Semiconductor device and method for manufacturing semiconductor device
In a top-gate transistor in which an oxide semiconductor film, a gate insulating film, a gate electrode layer, and a silicon nitride film are stacked in this order and the oxide semiconductor film includes a channel formation region, nitrogen is added to regions of part of the oxide semiconductor film and the regions become low-resistance regions by forming a silicon nitride film over and in contact with the oxide semiconductor film. A source and drain electrode layers are in contact with the low-resistance regions. A region of the oxide semiconductor film, which does not contact the silicon nitride film (that is, a region overlapping with the gate insulating film and the gate electrode layer) becomes the channel formation region.
1. A method for manufacturing a semiconductor device comprising the steps of:
forming a gate electrode layer over an oxide semiconductor film with a gate insulating film therebetween; and
forming a silicon nitride film over the oxide semiconductor film, the gate insulating film, and the gate electrode layer so that the silicon nitride film is in contact with a first region of the oxide semiconductor film and nitrogen is added to the first region during the forming of the silicon nitride film,
wherein the oxide semiconductor film comprises a crystal,
wherein the silicon nitride film is formed by using a deposition gas comprising silane, nitrogen, and ammonia, and
wherein a flow ratio of ammonia to nitrogen in the deposition gas is less than or equal to 0.02.
2. The method for manufacturing a semiconductor device according to claim 1 ,
wherein the first region is a low-resistance region and is adjacent to a channel formation region of the oxide semiconductor film.
3. The method for manufacturing a semiconductor device according to claim 1 , further comprising the step of adding phosphorus or boron to the oxide semiconductor film with the gate electrode layer used as a mask after the gate electrode layer is formed.
4. The method for manufacturing a semiconductor device according to claim 1 , further comprising the step of performing heat treatment after the silicon nitride film is formed.
5. A method for manufacturing a semiconductor device comprising the steps of:
forming an oxide semiconductor film;
forming an insulating film over the oxide semiconductor film;
forming a gate electrode layer over the insulating film;
forming a gate insulating film by etching the insulating film using the gate electrode layer as a mask; and
forming a silicon nitride film over the oxide semiconductor film, the gate insulating film, and the gate electrode layer so that the silicon nitride film is in contact with a first region of the oxide semiconductor film and nitrogen is added to the first region during the forming of the silicon nitride film,
wherein the silicon nitride film is formed by using a deposition gas comprising silane, nitrogen, and ammonia, and
wherein a flow ratio of ammonia to nitrogen in the deposition gas is less than or equal to 0.02.
6. The method for manufacturing a semiconductor device according to claim 5 ,
wherein the first region is a low-resistance region and is adjacent to a channel formation region of the oxide semiconductor film.
7. The method for manufacturing a semiconductor device according to claim 5 , further comprising the step of adding phosphorus or boron to the oxide semiconductor film with the gate electrode layer used as a mask after the gate electrode layer is formed.
8. The method for manufacturing a semiconductor device according to claim 5 , further comprising the step of performing heat treatment after the silicon nitride film is formed.
9. The method for manufacturing a semiconductor device according to claim 1 , further comprising the steps of:
forming a first opening and a second opening in the silicon nitride film; and
forming a first electrode layer and a second electrode layer over the oxide semiconductor film and the silicon nitride film.