Method for backside die thinning and polishing of packaged integrated circuits

Abstract

A reliable, inexpensive “back side” thinning process, capable of globally as well as locally thinning an integrated circuit die to a target thickness of 10 microns, and maintaining a yield of at least 80%, for chip repair and/or failure analysis of the packaged die. The flip-chip or wire-bond packaged die is mounted on a thinning/polishing tool with the backside accessible. The thinning/polishing tool can be a lapping machine used for global thinning, or a mini milling machine, laser, FIB, or E-beam machine for local thinning. The thickness of the die is measured at at least five locations on the die before thinning. The thinning tool removes silicon on the exposed surface of the die to a thickness somewhat greater than the target thickness. The exposed surface of the die is polished. The thickness of the die is again measured optically with high accuracy. Based on the thickness data collected, appropriate machine operating parameters for further grinding and polishing of the exposed surface are determined. Further grinding and polishing are performed. These steps are repeated until the target thickness is reached.

We claim:  
     
         1 . A method of backside thinning of at least a portion of a packaged integrated circuit die to a predetermined thickness, comprising the steps of: 
 mounting the packaged die on a support;    measuring the thickness of the mounted packaged die at at least one location on the die;    contacting a region of the surface of the packaged die to a thinning medium to thin at least a portion of the die to a thickness greater than the predetermined thickness;    measuring the thickness of the thinned portion of the packaged die at at least one location;    based on the measurement of the thinned portion of the packaged die, determining parameters for further thinning;    performing further thinning according to the determined parameters; and    repeating the acts of determining the parameters and performing further thinning until the predetermined thickness is reached.    
     
     
         2 . The method of  claim 1 , wherein said step of contacting a region of the surface of the packaged die to a thinning medium to thin at least a portion of the die to a thickness greater than the predetermined thickness comprises grinding said surface of said packaged die.  
     
     
         3 . The method of  claim 2 , wherein said packaged die is flip-chip mounted.  
     
     
         4 . The method of  claim 3 , wherein: 
 said steps of measuring the thickness of the packaged die and of measuring the thickness of the thinned portion of the packaged die are performed at a plurality of locations on the die; and    said steps of grinding the surface of said packaged die are directly followed by polishing the ground surface of the packaged die.    
     
     
         5 . The method of  claim 4 , further comprising the act of mounting the packaged die to a lapping puck prior to the act of mounting the packaged die on the support.  
     
     
         6 . The method of  claim 5 , wherein the packaged die is mounted to the lapping puck using wax.  
     
     
         7 . The method of  claim 6 , wherein the wax has a melting point of less than 45 C.  
     
     
         8 . The method of  claim 4 , wherein media used in the act of grinding comprises two grades of particles.  
     
     
         9 . The method of  claim 4 , wherein the act of measuring includes using an optical tool selected from a group consisting of a reflectance spectrometer, a confocal microscope, and an ellipsometer.  
     
     
         10 . The method of  claim 9 , wherein the optical tool is a reflectance spectrometer, operating at NIR spectral range.  
     
     
         11 . The method of  claim 4 , further comprising the act of: 
 removing at least a portion of a lid from the die package prior to the act of mounting on the support.    
     
     
         12 . The method of  claim 4  further comprising the acts of: 
 heating the die; and  
 allowing the die to cool, prior to performing the further grinding and polishing.  
 
     
     
         13 . The method of  claim 12 , wherein the die is heated to a temperature ranging from about 40 to about 60 degrees Celsius.  
     
     
         14 . The method of  claim 12 , wherein the heating of the die is performed by placing the packaged die in heated wax.  
     
     
         15 . The method of  claim 4 , wherein the predetermined thickness is less than about 10 microns.  
     
     
         16 . The method of  claim 4 , further comprising de-warping the die.  
     
     
         17 . An integrated circuit having a die thinned according to the method of  claim 4 .  
     
     
         18 . An integrated circuit having a die thinned according to the method of  claim 12 .  
     
     
         19 . The method of  claim 1 , wherein said step of contacting a region of the surface of the packaged die to a thinning medium to thin at least a portion of the die to a thickness greater than the predetermined thickness is accomplished using a method selected from the group consisting of: mechanical milling, laser etching, FIB etching, electron beam etching.  
     
     
         20 . The method of  claim 19 , wherein said at least a portion of the die is less than the entire die.  
     
     
         21 . The method of  claim 20 , wherein said steps of measuring the thickness of the packaged die and of measuring the thickness of the thinned portion of the packaged die include using an optical tool selected from a group consisting of a reflectance spectrometer, a confocal microscope, and an ellipsometer.  
     
     
         22 . The method of  claim 21 , wherein said steps of measuring the thickness of the packaged die and of measuring the thickness of the thinned portion of the packaged die are performed in situ.  
     
     
         23 . An integrated circuit having a die thinned according to the method of  claim 21.