Patent Publication Number: US-2006003587-A1

Title: Grinding method for a sapphire wafer

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a grinding method for a sapphire wafer, particularly to a grinding method for a sapphire wafer, which is applied to light emitting diodes.  
      2. Description of the Related Art  
      LED (light emitting diode) is a luminescent light-emitting element and can convert electric energy into light energy in high efficiency. LED is also a tiny solid-state light source. LED primarily comprises a p-n junction of semiconductor, and when an appropriate voltage is applied to both ends of the p-n junction, the combination of electrons and electron holes will emit photons. LED has the advantages of miniature size, low power consumption, little heat generation, long service life, and superior vibration resistance. LED has been extensively used in daily living, such as illumination devices, backlight sources, advertisement signs, traffic signals, electric torches, camera flashlights, and decoration lights.  
      In the application of large-size LED, such as a big signboard, LED also needs to have high brightness. However, high brightness is equal to high energy, and the temperature of LED will rise to high. If the heat resistance LED is insufficient, large-size LED may incur a danger.  
      Therefore, a technology utilizing a sapphire wafer to fabricate LED has been developed. As a sapphire wafer has the advantages of high hardness, high transparency, high melting point, and high heat resistance, the LED fabricated with a sapphire wafer can work normally at high temperature. When a sapphire wafer is used to fabricate LED, the sapphire will have an insulation layer. Currently, the insulation layer is removed via a laser method. However, the laser method makes the cost rise. Besides, the removing speed is very low, which increases the fabrication time of LED.  
      Accordingly, the present invention proposes a grinding method for a sapphire wafer to overcome the abovementioned problems.  
     SUMMARY OF THE INVENTION  
      The primary objective of the present invention is to provide a grinding method for a sapphire wafer, wherein the substrate of a sapphire wafer is completely removed not via a laser method but via an etching method, and the fabrication cost thereof is lowered.  
      Another objective of the present invention is to provide a grinding method for a sapphire wafer, wherein the substrate of a sapphire wafer is removed via a machining table, polishing liquid, and an etching method, and the time for removing the substrate is shortened, and LED fabrication is also accelerated.  
      Yet another objective of the present invention is to provide a grinding method for a sapphire wafer, wherein a heat-resistant sapphire wafer is used in LED fabrication, which reduces the danger incurred by LED&#39;s working at high temperature and enables LED to work normally at high temperature.  
      To achieve the aforementioned objectives, the present invention proposes a grinding method for a sapphire wafer, wherein a sapphire wafer is firstly provided, and the sapphire wafer has a substrate and an electrically-conductive layer; the sapphire wafer is fixed to a fixing base; the fixing base is further fixed to a machining table, and the substrate of the sapphire wafer is ground thereon; then, the substrate is further thinned; lastly, the substrate is completely removed via an etching method, and the electrically-conductive layer is exposed.  
      To enable the objectives, technical contents, characteristics, and accomplishments of the present invention to be more easily understood, the embodiments of the present invention are to be described below in detail in cooperation with the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1 ( a ) to  FIG. 1 ( d ) show schematically the steps of the grinding method for a sapphire wafer according to the present invention.  
       FIG. 2  is a section view showing that a metallic layer is joined to the bottom of the sapphire wafer according to the method of the present invention.  
