Semiconductor device and manufacturing method thereof

Abstract

To offer a semiconductor device including a thin film transistor having excellent characteristics and high reliability and a method for manufacturing the semiconductor device without variation. The summary is to include an inverted-staggered (bottom-gate structure) thin film transistor in which an oxide semiconductor film containing In, Ga, and Zn is used for a semiconductor layer and a buffer layer is provided between the semiconductor layer and source and drain electrode layers. An ohmic contact is formed by intentionally providing a buffer layer containing In, Ga, and Zn and having a higher carrier concentration than the semiconductor layer between the semiconductor layer and the source and drain electrode layers.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising:
 a gate electrode;   an oxide semiconductor film over the gate electrode;   an insulating film over and in contact with a channel formation region of the oxide semiconductor film, the insulating film comprising silicon oxide;   a first layer over and in contact with the oxide semiconductor film;   a second layer over and in contact with the oxide semiconductor film;   a source electrode over and in contact with the first layer, the source electrode being electrically connected to the oxide semiconductor film; and   a drain electrode over and in contact with the second layer, the drain electrode being electrically connected to the oxide semiconductor film,   wherein the oxide semiconductor film comprises indium, gallium, and zinc,   wherein the insulating film does not contact the source electrode or the drain electrode,   wherein the source electrode or the drain electrode comprises a first conductive layer and a second conductive layer over the first conductive layer, and   wherein, in a cross sectional view in a channel length direction, the first layer or the second layer comprises a first region which is overlapped by the second conductive layer and a second region which extends beyond an end portion of the second conductive layer in the channel length direction.   
     
     
         3 . The semiconductor device according to  claim 2 , wherein the first layer or the second layer is in contact with a side surface of the oxide semiconductor film. 
     
     
         4 . The semiconductor device according to  claim 2 , wherein a width of the insulating film in the channel length direction is smaller than a width of the gate electrode in the channel length direction. 
     
     
         5 . The semiconductor device according to  claim 2 , wherein an end portion of the first conductive layer extends beyond the end portion of the second conductive layer in the channel length direction. 
     
     
         6 . The semiconductor device according to  claim 2 , wherein the first conductive layer comprises titanium. 
     
     
         7 . The semiconductor device according to  claim 2 , wherein the source electrode or the drain electrode further comprises a third conductive layer over the second conductive layer. 
     
     
         8 . The semiconductor device according to  claim 2 , wherein the first layer or the second layer is a buffer layer including an impurity imparting n-type conductivity. 
     
     
         9 . The semiconductor device according to  claim 2 , wherein the first layer or the second layer comprises an oxide semiconductor comprising indium, gallium, and zinc. 
     
     
         10 . A semiconductor device comprising:
 a gate electrode;   an oxide semiconductor film over the gate electrode;   an insulating film over and in contact with a channel formation region of the oxide semiconductor film, the insulating film comprising silicon oxide;   a first layer over and in contact with the oxide semiconductor film;   a second layer over and in contact with the oxide semiconductor film;   a source electrode over and in contact with the first layer, the source electrode being electrically connected to the oxide semiconductor film; and   a drain electrode over and in contact with the second layer, the drain electrode being electrically connected to the oxide semiconductor film,   wherein the oxide semiconductor film comprises indium, gallium, and zinc,   wherein the oxide semiconductor film comprises a first region overlapped by the source electrode or the drain electrode and a second region in contact with the insulating film,   wherein a thickness of the first region of the oxide semiconductor film is smaller than a thickness of the second region of the oxide semiconductor film,   wherein the insulating film does not contact the source electrode or the drain electrode,   wherein the source electrode or the drain electrode comprises a first conductive layer and a second conductive layer over the first conductive layer, and   wherein, in a cross sectional view in a channel length direction, the first layer or the second layer comprises a first region which is overlapped by the second conductive layer and a second region which extends beyond an end portion of the second conductive layer in the channel length direction.   
     
     
         11 . The semiconductor device according to  claim 10 , wherein the first layer or the second layer is in contact with a side surface of the oxide semiconductor film. 
     
     
         12 . The semiconductor device according to  claim 10 , wherein a width of the insulating film in the channel length direction is smaller than a width of the gate electrode in the channel length direction. 
     
     
         13 . The semiconductor device according to  claim 10 , wherein an end portion of the first conductive layer extends beyond the end portion of the second conductive layer in the channel length direction. 
     
     
         14 . The semiconductor device according to  claim 10 , wherein the first conductive layer comprises titanium. 
     
     
         15 . The semiconductor device according to  claim 10 , wherein the source electrode or the drain electrode further comprises a third conductive layer over the second conductive layer. 
     
     
         16 . The semiconductor device according to  claim 10 , wherein the first layer or the second layer is a buffer layer including an impurity imparting n-type conductivity. 
     
     
         17 . The semiconductor device according to  claim 10 , wherein the first layer or the second layer comprises an oxide semiconductor comprising indium, gallium, and zinc.