Semiconductor device and method of fabricating semiconductor device

Abstract

A method of fabricating a semiconductor device may form a nitride semiconductor layer on a substrate, form a first insulator layer on the nitride semiconductor layer by steam oxidation of ALD, form a second insulator layer on the first insulator layer by oxygen plasma oxidation of ALD, form a gate electrode on the second insulator layer, and form a source and drain electrodes on the nitride semiconductor layer. The nitride semiconductor layer may include a first semiconductor layer on the substrate, and a second semiconductor layer on the first semiconductor layer.

What is claimed is: 
     
         1 . A semiconductor device comprising:
 a nitride semiconductor layer formed on a substrate;   an insulator formed on the nitride semiconductor layer;   a gate electrode formed on the insulator layer; and   a source electrode and a drain electrode in contact with the nitride semiconductor layer,   wherein the nitride semiconductor layer includes a first semiconductor layer formed on the substrate, and a second semiconductor layer formed on the first semiconductor layer,   wherein the insulator layer includes a first insulator layer formed on the second semiconductor layer, and a second insulator layer formed on the first insulator layer, and   wherein the second insulator layer has a density higher than that of the first insulator layer.   
     
     
         2 . The semiconductor device as claimed in  claim 1 , wherein the nitride semiconductor layer further includes a third semiconductor layer formed on the second semiconductor layer. 
     
     
         3 . A semiconductor device comprising:
 a nitride semiconductor layer formed on a substrate;   an insulator formed on the nitride semiconductor layer;   a gate electrode formed on the insulator layer; and   a source electrode and a drain electrode formed on the nitride semiconductor layer,   wherein the nitride semiconductor layer includes a first semiconductor layer formed on the substrate, and a second semiconductor layer formed on the first semiconductor layer, and   wherein a ratio of oxygen atoms with respect to metal atoms included in the nitride semiconductor layer, in a vicinity of an interface between the nitride semiconductor layer and the insulator layer, is 0.4 or lower.   
     
     
         4 . The semiconductor device as claimed in  claim 3 , wherein the insulator layer is made of a material selected from a group consisting of an oxide, a nitride, and an oxynitride of any one or a combination of aluminum hafnium, silicon, and nickel. 
     
     
         5 . The semiconductor device as claimed in  claim 3 , wherein the insulator layer is made of aluminum oxide. 
     
     
         6 . The semiconductor device as claimed in  claim 5 , wherein a density of aluminum hydroxide included the insulator layer is 4% or lower. 
     
     
         7 . The semiconductor device as claimed in  claim 3 , wherein the nitride semiconductor layer further includes a third semiconductor layer formed on the second semiconductor layer. 
     
     
         8 . The semiconductor device as claimed in  claim 7 , wherein the third semiconductor layer is made of a material including GaN. 
     
     
         9 . The semiconductor device as claimed in  claim 8 , wherein the first semiconductor layer is made of a material including GaN. 
     
     
         10 . The semiconductor device as claimed in  claim 9 , wherein the second semiconductor layer is made of a material including AlGaN. 
     
     
         11 . The semiconductor device as claimed in  claim 3 , including HEMT (High Electron Mobility Transistor). 
     
     
         12 . A power supply unit comprising:
 the semiconductor device as claimed in  claim 3 .   
     
     
         13 . An amplifier comprising:
 the semiconductor device as claimed in  claim 3 .   
     
     
         14 . A method of fabricating a semiconductor device, comprising:
 forming a nitride semiconductor layer on a substrate;   forming a first insulator layer on the nitride semiconductor layer by steam oxidation of ALD (Atomic Layer Deposition) using H 2 O source gas, or by oxidation of ALD using O 3  source gas;   forming a second insulator layer on the first insulator layer by oxygen plasma oxidation of ALD using O 2  source gas;   forming a gate electrode on the second insulator layer; and   forming a source electrode and a drain electrode on the nitride semiconductor layer,   wherein the forming the nitride semiconductor layer includes forming a first semiconductor layer on the substrate, and forming a second semiconductor layer on the first semiconductor layer.   
     
     
         15 . The method as claimed in  claim 14 , wherein the forming the nitride semiconductor layer further includes forming a third semiconductor layer on the second semiconductor layer. 
     
     
         16 . The method as claimed in  claim 14 , further comprising:
 forming a recess in a region where the gate electrode is to be formed, by removing a part of the nitride semiconductor layer,   wherein the forming the recess is carried out after the forming the nitride semiconductor layer and before the forming the first insulator layer.   
     
     
         17 . The method as claimed in  claim 14 , wherein the forming the first insulator layer forms a first aluminum oxide layer as the first insulator layer, and the forming the second insulator layer forms a second aluminum oxide layer as the second insulator layer. 
     
     
         18 . The method as claimed in  claim 17 , wherein the forming the first insulator layer forms the first insulator layer by steam oxidation of ALD using trimethylaluminum (TMA) and H 2 O as source gases. 
     
     
         19 . The method as claimed in  claim 17 , wherein the forming the second insulator layer forms the second insulator layer by oxygen plasma oxidation of ALD using trimethylaluminum (TMA) and O 2  or O 3  as source gases. 
     
     
         20 . The method as claimed in  claim 14 , further comprising:
 performing a heat treatment after the forming the second insulator layer, at a temperature of 700° C. or higher and 800° C. or lower.