as a power device. 
     FIG. 1 is a schematic, three-dimensional diagram of a conventional power device. 
     Referring to FIG. 1, a conventional power device is formed on a substrate  100 . 
     The power device includes a source region  102 , a gate  104 , an insulating layer  106  surrounding the gate  104  and a drain region  108  opposite the source region  102  and the gate  104 . A material of the insulating layer  106  is phosphosilicate glass (PSG). The source region  102  is a stack made of a titanium layer (not shown), a titanium nitride layer (not shown) and an aluminum-silicon-copper alloy layer (not shown); the drain region  108  comprises the same material as the substrate  100 . 
     FIG. 2 is a schematic, cross-sectional diagram of a conventional bonding pad structure of a power device. 
     Referring to FIG. 2, an aluminum bonding pad layer  204  is formed on a surface  202   a  of a substrate  200 . A surface  202   b  of the substrate  200  is grounded to reduce the thickness of the substrate  200  after the semiconductor manufacturing processes are completed. An under ball metallurgy (UBM) layer  214   a  is formed on a portion of the aluminum bonding pad layer  204  located in a bonding pad window  206 . The under ball metallurgy layer  214   a  is made of a titanium layer  208   a , a nickel layer  210   a  and a silver layer  212   a ; the layers are formed by sputtering. 
     An under ball metallurgy layer  214   b  is then formed on a portion of a surface  202   b  located in a bonding region  216 , and it is made from a titanium layer  208   b , a nickel layer  210   b  and a silver layer  212   b . The layers are formed by sputtering. 
     In the power device mentioned above, the under ball metallurgy layer  214   a ,  214   b  are individually formed in their own formation processes; thus, the manufacturing processes become complex. It is difficult to reduce the manufacturing costs. 
     Electroless plating is another method to form the under ball metallurgy layers. Since the layers on the aluminum bonding pad layer are different from those on the bonding region, various conditions are possible for the electroless plating process. For example, the substrate should be dipped into an alkaline solution to form a nickel layer on the bonding region. The substrate is dipped into an acidic solution to form a nickel layer on the aluminum bonding pad layer. Again, the under ball metallurgy layers are still individually formed, so electroless plating also increases the manufacturing time and the manufacturing costs. 
     SUMMARY OF THE INVENTION 
     The invention provides a bonding pad structure and a method for fabricating the same. In the invention, under ball metallurgy layers over a bonding pad and a bonding region are simultaneously formed by electroless plating so that manufacturing processes are simplified and manufacturing costs are reduced. Furthermore, the under ball metallurgy layers can provide good bondability and solderability. Intermediate plated layers are located between the bonding region and the under ball metallurgy layer, as well as between the bonding pad and the under ball metallurgy layer, to improve adhesion between the under ball metallurgy layer and the metal bonding pad, and the under ball metallurgy layer and the bonding region. 
     The invention provides a bonding pad structure. A substrate having a first surface and a second surface is provided. A metal bonding pad and a bonding region are respectively located on the first surface and the second surface. Intermediate plated layers are located on the metal bonding pad and the bonding region. Under ball metallurgy layers are on each of the intermediate plated layers such that each of the under ball metallurgy layers comprises a first plated layer and a second plated layer. 
     The invention provides a method for fabricating a bonding pad structure. A substrate having a first surface and a second surface is provided. A metal bonding pad is formed on the first surface, and a bonding region is defined on the second region. Intermediate plated layers are simultaneously formed on the metal bonding pad and the bonding region by electroless plating. Then, under ball metallurgy layers are simultaneously formed on each of the intermediate plated layers by electroless plating in which each of the under ball metallurgy layers comprises a first plated layers and a second plated layer. 
     In the invention, the intermediate plated layers are formed simultaneously by electroless plating, and the under ball metallurgy layers are the same. By this invention, the manufacturing processes are simplified, and the manufacturing costs and the manufacturing time are both reduced. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1 is a schematic, three-dimensional diagram of a conventional power device; 
     FIG. 2 is a schematic, cross-sectional diagram of a conventional bonding pad structure of a power device; and 
     FIGS. 3A through 3D are schematic, cross-sectional diagrams of a method for fabricating a bonding pad structure according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 3A through 3D are schematic, cross-sectional diagrams of a method for fabricating a bonding pad structure according to the invention. 
     Referring to FIG. 3A, a substrate  300  having surfaces  302   a ,  302   b  is provided. The substrate  300  includes devices (not shown) such as power devices. A metal bonding pad  304  is formed on the surface  302   a , and a bonding region  306  is defined on the surface  302   b . The metal bonding pad  304  includes aluminum or other kinds of conductive metal. 
