Semiconductor device and manufacturing method thereof

Abstract

Provided are a transistor which has electrical characteristics requisite for its purpose and uses an oxide semiconductor layer and a semiconductor device including the transistor. In the bottom-gate transistor in which at least a gate electrode layer, a gate insulating film, and the semiconductor layer are stacked in this order, an oxide semiconductor stacked layer including at least two oxide semiconductor layers whose energy gaps are different from each other is used as the semiconductor layer. Oxygen and/or a dopant may be added to the oxide semiconductor stacked layer.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising:
 an oxide stacked layer comprising a first oxide layer, a second oxide layer over the first oxide layer, and a third oxide layer over the second oxide layer;   a source electrode over the oxide stacked layer, the source electrode being in contact with at least a side surface of the second oxide layer; and   a drain electrode over the oxide stacked layer, the drain electrode being in contact with at least a side surface of the second oxide layer,   wherein energy at a bottom of a conduction band of the second oxide layer is lower than energy at a bottom of a conduction band of the first oxide layer and energy at a bottom of a conduction band of the third oxide layer,   wherein the second oxide layer comprises indium, and   wherein each of the first oxide layer and the third oxide layer comprises gallium.   
     
     
         3 . The semiconductor device according to  claim 2 ,
 wherein the source electrode is in contact with a side surface of the first oxide layer,   wherein the drain electrode is in contact with a side surface of the first oxide layer,   wherein the source electrode is in contact with a side surface of the third oxide layer, and   wherein the drain electrode is in contact with a side surface of the third oxide layer.   
     
     
         4 . The semiconductor device according to  claim 2 , wherein the second oxide layer comprises zinc. 
     
     
         5 . The semiconductor device according to  claim 2 , wherein each of the first oxide layer and the third oxide layer comprises indium and zinc. 
     
     
         6 . The semiconductor device according to  claim 2 ,
 wherein the second oxide layer comprises zinc, and   wherein each of the first oxide layer and the third oxide layer comprises indium and zinc.   
     
     
         7 . The semiconductor device according to  claim 2 , wherein the second oxide layer comprises a crystal. 
     
     
         8 . The semiconductor device according to  claim 7 , wherein the second oxide layer is a non-single-crystal semiconductor layer. 
     
     
         9 . A semiconductor device comprising:
 an oxide stacked layer comprising a first oxide layer, a second oxide layer over the first oxide layer, and a third oxide layer over the second oxide layer;   a source electrode over the oxide stacked layer, the source electrode being in contact with a side surface of the oxide stacked layer; and   a drain electrode over the oxide stacked layer, the drain electrode being in contact with a side surface of the oxide stacked layer,   wherein energy at a bottom of a conduction band of the second oxide layer is lower than energy at a bottom of a conduction band of the first oxide layer and energy at a bottom of a conduction band of the third oxide layer,   wherein the second oxide layer comprises indium, and   wherein each of the first oxide layer and the third oxide layer comprises gallium.   
     
     
         10 . The semiconductor device according to  claim 9 , wherein the second oxide layer comprises zinc. 
     
     
         11 . The semiconductor device according to  claim 9 , wherein each of the first oxide layer and the third oxide layer comprises indium and zinc. 
     
     
         12 . The semiconductor device according to  claim 9 ,
 wherein the second oxide layer comprises zinc, and   wherein each of the first oxide layer and the third oxide layer comprises indium and zinc.   
     
     
         13 . The semiconductor device according to  claim 9 , wherein the second oxide layer comprises a crystal. 
     
     
         14 . The semiconductor device according to  claim 13 , wherein the second oxide layer is a non-single-crystal semiconductor layer.