Semiconductor device, display device including the semiconductor device, and an electronic device including the semiconductor device

Abstract

A semiconductor device that includes a transistor is provided. The transistor includes a first conductive film that functions as a first gate electrode, a first gate insulating film, a first oxide semiconductor film that includes a channel region, a second gate insulating film, and a second oxide semiconductor film and a second conductive film that function as a second gate electrode. The second oxide semiconductor film includes a region higher in carrier density than the first oxide semiconductor film. The second conductive film includes a region in contact with the first conductive film.

1 . A method for manufacturing a semiconductor device, comprising:
 forming a first gate electrode;   forming a first insulating film over the first gate electrode;   forming a first oxide semiconductor film over the first insulating film;   forming a second insulating film over the first oxide semiconductor film;   forming a second oxide semiconductor film over the second insulating film;   forming an opening reaching the first gate electrode in the first insulating film, the second insulating film, and the second oxide semiconductor film;   forming a second gate electrode in direct contact with the first gate electrode via the opening;   adding an impurity to the first oxide semiconductor film using the second gate electrode as a mask to form source and drain regions sandwiching a channel region in the first oxide semiconductor film; and   forming a third insulating film over the first oxide semiconductor film, the second oxide semiconductor film, and the second gate electrode.   
     
     
         2 . The method according to  claim 1 , wherein the second oxide semiconductor film includes a region having a higher carrier density than the channel region. 
     
     
         3 . The method according to  claim 1 , further comprising:
 forming second and third openings reaching the first oxide semiconductor film in the third insulating film; and   forming source and drain electrodes electrically connected to the source and drain regions via the second and third openings, respectively.   
     
     
         4 . The method according to  claim 1 , wherein:
 the second oxide semiconductor film contains In, Zn, and M (M is Al, Ga, Y, or Sn), and   the second oxide semiconductor film includes a region where a content of the In is higher than a content of the M.   
     
     
         5 . The method according to  claim 1 , wherein:
 the first oxide semiconductor film contains In, Zn, and M (M is Al, Ga, Y, or Sn), and   the first oxide semiconductor film includes a region where a content of the In is higher than a content of the M.   
     
     
         6 . The method according to  claim 1 , wherein the third insulating film contains at least one of nitrogen and hydrogen. 
     
     
         7 . The method according to  claim 1 , wherein the first oxide semiconductor film includes a crystal part having c-axis alignment. 
     
     
         8 . A method for manufacturing a semiconductor device, comprising:
 forming a first gate electrode;   forming a first insulating film over the first gate electrode;   forming a first oxide semiconductor film over the first insulating film;   forming a second insulating film over the first oxide semiconductor film;   forming a second oxide semiconductor film over the second insulating film;   forming an opening reaching the first gate electrode in the first insulating film, the second insulating film, and the second oxide semiconductor film;   forming a second gate electrode in direct contact with the first gate electrode via the opening;   adding an impurity to the first oxide semiconductor film using the second gate electrode as a mask to form source and drain regions sandwiching a channel region in the first oxide semiconductor film; and   forming a third insulating film over the first oxide semiconductor film, the second oxide semiconductor film, and the second gate electrode,   wherein the impurity element is any one of hydrogen, carbon, silicon, a transition metal element, argon, and nitrogen, and   wherein the transition element decreases a crystallinity of the source and drain regions.   
     
     
         9 . The method according to  claim 8 , wherein the second oxide semiconductor film includes a region having a higher carrier density than the channel region. 
     
     
         10 . The method according to  claim 8 , further comprising:
 forming second and third openings reaching the first oxide semiconductor film in the third insulating film; and   forming source and drain electrodes electrically connected to the source and drain regions via the second and third openings, respectively.   
     
     
         11 . The method according to  claim 8 , wherein:
 the second oxide semiconductor film contains In, Zn, and M (M is Al, Ga, Y, or Sn), and   the second oxide semiconductor film includes a region where a content of the In is higher than a content of the M.   
     
     
         12 . The method according to  claim 8 , wherein:
 the first oxide semiconductor film contains In, Zn, and M (M is Al, Ga, Y, or Sn), and   the first oxide semiconductor film includes a region where a content of the In is higher than a content of the M.   
     
     
         13 . The method according to  claim 8 , wherein the third insulating film contains at least one of nitrogen and hydrogen. 
     
     
         14 . The method according to  claim 8 , wherein the first oxide semiconductor film includes a crystal part having c-axis alignment. 
     
     
         15 . A method for manufacturing a semiconductor device, comprising:
 forming a first electrode;   forming a first insulating film over the first electrode;   forming a first oxide semiconductor film over the first insulating film;   forming a second insulating film over the first oxide semiconductor film;   forming a second oxide semiconductor film over the second insulating film;   forming an opening reaching the first electrode in the first insulating film, the second insulating film, and the second oxide semiconductor film;   forming a second electrode in direct contact with the first electrode via the opening;   adding an impurity to the first oxide semiconductor film using the second electrode as a mask to form source and drain regions sandwiching a channel region in the first oxide semiconductor film; and   forming a third insulating film over the first oxide semiconductor film, the second oxide semiconductor film, and the second electrode,   wherein the addition of the impurity element either cuts a bond between a metal element and oxygen or bonds oxygen bonded to a metal element to the impurity element so as to form an oxygen vacancy.   
     
     
         16 . The method according to  claim 15 , wherein the second oxide semiconductor film includes a region having a higher carrier density than the channel region. 
     
     
         17 . The method according to  claim 15 , further comprising:
 forming second and third openings reaching the first oxide semiconductor film in the third insulating film; and   forming source and drain electrodes electrically connected to the source and drain regions via the second and third openings, respectively.   
     
     
         18 . The method according to  claim 15 , wherein:
 the second oxide semiconductor film contains In, Zn, and M (M is Al, Ga, Y, or Sn), and   the second oxide semiconductor film includes a region where a content of the In is higher than a content of the M.   
     
     
         19 . The method according to  claim 15 , wherein:
 the first oxide semiconductor film contains In, Zn, and M (M is Al, Ga, Y, or Sn), and   the first oxide semiconductor film includes a region where a content of the In is higher than a content of the M.   
     
     
         20 . The method according to  claim 15 , wherein the third insulating film contains at least one of nitrogen and hydrogen.