     The substrate  300  is cleaned by performing a cleaning process. For example, the cleaning process includes the following steps. The substrate  300  is degreased by acetone for about 10 minutes. The substrate  300  is rinsed with deionized water for about 2 minutes. The substrate  300  is then etched by a mixture comprising hydrofluoric acid (HF) and nitric acid (HNO 3 ) for about 2 minutes. In the mixture, the concentration of hydrofluoric acid is preferably about 5 ml/L, and that of nitric acid is about 200 ml/L. The substrate  300  is rinsed with deionized water for about 2 minutes. 
     Referring to FIG. 3B, an electroless plating process is performed; intermediate plated layers  308   a  are simultaneously formed on the metal bonding pad  304  and the bonding region  306 . The thickness of the intermediate plated layer  308   a  on the metal bonding pad  304  is approximately equal to that of the intermediate plated layer  308   a  on the bonding region  306 . The intermediate plated layers  308   a  include zinc, and the intermediate plated layers  308   a  are preferably formed by the following steps. The substrate  300  is dipped in a zincate solution for about 2 minutes to form the intermediate plated layers  308   a . Then, the substrate  300  is rinsed with deionized water for about 5 minutes. The substrate  300  is dipped in a solution including nitric acid and water to roughen surfaces of the intermediate plated layers  308   a . The substrate  300  is then rinsed with deionized water. By roughening surfaces of the intermediate plated layers  308   a , adhesion between the intermediate plated layers  308   a  and subsequently formed intermediate plated layers can be improved and the thicknesses of the subsequently formed intermediate plated layers can also be uniform. 
     Intermediate plated layers  308   b  are then simultaneously formed on each of the intermediate plated layers  308   a . The material and the method of forming the intermediate plated layers  308   b  are similar to those of the intermediate plated layers  308   a , so detailed descriptions are omitted here. Additionally, the thickness of the intermediate plated layer  308   a  is approximately equal to that of the intermediate plated layer  308   b . Each of the intermediate plated layers  308   a  and each of the intermediate plated layers  308   b  constitute an intermediate layer  308 . 
     Referring to FIG. 3C, an electroless plating process is performed after the intermediate plated layers  308  are formed on the metal bonding pad  304  and the bonding region  306 ; then, plated layers  310  are simultaneously formed on each of the intermediate plated layer  308 . The plated layer  310  includes nickel. The method of forming the plated layer  310  preferably includes the following steps. The substrate  300  is dipped in a nickel kit solution whose pH value is about 8.8-9.0 at about 90° C. for about 10 minutes, and then the substrate  300  is rinsed with deionized water for about 2 minutes. Since the plated layers  310  are both formed on the intermediate plated layers  308  such that each of the intermediate plated layers  308  has the same material and the same thickness, the thicknesses of the plated layers  310  are both uniform. 
     Referring to FIG. 3D, an electroless plating process is performed after the plated layers  310  are formed; plated layers  312  which are, for example, gold are formed on each of the plated layer  310 . Each of the plated layers  310  and each of the plated layers  312  constitute an under ball metallurgy layer  314 . The method of forming the plated layer  312  includes the following steps. The substrate  300  is dipped in an aurosine solution whose pH value is about 7 at about 90° C. for about 1.5 minutes, and then the substrate  300  is rinsed with deionized water for about 2 minutes. Then, the substrate  300  is dipped into an acetone solution for cleaning. Because the plated layers  312  are both formed on the plated layers  310  that each of the plated layers  310  also has 
     the same material and the same thickness, the thicknesses of the plated layers  312  are both uniform. 
     In the invention, the intermediate plated layers are formed simultaneously on the metal bonding pad and the bonding region by electroless plating; thus, the manufacturing processes are simplified. Additionally, the intermediate plated layers improve adhesion between the under ball metallurgy layer and the metal bonding pad, and the under ball metallurgy layer and the bonding region. 
     Since the thicknesses of the under ball metallurgy layers are uniform, the electronic character of the under ball metallurgy layers can be maintained. Furthermore, the under ball metallurgy layers can provide good bondability and solderability; thus, the reliability and the yield are increased. 
     In the invention, the intermediate plated layers are formed simultaneously by electroless plating, and the under ball metallurgy layers are the same. As a result, the manufacturing processes are simplified, and the manufacturing costs and the manufacturing time are both reduced. 
     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.