Semiconductor device

Abstract

An object is to prevent an impurity such as moisture and oxygen from being mixed into an oxide semiconductor and suppress variation in semiconductor characteristics of a semiconductor device in which an oxide semiconductor is used. Another object is to provide a semiconductor device with high reliability. A gate insulating film provided over a substrate having an insulating surface, a source and a drain electrode which are provided over the gate insulating film, a first oxide semiconductor layer provided over the source electrode and the drain electrode, and a source and a drain region which are provided between the source electrode and the drain electrode and the first oxide semiconductor layer are provided. A barrier film is provided in contact with the first oxide semiconductor layer.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising:
 a substrate;   a gate electrode layer over the substrate;   a gate insulating layer over the gate electrode layer;   a first oxide semiconductor layer over the gate insulating layer;   a source electrode layer and a drain electrode layer over the first oxide semiconductor layer; and   a barrier layer over and in contact with the first oxide semiconductor layer, the source electrode layer, and the drain electrode layer,   wherein a concentration of sodium in the first oxide semiconductor layer is less than or equal to 5×10 19  cm 3 .   
     
     
         3 . The semiconductor device according to  claim 2 , wherein the barrier layer includes one or more of an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and an aluminum nitride oxide film. 
     
     
         4 . The semiconductor device according to  claim 2 , wherein a thickness of the barrier layer is greater than or equal to 1 nm and less than or equal to 200 nm. 
     
     
         5 . The semiconductor device according to  claim 2 , wherein the gate insulating layer includes one or more of an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and an aluminum nitride oxide film. 
     
     
         6 . The semiconductor device according to  claim 2 , wherein the first oxide semiconductor layer includes indium, gallium, and zinc. 
     
     
         7 . The semiconductor device according to  claim 2 , wherein the first oxide semiconductor layer includes a crystal grain. 
     
     
         8 . The semiconductor device according to  claim 7 , wherein a diameter of the crystal grain is greater than or equal to 1 nm and less than or equal to 10 nm. 
     
     
         9 . The semiconductor device according to  claim 2 , wherein the first oxide semiconductor layer has a depression. 
     
     
         10 . The semiconductor device according to  claim 2 , further comprising:
 a second oxide semiconductor layer between the first oxide semiconductor layer and the source electrode layer, and   a third oxide semiconductor layer between the first oxide semiconductor layer and the drain electrode layer,   wherein each of the second oxide semiconductor layer and the third oxide semiconductor layer has higher conductivity than the first oxide semiconductor layer.   
     
     
         11 . The semiconductor device according to  claim 10 , wherein each of the second oxide semiconductor layer and the third oxide semiconductor layer includes indium, gallium, and zinc. 
     
     
         12 . A semiconductor device comprising:
 a substrate;   a gate electrode layer over the substrate;   a gate insulating layer over the gate electrode layer;   a first oxide semiconductor layer over the gate insulating layer;   a channel protective layer over and in contact with a part of the first oxide semiconductor layer;   a source electrode layer and a drain electrode layer over the first oxide semiconductor layer;   a barrier layer over and in contact with the channel protective layer, the source electrode layer, and the drain electrode layer,   wherein a concentration of sodium in the first oxide semiconductor layer is less than or equal to 5×10 19  cm 3 .   
     
     
         13 . The semiconductor device according to  claim 12 , wherein the barrier layer includes one or more of an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and an aluminum nitride oxide film. 
     
     
         14 . The semiconductor device according to  claim 12 , wherein a thickness of the barrier layer is greater than or equal to 1 nm and less than or equal to 200 nm. 
     
     
         15 . The semiconductor device according to  claim 12 , wherein the gate insulating layer includes one or more of an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and an aluminum nitride oxide film. 
     
     
         16 . The semiconductor device according to  claim 12 , wherein the first oxide semiconductor layer includes indium, gallium, and zinc. 
     
     
         17 . The semiconductor device according to  claim 12 , wherein the first oxide semiconductor layer includes a crystal grain. 
     
     
         18 . The semiconductor device according to  claim 17 , wherein a diameter of the crystal grain is greater than or equal to 1 nm and less than or equal to 10 nm. 
     
     
         19 . The semiconductor device according to  claim 12 , further comprising:
 a second oxide semiconductor layer between the first oxide semiconductor layer and the source electrode layer, and   a third oxide semiconductor layer between the first oxide semiconductor layer and the drain electrode layer,   wherein each of the second oxide semiconductor layer and the third oxide semiconductor layer has higher conductivity than the first oxide semiconductor layer.   
     
     
         20 . The semiconductor device according to  claim 19 , wherein each of the second oxide semiconductor layer and the third oxide semiconductor layer includes indium, gallium, and zinc.