Semiconductor device and method for manufacturing the same

Abstract

An object is to provide a method for manufacturing a highly reliable semiconductor device which includes a thin film transistor using an oxide semiconductor and having stable electric characteristics. In manufacture of a semiconductor device in which an oxide semiconductor is used for a channel formation region, after an oxide semiconductor film is formed, a conductive film including a metal, a metal compound, or an alloy that can absorb or adsorb moisture, a hydroxy group, or hydrogen is formed to overlap with the oxide semiconductor film with an insulating film provided therebetween. Then, heat treatment is performed in the state where the conductive film is exposed; in such a manner, activation treatment for removing moisture, oxygen, hydrogen, or the like adsorbed onto a surface of or in the conductive film is performed.

1 . A semiconductor device comprising:
 a gate electrode on an insulating surface;   a gate insulating film over the gate electrode;   an oxide semiconductor film over the gate insulating film;   a source electrode and a drain electrode over the oxide semiconductor film;   an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode and in contact with the oxide semiconductor film; and   a back gate electrode over the insulating film and overlapping with the gate electrode and the oxide semiconductor film,   wherein the back gate electrode includes a hydrogen absorbing alloy.   
     
     
         2 . The semiconductor device according to  claim 1 , wherein the hydrogen absorbing alloy is at least one of LaNi 5 , Ti—Mn-based alloy, a Ti—Cr-based alloy, a Zr—Mn-based alloy, a Ti—V—Mn-based alloy, Mg 2 Ni, Mg 2 Cu, and Ti 2 Ni. 
     
     
         3 . The semiconductor device according to  claim 1 , wherein the insulating film is an oxide insulating film. 
     
     
         4 . The semiconductor device according to  claim 1 , further comprising an insulating film over the back gate electrode. 
     
     
         5 . A semiconductor device comprising:
 a gate electrode on an insulating surface;   a gate insulating film over the gate electrode;   a source electrode and a drain electrode over the gate insulating film;   an oxide semiconductor film over the source electrode and the drain electrode;   an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode and in contact with the oxide semiconductor film; and   a back gate electrode over the insulating film and overlapping with the gate electrode and the oxide semiconductor film,   wherein the back gate electrode includes a hydrogen absorbing alloy.   
     
     
         6 . The semiconductor device according to  claim 5 , wherein the hydrogen absorbing alloy is at least one of LaNi 5 , Ti—Mn-based alloy, a Ti—Cr-based alloy, a Zr—Mn-based alloy, a Ti—V—Mn-based alloy, Mg 2 Ni, Mg 2 Cu, and Ti 2 Ni. 
     
     
         7 . The semiconductor device according to  claim 5 , wherein the insulating film is an oxide insulating film. 
     
     
         8 . The semiconductor device according to  claim 5 , further comprising an insulating film over the back gate electrode. 
     
     
         9 . A semiconductor device comprising:
 a gate electrode on an insulating surface;   a gate insulating film over the gate electrode;   an oxide semiconductor film over the gate insulating film;   a channel protective film over the oxide semiconductor film;   a source electrode and a drain electrode over the oxide semiconductor film;   an insulating film over the channel protective film, the source electrode, and the drain electrode; and   a back gate electrode over the insulating film and overlapping with the gate electrode and the oxide semiconductor film,   wherein the back gate electrode includes a hydrogen absorbing alloy.   
     
     
         10 . The semiconductor device according to  claim 9 , wherein the hydrogen absorbing alloy is at least one of LaNi 5 , Ti—Mn-based alloy, a Ti—Cr-based alloy, a Zr—Mn-based alloy, a Ti—V—Mn-based alloy, Mg 2 Ni, Mg 2 Cu, and Ti 2 Ni. 
     
     
         11 . The semiconductor device according to  claim 9 , wherein the insulating film is an oxide insulating film 
     
     
         12 . The semiconductor device according to  claim 9 , further comprising an insulating film over the back gate electrode.