Semiconductor device and method for manufacturing the same

Abstract

An object is to provide a high reliable semiconductor device including a thin film transistor having stable electric characteristics. In a method for manufacturing a semiconductor device including a thin film transistor in which an oxide semiconductor film is used for a semiconductor layer including a channel formation region, heat treatment (which is for dehydration or dehydrogenation) is performed so as to improve the purity of the oxide semiconductor film and reduce impurities such as moisture. Besides impurities such as moisture existing in the oxide semiconductor film, heat treatment causes reduction of impurities such as moisture existing in the gate insulating layer and those in interfaces between the oxide semiconductor film and films which are provided over and below the oxide semiconductor film and are in contact with the oxide semiconductor film.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising an oxide semiconductor layer,
 wherein the oxide semiconductor layer comprises a channel formation region, and   wherein a hydrogen concentration in the channel formation region is 1×10 20  cm −3  or lower.   
     
     
         3 . The semiconductor device according to  claim 2 , wherein the oxide semiconductor layer comprises indium and zinc. 
     
     
         4 . The semiconductor device according to  claim 2 , wherein the hydrogen concentration in the channel formation region is obtained by secondary ion mass spectrometry. 
     
     
         5 . The semiconductor device according to  claim 2 , wherein the hydrogen concentration in the channel formation region is an average value of the hydrogen concentration in the channel formation region. 
     
     
         6 . The semiconductor device according to  claim 2 , further comprising an oxide insulating film over and in contact with the oxide semiconductor layer. 
     
     
         7 . A semiconductor device comprising an oxide semiconductor layer,
 wherein the oxide semiconductor layer comprises a channel formation region, and   wherein a hydrogen concentration in the channel formation region is 3×10 20  cm −3  or lower.   
     
     
         8 . The semiconductor device according to  claim 7 , wherein the oxide semiconductor layer comprises indium and zinc. 
     
     
         9 . The semiconductor device according to  claim 7 , wherein the hydrogen concentration in the channel formation region is obtained by secondary ion mass spectrometry. 
     
     
         10 . The semiconductor device according to  claim 7 , wherein the hydrogen concentration in the channel formation region is an average value of the hydrogen concentration in the channel formation region. 
     
     
         11 . The semiconductor device according to  claim 7 , further comprising an oxide insulating film over and in contact with the oxide semiconductor layer. 
     
     
         12 . A semiconductor device comprising an oxide semiconductor layer,
 wherein the oxide semiconductor layer comprises a channel formation region,   wherein a hydrogen concentration in the channel formation region is 3×10 20  cm −3  or lower, and   wherein the oxide semiconductor layer comprises a crystal.   
     
     
         13 . The semiconductor device according to  claim 12 , wherein the oxide semiconductor layer comprises indium and zinc. 
     
     
         14 . The semiconductor device according to  claim 12 , wherein the hydrogen concentration in the channel formation region is obtained by secondary ion mass, spectrometry. 
     
     
         15 . The semiconductor device according to  claim 12 , wherein the hydrogen concentration in the channel formation region is an average value of the hydrogen concentration in the channel formation region. 
     
     
         16 . The semiconductor device according to  claim 12 , further comprising an oxide insulating film over and in contact with the oxide semiconductor layer.