Patent Publication Number: US-2007116864-A1

Title: Metal layer formation method for diode chips/wafers

Description:
This application claims the priority benefit of Taiwan patent application number 094140951 filed on Nov. 22, 2005.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method of forming a metal layer in a diode structure and more particularly, to an electroless plated metal layer formation method for diode chips/wafers.  
      2. Description of the Related Art  
      In light emitting diodes and laser diodes, light is a form of energy that can be released by an atom. It is made up of many photons that are the most basic units of light. Photons are released as a result of moving electrons. In an atom, electrons move in orbitals around the nucleus. Light emitting diodes and laser diodes are found in all kinds of devices in our daily life for the advantages of small size, long life, low driving voltage, low power consumption, and fast reactive speed.  
      According to conventional manufacturing technology, vapor deposition and sputtering deposition are commonly employed to the fabrication of light emitting diodes and laser diodes. These deposition methods cause deposition of the applied metal target material on the workpiece as well as the inside surface of the peripheral wall of the vacuum chamber, i.e., these deposition methods result in waste of the metal target material and contamination of the vacuum chamber, thereby affecting the quality of the deposited metal layer. In case the so-called double-sided treatment is necessary, the vacuum status of the vacuum chamber must be destroyed and then the wafer must be turned upside down for further deposition, prolonging the manufacturing time.  
      Therefore, it is desirable to provide an electroless plated metal layer formation method for diode chips/wafers that eliminates the aforesaid drawbacks.  
     SUMMARY OF THE INVENTION  
      The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide an electroless plated metal layer formation method, which is practical to form a uniform metal layer on each of two opposite sides of a diode chip or wafer, thereby shortening the manufacturing process and significantly lowering the manufacturing cost.  
      It is another object of the present invention to provide an electroless plated metal layer formation method, which employs an electroless plating process to selectively form a metal layer on or around the metal base material instead of whole surface vapor or sputtering deposition, thereby saving consumption of metal material and electric power and lowering operating and manufacturing cost.  
      It is still another object of the present invention to provide an electroless plated metal layer formation method, which requires an expense on equipment much lower than vapor deposition or sputtering deposition, thereby saving equipment investment and lower the manufacturing cost.  
      It is still another object of the present invention to provide an electroless plated metal layer formation method, which is practical to form a metal layer that has a rough surface suitable for wiring bonding or soldering, thereby improving the reliability of the product quality and enhancing the market competivity of the product.  
      It is still another object of the present invention to provide an electroless plated metal layer formation method, which is practical to form a metal layer suitable for forming metal bumps, metal pads, metal wires or heat plate, or for the purposes of wire bonding, soldering, or flip-chip package.  
      To achieve these and other objects of the present invention, the electroless plated metal layer formation method includes the steps of: (a): providing a diode chip/wafer; (b): forming on the diode chip/wafer at least one predetermined location a patterned metal base material; and (c): employing an electroless metal reduction wet process to form a metal layer on the diode chip/wafer that surrounds the border of the patterned metal base material on the diode chip/wafer at each of the at least one predetermined location.  
      According to an alternate form of the present invention, the electroless metal layer formation method includes the steps of: (a): providing a diode chip/wafer; (b): forming on the diode chip/wafer at predetermined locations a patterned metal base material; (c): forming on the diode chip/wafer an isolation layer over the patterned metal base material; (d): forming openings on the isolation layer subject to a predetermined pattern to have the patterned metal base material be exposed to the outside; and (e): employing an electroless plating process to deposit a metal layer on the patterned metal base material corresponding to the openings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic drawing of a finished product obtained according to one embodiment of the present invention.  
       FIG. 2  is a flow chart showing the fabrication of the finished product shown in  FIG. 1 .  
       FIG. 3  is a schematic drawing of a finished product obtained according to another embodiment of the present invention.  
       FIG. 4  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 5  is a flow chart showing the fabrication of the finished product shown in  FIG. 4 .  
       FIG. 6  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 7  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 8  is a flow chart showing the fabrication of the finished product shown in  FIG. 7 .  
       FIG. 9  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 10  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 11  is a flow chart showing the fabrication of the finished product shown in  FIG. 10 .  
       FIG. 12  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 13  is a flow chart showing the fabrication of the finished product shown in  FIG. 12 .  
       FIG. 14  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 15  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention.  
       FIG. 16  is a schematic drawing of a finished product according to still another embodiment of the present invention.  
