Thin-film transitor and method for manufacturing the same

Abstract

According to one embodiment, a thin-film transistor comprises an oxide semiconductor layer formed on a part of a substrate, a first gate insulator film of a silicon dioxide film formed on the oxide semiconductor layer and by the CVD method with a silane-based source gas, a second gate insulator film of a silicon dioxide film formed on the first gate insulator film by the CVD method with a TEOS source gas, and a gate electrode formed on the second gate insulator film.

What is claimed is: 
     
         1 . A thin-film transistor comprising:
 an oxide semiconductor layer formed on a part of a substrate;   a first gate insulator film of a silicon dioxide film formed on the oxide semiconductor layer and the substrate by the CVD method with a silane-based source gas;   a second gate insulator film of a silicon dioxide film formed on the first gate insulator film by the CVD method with a TEOS source gas; and   a gate electrode formed on the second gate insulator film.   
     
     
         2 . The thin-film transistor of  claim 1 , wherein the oxide semiconductor layer is an oxide of an alloy of indium, gallium and zinc (IGZO). 
     
     
         3 . A method for manufacturing a thin-film transistor comprising:
 forming an oxide semiconductor layer on a part of a substrate;   forming a first gate insulator film of a silicon dioxide film on the oxide semiconductor layer and the substrate by the CVD method with a silane-based source gas;   forming a second gate insulator film of a silicon dioxide film on the first gate insulator film by the CVD method with a TEOS source gas; and   forming a gate electrode on the second gate insulator film.   
     
     
         4 . The method of  claim 3 , wherein gas consisting mainly of SiH 4  and N 2 O is used as the silane-based source gas. 
     
     
         5 . The method of  claim 3 , wherein an oxide of an alloy of indium, gallium and zinc (IGZO) is used as the oxide semiconductor layer. 
     
     
         6 . The method of  claim 3 , wherein the forming of the oxide semiconductor layer includes forming the oxide semiconductor layer on the substrate and subsequently processing the oxide semiconductor layer by wet etching into a shape of an island. 
     
     
         7 . A method for manufacturing a thin-film transistor comprising:
 forming an oxide semiconductor layer on a part of a substrate;   forming a gate insulator film of a silicon dioxide film on the oxide semiconductor layer and the substrate by performing a surface treatment with oxygen plasma and by forming a film by the CVD method with a TEOS source gas; and   forming a gate electrode on the gate insulator film.   
     
     
         8 . The method of  claim 7 , wherein an oxide of an alloy of indium, gallium and zinc (IGZO) is used as the oxide semiconductor layer. 
     
     
         9 . The method of  claim 7 , wherein the forming of the oxide semiconductor layer includes forming the oxide semiconductor layer on the substrate and subsequently processing the oxide semiconductor layer by wet etching into a shape of an island. 
     
     
         10 . The method of  claim 7 , wherein the forming of the gate insulator film includes performing the surface treatment with the oxygen plasma on the oxide semiconductor layer and subsequently forming the gate insulator film by the CVD method. 
     
     
         11 . The method of  claim 10 , wherein an oxide of an alloy of indium, gallium and zinc (IGZO) is used as the oxide semiconductor layer. 
     
     
         12 . The method of  claim 10 , wherein the forming of the oxide semiconductor layer includes forming the oxide semiconductor layer entirely on the substrate and processing the oxide semiconductor layer by wet etching into a shape of an island. 
     
     
         13 . The method of  claim 7 , wherein the forming of the gate insulator film includes performing the surface treatment with the oxygen plasma on the oxide semiconductor layer and forming the gate insulator film by the CVD method simultaneously. 
     
     
         14 . The method of  claim 13 , wherein an oxide of an alloy of indium, gallium and zinc (IGZO) is used as the oxide semiconductor layer. 
     
     
         15 . The method of  claim 13 , wherein the forming of the oxide semiconductor layer includes forming the oxide semiconductor layer entirely on the substrate and subsequently processing the oxide semiconductor layer by wet etching into a shape of an island.