Method for fabricating semiconductor device

Abstract

A method for fabricating a semiconductor device includes: forming a first film on a nitride semiconductor layer so as to contact the nitride semiconductor layer and have a thickness equal to or larger than 1 nm and equal to or smaller than 5 nm, the first film being made of silicon nitride having a composition ratio of silicon to nitrogen larger than 0.75, silicon oxide having a composition ratio of silicon to oxygen larger than 0.5, or aluminum; and forming a source electrode, a gate electrode and a drain electrode on the nitride semiconductor layer.

What is claimed is: 
     
         1 . A method for fabricating a semiconductor device comprising:
 forming a first film that contact a surface of the nitride semiconductor layer and have a thickness equal to or larger than 1 nm and equal to or smaller than 5 nm, the first film being made of silicon nitride having a composition ratio of silicon to nitrogen larger than 0.75, silicon oxide having a composition ratio of silicon to oxygen larger than 0.5, or aluminum; and   forming a source electrode, a gate electrode and a drain electrode on the nitride semiconductor layer.   
     
     
         2 . The method according to  claim 1 , further comprising forming a second film that contacts a surface of the first film, wherein the second film is substantially a stoichiometric composition and is made of one of silicon nitride, silicon oxide, aluminum oxide and aluminum nitride. 
     
     
         3 . The method according to  claim 1 , wherein the first film is silicon nitride, and the method further comprises forming of a second film composed of silicon nitride having a silicon composition smaller than the first film. 
     
     
         4 . The method according to  claim 2 , wherein a formation method of the first film is an atomic layer deposition method, and a formation method of the second film is an atomic layer deposition method. 
     
     
         5 . The method according to  claim 3 , wherein a formation method of the first film is an atomic layer deposition method, and a formation method of the second film is an atomic layer deposition method. 
     
     
         6 . The method according to  claim 2 , wherein the second film has a thickness that is equal to or larger than 20 nm and is equal to or smaller than 100 nm. 
     
     
         7 . The method according to  claim 3 , wherein the second film has a thickness that is equal to or larger than 20 nm and is equal to or smaller than 100 nm. 
     
     
         8 . The method according to  claim 1 , wherein the first film is composed of aluminum, and the method comprises forming a second film on the first film, a formation of the second film is performed in-situ after a formation of the first film. 
     
     
         9 . The method according to  claim 8 , wherein the formation of the first and second film is performed under an atomic layer deposition apparatus. 
     
     
         10 . The method according to  claim 1 , wherein the first film is formed between the source electrode and the gate electrode, and is between the gate electrode and the drain electrode. 
     
     
         11 . The method according to  claim 1 , wherein the first film is composed of silicon nitride, and the composition ratio of silicon to nitrogen of first film is larger than 0.8. 
     
     
         12 . The method according to  claim 1 , wherein the first film is composed of silicon nitride, and the composition ratio of silicon to nitrogen of first film is larger than 0.85. 
     
     
         13 . The method according to  claim 1 , wherein the first film is composed of silicon nitride, and the composition ratio of silicon to nitrogen of first film is larger than 0.9.