       FIG. 17  is a schematic drawing of a finished product obtained according to still another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The invention relates to an electroless plated metal layer formation method for diode chips/wafers. The metal layer indicated herein can be metal bumps, metal pads, or a heat plate for wire bonding, solder bonding, conducting, flip-chip package, and many other purposes. Any products using the electroless plated metal layer formation method for diode chips/wafers should be included in the scope of the present invention.  
      First of all, the invention uses an electroless plating process to match with a metal base material for inducing a reduction system to cause a catalytic reaction, thereby forming a uniform metal layer having the desired thickness. A metal layer made according to the present invention can be thicker than 0.1 um. The material for the metal layer can be gold, nickel, copper, platinum, palladium, zinc, tin, silver or chrome, or their bimetal. The material for the metal base layer can also be gold, nickel, copper, platinum, palladium, zinc, tin, silver or chrome, or their bimetal. The metal base material can be formed by means of vapor deposition, electroplating, sputtering deposition, or electroless plating. In case gold is used for the metal layer, the electroless plating process is employed with a reacting solution containing a metal salt obtained from gold cyanide, sulfite gold, or gold trichloride.  
      The metal layer formed by means of the application of an electroless plating process according to the present invention may surround the metal base material. When wishing to limit the metal layer to specific locations on the metal base layer, an isolation layer is formed by means of the application of an dielectric material such as S i O 2 , photoresist, or PI, and then openings are formed on the isolation layer subject to the desired locations, and then an electroless plating process is employed to deposit the desired metal layer on the metal base layer in the openings of the isolation layer. After formation of the metal layer, the isolation layer is removed.  
      Referring to  FIGS. 1 and 2 , an electroless plated metal layer formation method for diode chips/wafers in accordance with a first embodiment of the present invention includes the steps of:  
      S1: providing a diode chip  10 ;  
      S2: forming on one each of two opposite sides of the diode chip  10  a metal base material adapted for inducing a reduction system to cause a catalytic reaction;  
      S3: employing lithography and etching to pattern the metal base material on each of the two opposite sides of the diode chip, so as to obtain a patterned metal base material  12 ; and  
      S4: employing an electroless plating process to form a metal layer  14  that surrounds the border of the patterned metal base material  12  on each of the two opposite sides of the diode chip.  
       FIG. 3  is a schematic drawing of a finished product obtained according to a second embodiment of the present invention. This second embodiment is substantially similar to the aforesaid first embodiment with the exception that this second embodiment has only patterned the metal base material  12  on one side of the diode chip.  
       FIG. 4  is a schematic drawing of a finished product obtained according to a third embodiment of the present invention.  FIG. 5  is a flow chart of the third embodiment shown in  FIG. 4 . According to this third embodiment, the electroless plated metal layer formation method includes the steps of:  
      S5: providing a diode chip  10 ;  
      S6: forming on one each of two opposite sides of the diode chip  10  a patterned metal base material  12  adapted for inducing a reduction system to cause a catalytic reaction;  
      S7: depositing on the patterned metal base material  12  on each of the two opposite sides of the diode chip  10  an isolation layer  16  by means of the application of an dielectric material such as S i O 2 , photoresist, or PI, and then making an opening  18  on the isolation layer  16  on the patterned metal base material  12  on each of the two opposite sides of the diode chip  10  to have a predetermined area of the patterned metal base material  12  be exposed to the outside; and  
      S8: employing an electroless plating process to form a metal layer  14  on the exposed predetermined area of the patterned metal base material  12  in the associating opening  18  on each of the two opposite sides of the diode chip.  
       FIG. 6  is a schematic drawing of a finished product obtained according to a fourth embodiment of the present invention. This fourth embodiment is substantially similar to the aforesaid third embodiment with the exception that this fifth embodiment only deposits an isolation layer  16  on the patterned metal base material  12  on one side of the diode chip  10 .  
       FIG. 7  is a schematic drawing of a finished product obtained according to a fifth embodiment of the present invention.  FIG. 8  is a flow chart of the fifth embodiment of the present invention. This fifth embodiment includes the steps of:  
      S5: providing a diode chip  10 ;  
      S6: forming on one each of two opposite sides of the diode chip  10  a patterned metal base material  12  adapted for inducing a reduction system to cause a catalytic reaction;  
      S7: depositing on the patterned metal base material  12  on each of the two opposite sides of the diode chip  10  an isolation layer  16  by means of the application of an dielectric material such as S i O 2 , photoresist, or PI, and then making an opening  18  on the isolation layer  16  on the patterned metal base material  12  on each of the two opposite sides of the diode chip  10  to have a predetermined area of the patterned metal base material  12  be exposed to the outside;  
      S8: employing an electroless plating process to form a metal layer  14  on the exposed predetermined area of the patterned metal base material  12  in the associating opening  18  on each of the two opposite sides of the diode chip; and  
      S9: removing the isolation layer  16  from each of the two opposite sides of the diode chip.  
