Semiconductor device and method for manufacturing the same

Abstract

A highly reliable semiconductor device which includes a transistor including an oxide semiconductor is provided. In a semiconductor device including a bottom-gate transistor including an oxide semiconductor layer, a stacked layer of an insulating layer and a metal film is provided in contact with the oxide semiconductor layer. Oxygen doping treatment is performed in a manner such that oxygen is introduced into the insulating layer and the metal film from a position above the metal film. Thus, a region containing oxygen in excess of the stoichiometric composition is formed in the insulating layer, and the metal film is oxidized to form a metal oxide film. Further, resistivity of the metal oxide film is greater than or equal to 1×10 10 Ωm and less than or equal to 1×10 19 Ωm.

What is claimed is: 
     
         1 . A method for manufacturing a semiconductor device comprising the steps of:
 forming a gate electrode layer;   forming a gate insulating layer over the gate electrode layer;   forming an oxide semiconductor layer to overlap with the gate electrode layer with the gate insulating layer interposed therebetween;   forming a source electrode layer and a drain electrode layer over the oxide semiconductor layer;   forming an insulating layer over the source electrode layer and the drain electrode layer;   forming a metal film over the insulating layer; and   adding oxygen to the metal film and the insulating layer so that a metal oxide film having a resistivity greater than or equal to 1×10′ Ωm and less than or equal to 1×10 19  Ωm is formed over the insulating layer.   
     
     
         2 . The method for manufacturing a semiconductor device according to  claim 1 , further comprising the step of performing a heat treatment on the insulating layer before forming the metal film so that water or hydrogen in the insulating layer is reduced. 
     
     
         3 . The method for manufacturing a semiconductor device according to  claim 1 ,
 wherein the metal film is an aluminum film, and   wherein the metal oxide film is an aluminum oxide film.   
     
     
         4 . The method for manufacturing a semiconductor device according to  claim 1 , further comprising the step of performing a heat treatment on the insulating layer after adding oxygen to the metal film and the insulating layer so that oxygen is supplied from the insulating layer to the oxide semiconductor layer. 
     
     
         5 . A method for manufacturing a semiconductor device comprising the steps of:
 forming a gate electrode layer;   forming a gate insulating layer over the gate electrode layer;   forming an oxide semiconductor layer to overlap with the gate electrode layer with the gate insulating layer interposed therebetween;   forming an insulating layer over and in contact with the oxide semiconductor layer;   forming a metal film over the insulating layer;   adding oxygen to the metal film and the insulating layer so that a metal oxide film having a resistivity greater than or equal to 1×10′ Ωm and less than or equal to 1×10 19  Ωm is formed over the insulating layer;   forming a first opening and a second opening in the insulating layer; and   forming a source electrode layer in contact with the oxide semiconductor layer through the first opening and a drain electrode layer in contact with the oxide semiconductor layer through the second opening.   
     
     
         6 . The method for manufacturing a semiconductor device according to  claim 5 , further comprising the step of performing a heat treatment on the insulating layer before forming the metal film so that water or hydrogen in the insulating layer is reduced. 
     
     
         7 . The method for manufacturing a semiconductor device according to  claim 5 ,
 wherein the metal film is an aluminum film, and   wherein the metal oxide film is an aluminum oxide film.   
     
     
         8 . The method for manufacturing a semiconductor device according to  claim 5 , further comprising the step of performing a heat treatment on the insulating layer after adding oxygen to the metal film and the insulating layer so that oxygen is supplied from the insulating layer to the oxide semiconductor layer.