       FIG. 3  is a section view of LED fabricated according to the method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Refer to from  FIG. 1 ( a ) to  FIG. 1 ( d ) showing the steps of the grinding method for a sapphire wafer according to the present invention. In the present invention, three sapphire wafers  22  are firstly provided. As shown in  FIG. 1 ( a ), each sapphire wafer  22  comprises a substrate  222  and an electrically-conductive layer  224 , wherein the substrate  222  is an insulation layer. Next, as shown in  FIG. 1 ( b ), those three sapphire wafers  22  are stuck to a fixing base  24  with a wax, and a pressure ranging from 1 to 10 kg/cm 2  is applied to fix those sapphire wafers  22  onto the fixing base  24 , wherein the fixing base  24  may be made of a ceramic material. Next, as shown in  FIG. 1 ( c ), the fixing base  24  is further fixed onto a machining table  26  via a vacuum-suction method, and the substrate  222  of the sapphire wafers  22  are roughly ground to a thickness of from 50 to 200 μm. Next, as shown in  FIG. 1 ( d ), a fine grinding follows, and the fixing base  24  is disposed on a polishing disc  28 , and a polishing solution is used to thin the substrate  222  of the sapphire wafers  22  to a thickness less than 10 μm. Lastly, the substrate  222  is completely removed via an etching method, wherein the etching method may be either a dry etching or a wet etching, and the electrically-conductive layer  224  is thus exposed.  
      Refer to  FIG. 1 ( c ). The machining table  26  has a first transmission device  262  and a second transmission device  264 , wherein the first and the second transmission devices  262 ,  264  may both be motors. The second transmission device  264  has a grinding wheel  266 , and the grinding wheel  266  may comprises diamonds. The fixing base  24  is fixed onto the first transmission device  262  via a vacuum-suction method, and the grinding wheel  266  is disposed corresponding to the sapphire wafers  22  on the fixing base  24 . The first transmission device  262  can drive the fixing base  24  to move back and forth for some distance according to grinding parameters stored in a control device  27 , and the grinding parameters includes thickness ground off, grinding time, and a grinding mode. The control device  27  controls the second transmission device  264  to rotate and move left or right. Thereby, the sapphire wafers  22  and the grinding wheel  266  can move to each other, and the substrates  222  of the sapphire wafers  22  can be roughly ground. Further, two coolant nozzles  268  are installed in the machining table  26  to spray a liquid coolant in order to cool the sapphire wafers  22  and the grinding wheel  266  lest the temperature rise too much in the rough grinding.  
      The sapphire wafer of the present invention can be applied to a large-size LED. When the sapphire wafer is applied to LED, a metallic layer  226  or another wafer is firstly joined onto the bottom of the electrically-conductive layer  224  of the sapphire wafer  22 , and the metallic layer is made of a metal, which can replace the substrate  222  of the sapphire wafer  22 , such as copper, gold, molybdenum, or aluminum. The substrate  222  of the sapphire wafer  22  is an insulator, which is to be replaced by the metallic layer  226  or another wafer. The electrically-conductive layer  224  and the metallic layer  226 /another wafer have electrodes of opposite polarities. Next, as shown in  FIG. 1 ( b ), the sapphire wafer  22  is fixed to the fixing base  24 , and the following is the same as the grinding steps mentioned above, and it is no more described repeatedly herein. As shown in  FIG. 3 , after the substrate  222 —the insulation layer—of the sapphire wafer  22  has been completely removed, only the electrically-conductive layer  224  and the metallic layer  226 /another wafer remain. When the electrically-conductive layer  224  and the metallic layer  226 /another wafer having opposite-polarity electrodes are enabled to be conductive to form a conductor  30 , it becomes an LED and can illuminate.  
      The present invention proposes a grinding method for a sapphire wafer, which can be used to fabricate large-size LED&#39;s, and wherein the substrate of a sapphire wafer is completely removed not via a laser method but via an etching method, and the fabrication cost thereof is lowered, and wherein the substrate of a sapphire wafer is removed via a machining table, polishing liquid, and an etching method, and the time for removing the substrate is shortened, and LED fabrication is also accelerated, and wherein a heat-resistant sapphire wafer is used for fabricating LED, which reduces the danger incurred by LED&#39;s working at high temperature and enables LED to work normally at high temperature.  
      Those embodiments described above are to clarify the present invention to enable the persons skilled in the art to understand, make, and use the present invention but not intended to limit the scope of the present invention. Any equivalent modification and variation according to the spirit of the present invention is to be included within the scope of the present invention.