       FIG. 9  is a schematic drawing of a finished product obtained according to a sixth embodiment of the present invention, which is a structure obtained after removal of the isolation layer  16  from the aforesaid fourth embodiment shown in  FIG. 6 .  
       FIG. 10  is a schematic drawing of a finished product obtained according to a finished product obtained according to a seventh embodiment of the present invention.  FIG. 11  is a flow chart of the seventh embodiment shown in  FIG. 10 . According to this seventh embodiment, the electroless plated metal layer formation method includes the steps of:  
      S10: preparing a diode chip  10  having electrodes arranged on the same side at different elevations;  
      S11: forming a patterned metal base material  12  on the diode chip  10  at predetermined locations;  
      S12: employing an electroless plating process to form a metal layer  14  that surrounds the border of the patterned metal base material  12  at each of the predetermined locations on the diode chip  10 .  
       FIG. 12  is a schematic drawing of a finished product obtained according to an eighth embodiment of the present invention. This embodiment employs to a diode chip having electrodes arranged on the same side at different elevations the concept of using an isolation layer to limit the deposition location of the metal layer on the metal base material as see in the aforesaid third embodiment of the present invention.  FIG. 11  is a flow chart of the seventh embodiment shown in  FIG. 10 . According to this eighth embodiment, the electroless plated metal layer formation method includes the steps of:  
      S13: preparing a diode chip  10  having electrodes arranged on the same side at different elevations;  
      S14: forming a patterned metal base material  12  on the diode chip  10  at predetermined locations;  
      S15: depositing on the patterned metal base material  12  on the diode chip  10  an isolation layer  16  by means of the application of an dielectric material such as S i O 2 , photoresist, or PI, and then making an opening  18  on the isolation layer  16  to have a predetermined area of the patterned metal base material  12  be exposed to the outside; and  
      S16: employing an electroless plating process to form a metal layer  14  on the exposed predetermined area of the patterned metal base material  12  corresponding to the opening  18 .  
       FIG. 14  is a schematic drawing of a finished product obtained according to a ninth embodiment of the present invention. This embodiment is obtained from the structure of the aforesaid eighth embodiment by removing the isolation layer  16  after formation of the metal layer  14 . Thereafter, metal wires  22  may be bonded to the metal layer  14  as shown in  FIG. 15 . Alternatively, a bonding layer  24  may be formed on the metal layer  14  for the bonding of a carrier plate  26  as shown in  FIG. 16 .  
       FIG. 17  is a schematic drawing of a finished product obtained according to a tenth embodiment of the present invention. This embodiment has a diode chip that has a metal layer formed by means of the application of an electroless plating process according to the present invention be mounted with a chip or carrier plate and bonded with metal wires. The exemplar shown in  FIG. 17  is based on the sixth embodiment of the present invention. As illustrated, one metal layer  14  at one side of the finished product of the aforesaid sixth embodiment of the present invention is bonded to a chip or carrier plate  26  with a bonding layer  24 , and a metal wire  22  is bonded to the other metal layer  14 .  
      As indicated above, the invention provides an electroless plated metal layer formation method for diode chips/wafers. The invention sues an electroless plating process to match with a metal base material for inducing a reduction system (reacting solution added with a metal substance) to cause a catalytic reaction, thereby forming a uniform metal layer having the desired thickness. This method is practical to deposit a metal layer on one or both sides of the diode chip/wafer, eliminating the step of turning the diode/chip/wafer to the other side as used in the prior art methods. The manufacturing process of the present invention is practical to form a metal layer of high uniformity. The operation of the present invention is easy, therefore the invention greatly shortens the manufacturing time, and lowers the manufacturing cost. A metal layer made according to the present invention has a surface rougher than a metal layer made by vapor deposition or sputtering deposition, and is practical for wire bonding or soldering, thereby improving the reliability of the product quality and enhancing the market competivity of the product.  
      A prototype of electroless plated metal layer formation method for diode chips/wafers has been constructed with the features of FIGS.  1 ˜ 17 . The electroless plated metal layer formation method for diode chips/wafers functions smoothly to provide all of the features disclosed earlier.  
      Although particular embodiment of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.