Nucleation of Aluminum Nitride on a Silicon Substrate Using an Ammonia Preflow

Abstract

A silicon wafer used in manufacturing crystalline GaN for light emitting diodes (LEDs) includes a silicon substrate, a buffer layer of aluminum nitride (AlN) and an upper layer of GaN. The silicon wafer has a diameter of at least 200 millimeters and an Si(111)1×1 surface. The AlN buffer layer overlies the Si(111) surface. The GaN upper layer is disposed above the buffer layer. Across the entire wafer substantially no aluminum atoms of the AlN are present in a bottom most plane of atoms of the AlN, and across the entire wafer substantially only nitrogen atoms of the AlN are present in the bottom most plane of atoms of the AlN. A method of making the AlN buffer layer includes preflowing a first amount of ammonia equaling less than 0.01% by volume of hydrogen flowing through a chamber before flowing trimethylaluminum and then a subsequent amount of ammonia through the chamber.

1 . An apparatus comprising:
 a substrate of silicon (Si), wherein the substrate is a wafer with a diameter of at least 200 millimeters, and wherein the substrate has an Si(111) surface;   a buffer layer of aluminum nitride (AlN) overlying the Si(111) surface of the substrate; and   an upper layer of gallium nitride (GaN) above the buffer layer, wherein across the entire wafer substantially no aluminum atoms of the aluminum nitride are present in a bottom most plane of atoms of the aluminum nitride, and wherein across the entire wafer substantially only nitrogen atoms of the aluminum nitride are present in the bottom most plane of atoms of the aluminum nitride.   
     
     
         2 . The apparatus of  claim 1 , wherein no layer of SiNx is present between the substrate and the buffer layer. 
     
     
         3 . The apparatus of  claim 1 , wherein the Si(111) surface has a Si(111)1×1 structure and not a Si(111)7×7 structure. 
     
     
         4 . The apparatus of  claim 1 , wherein the silicon and aluminum nitride are oriented as AlN<0001>∥Si<111>. 
     
     
         5 . The apparatus of  claim 1 , wherein no amount of metallic aluminum is disposed between the substrate and the buffer layer. 
     
     
         6 . The apparatus of  claim 1 , further comprising:
 a second buffer layer comprising aluminum gallium nitride (Al x Ga 1-x N), wherein the second buffer layer of aluminum gallium nitride is disposed between the buffer layer of aluminum nitride and the upper layer of gallium nitride.   
     
     
         7 . The apparatus of  claim 1 , wherein the buffer layer of aluminum nitride (AlN) is between 205 to 250 nanometers thick. 
     
     
         8 . A method comprising:
 (a) heating a substrate of silicon (Si) to a temperature above 950° C. in a chamber;   (b) flowing hydrogen (H 2 ) through the chamber;   (c) flowing a first amount of ammonia (NH 3 ) through the chamber while the hydrogen is still flowing through the chamber, wherein the first amount of ammonia is less than 0.01% by volume of the hydrogen flowing through the chamber;   (d) flowing trimethylaluminum (Al 2 (CH 3 ) 6 ) through the chamber while the hydrogen is still flowing through the chamber; and   (e) flowing a subsequent amount of ammonia through the chamber while the trimethylaluminum is still flowing through the chamber, wherein the subsequent amount of ammonia is greater than 0.002% by volume of the hydrogen flowing through the chamber.   
     
     
         9 . The method of  claim 8 , wherein the flowing the first amount of ammonia through the chamber is performed for between thirty seconds to three minutes. 
     
     
         10 . The method of  claim 8 , wherein the substrate is a wafer having a surface, and wherein the first amount of ammonia does not exceed 0.006 cubic centimeters per minute over each square centimeter of the surface of the substrate. 
     
     
         11 . The method of  claim 8 , wherein the substrate is a wafer having a surface, and wherein the flowing the hydrogen through the chamber is performed by flowing between 106 and 118 cubic centimeters of hydrogen per minute over each square centimeter of the surface of the substrate. 
     
     
         12 . The method of  claim 8 , wherein the flowing the trimethylaluminum through the chamber is performed for between ten to twenty minutes. 
     
     
         13 . The method of  claim 8 , wherein trimethylaluminum flows through the chamber in an amount of about ninety micromoles per minute. 
     
     
         14 . The method of  claim 8 , wherein the temperature in the chamber during the flowing of hydrogen in (b) is above 1100° C., and wherein the temperature in the chamber during the flowing of the first amount of ammonia in (c) is between 1000° C. and 1050° C. 
     
     
         15 . An apparatus comprising:
 a substrate of silicon (Si), wherein the substrate is a wafer with a diameter greater than six inches, and wherein the substrate has an Si(111) surface;   an upper layer of gallium nitride (GaN) above the substrate, wherein there is a lattice mismatch between the Si(111) surface and the upper layer of gallium nitride; and   means for compensating for the lattice mismatch so as to enable the upper layer of gallium nitride to grow under reduced stress, wherein the means includes nitrogen atoms, and wherein across the entire wafer substantially only nitrogen atoms of the means form bonds to the Si(111) surface.   
     
     
         16 . The apparatus of  claim 15 , wherein no layer of another substance is present between the substrate and the means. 
     
     
         17 . The apparatus of  claim 15 , wherein the Si(111) surface has a Si(111)1×1 structure and not a Si(111)7×7 structure. 
     
     
         18 . The apparatus of  claim 15 , further comprising:
 a buffer layer comprising aluminum gallium nitride (Al x Ga 1-x N), wherein the buffer layer of aluminum gallium nitride is disposed between the means and the upper layer of gallium nitride.   
     
     
         19 . The apparatus of  claim 15 , wherein the means is a layer that is between 180 to 200 nanometers thick. 
     
     
         20 . The apparatus of  claim 15 , wherein the means is a single polarity material.