Semiconductor device

Abstract

A semiconductor device in which an increase in oxygen vacancies in an oxide semiconductor layer can be suppressed is provided. A semiconductor device with favorable electrical characteristics is provided. A highly reliable semiconductor device is provided. A semiconductor device includes an oxide semiconductor layer in a channel formation region, and by the use of an oxide insulating film below and in contact with the oxide semiconductor layer and a gate insulating film over and in contact with the oxide semiconductor layer, oxygen of the oxide insulating film or the gate insulating film is supplied to the oxide semiconductor layer. Further, a conductive nitride is used for a metal film of a source electrode layer and a drain electrode layer, whereby diffusion of oxygen to the metal film is suppressed.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising:
 an oxide semiconductor layer over a substrate;   an electrode layer over and in contact with the oxide semiconductor layer, the electrode layer comprising titanium nitride;   a gate insulating film over the oxide semiconductor layer and the electrode layer; and   a gate electrode layer over the gate insulating film, the gate electrode layer overlapping the oxide semiconductor layer.   
     
     
         3 . The semiconductor device according to  claim 2 , further comprising a protective insulating film over the gate electrode layer,
 wherein the protective insulating film comprises silicon nitride.   
     
     
         4 . The semiconductor device according to  claim 2 ,
 wherein the oxide semiconductor layer comprises a crystal, and   wherein a c-axis of the crystal is parallel to a normal vector of a surface of the oxide semiconductor layer.   
     
     
         5 . A semiconductor device comprising:
 an oxide semiconductor layer over a substrate;   a first electrode layer over and in contact with the oxide semiconductor layer;   a second electrode layer over the first electrode layer, the second electrode layer comprising titanium nitride;   a gate insulating film over the oxide semiconductor layer and the second electrode layer; and   a gate electrode layer over the gate insulating film, the gate electrode layer overlapping the oxide semiconductor layer,   wherein the second electrode layer is in contact with a side surface of the first electrode layer and a top surface of the oxide semiconductor layer.   
     
     
         6 . The semiconductor device according to  claim 5 , wherein the first electrode layer comprises at least one selected from Al, Cr, Cu, Ta, Ti, Mo, and W. 
     
     
         7 . The semiconductor device according to  claim 5 , wherein an end portion of the first electrode layer has a step. 
     
     
         8 . The semiconductor device according to  claim 5 , further comprising a protective insulating film over the gate electrode layer,
 wherein the protective insulating film comprises silicon nitride.   
     
     
         9 . The semiconductor device according to  claim 5 ,
 wherein the oxide semiconductor layer comprises a crystal, and   wherein a c-axis of the crystal is parallel to a normal vector of a surface of the oxide semiconductor layer.   
     
     
         10 . A semiconductor device comprising:
 an oxide insulating film over a substrate;   an oxide semiconductor layer over the oxide insulating film;   a first electrode layer over and in contact with the oxide semiconductor layer;   a second electrode layer over the first electrode layer, the second electrode layer comprising titanium nitride;   a gate insulating film over the oxide semiconductor layer and the second electrode layer; and   a gate electrode layer over the gate insulating film, the gate electrode layer overlapping the oxide semiconductor layer,   wherein the second electrode layer is in contact with a side surface of the first electrode layer, a top surface of the oxide semiconductor layer and a top surface of the oxide insulating film.   
     
     
         11 . The semiconductor device according to  claim 10 , wherein the first electrode layer comprises at least one selected from Al, Cr, Cu, Ta, Ti, Mo, and W. 
     
     
         12 . The semiconductor device according to  claim 10 , wherein an end portion of the first electrode layer has a step. 
     
     
         13 . The semiconductor device according to  claim 10 , further comprising a protective insulating film over the gate electrode layer,
 wherein the protective insulating film comprises silicon nitride.   
     
     
         14 . The semiconductor device according to  claim 10 ,
 wherein the oxide semiconductor layer comprises a crystal, and   wherein a c-axis of the crystal is parallel to a normal vector of a surface of the oxide semiconductor layer.   
     
     
         15 . The semiconductor device according to  claim 10 , wherein the gate insulating film is in contact with a side surface of the second electrode layer, the top surface of the oxide semiconductor layer and the top surface of the oxide insulating film. 
     
     
         16 . The semiconductor device according to  claim 10 , wherein the first electrode layer is in contact with the top surface of the oxide insulating film.