Methods and structures for preparing single crystal silicon wafers for use as substrates for epitaxial growth of crack-free gallium nitride films and devices

Abstract

This document describes the fabrication and use of ceramic stabilizing layer fabricated right on the product silicon wafer to facilitate its use as a substrate for fabrication of gallium nitride films. A ceramic layer is formed and then attached to a single crystal silicon substrate to form a composite silicon substrate that has coefficient of thermal expansion comparable with GaN. The composite silicon substrates prepared by this invention are uniquely suited for use as growth substrates for crack-free gallium nitride films, benefitting from compressive stresses produced by choosing a ceramic having a desired higher coefficient thermal expansion than those of silicon and gallium nitride.

What is claimed is: 
     
         1 . A method comprising
 providing a single crystal silicon substrate,
 wherein the silicon substrate comprises a first side and a second side; 
   applying a paste on the first side of the silicon substrate;   sintering the paste to solidify the paste,
 wherein the solidified paste has coefficient of thermal expansion (CTE) higher than that of silicon. 
   
     
     
         2 . A method as in  claim 1  wherein the second side of the silicon substrate comprises a (111) crystallographic surface. 
     
     
         3 . A method as in  claim 1  wherein the thickness of the silicon substrate is less than 50 microns. 
     
     
         4 . A method as in  claim 1  further comprising
 applying an adhesive to the first side of the silicon substrate before applying the paste. 
 
     
     
         5 . A method as in  claim 1  the paste comprises a refractory metal, ceramic, a powder of ceramic, glass, metal, or a mixture thereof. 
     
     
         6 . A method as in  claim 1  wherein the paste comprises an adhesive additive. 
     
     
         7 . A method as in  claim 1  wherein the sintering process is between 850 and 950 C. 
     
     
         8 . A method as in  claim 1  wherein the sintering process is between 800 and 1200 C. 
     
     
         9 . A method as in  claim 1  wherein the silicon substrate and the solidified paste form a composite substrate, and wherein the effective CTE of the composite substrate is higher than that of GaN. 
     
     
         10 . A method comprising
 providing a single crystal silicon substrate,
 wherein the silicon substrate comprises a first side and a second side; 
   placing the silicon substrate in a deposition chamber;   depositing a layer on the first side of the silicon substrate in vacuum,
 wherein the layer has coefficient of thermal expansion (CTE) higher than that of silicon. 
   
     
     
         11 . A method as in  claim 10  the layer comprises a refractory metal, ceramic, glass, metal, or a mixture thereof. 
     
     
         12 . A method as in  claim 10  wherein the silicon substrate and the deposited layer form a composite substrate, and wherein the effective CTE of the composite substrate is higher than that of GaN. 
     
     
         13 . A method comprising
 providing a single crystal silicon substrate,
 wherein the silicon substrate comprises a first side and a second side; 
   applying a slurry on the first side of the silicon substrate;   sintering the slurry to solidify the slurry,
 wherein the solidified slurry has coefficient of thermal expansion (CTE) higher than that of silicon. 
   
     
     
         14 . A method as in  claim 13  wherein the thickness of the silicon substrate is less than 50 microns. 
     
     
         15 . A method as in  claim 13  further comprising
 applying an adhesive to the first side of the silicon substrate before applying the slurry. 
 
     
     
         16 . A method as in  claim 13  the paste comprises a refractory metal, ceramic, a powder of ceramic, glass, metal, or a mixture thereof. 
     
     
         17 . A method as in  claim 13  wherein the slurry comprises an adhesive additive. 
     
     
         18 . A method as in  claim 13  wherein the sintering process is between 850 and 950 C. 
     
     
         19 . A method as in  claim 13  wherein the sintering process is between 800 and 1200 C. 
     
     
         20 . A method as in  claim 13  wherein the silicon substrate and the solidified slurry form a composite substrate, and wherein the effective CTE of the composite substrate is higher than that of GaN.