Composite oxide semiconductor and method for manufacturing the same

Abstract

The field-effect mobility and reliability of a transistor including an oxide semiconductor film are improved. A semiconductor layer of a transistor is formed using a composite oxide semiconductor in which a first region and a second region are mixed. The first region includes a plurality of first clusters containing one or more of indium, zinc, and oxygen as a main component. The second region includes a plurality of second clusters containing one or more of indium, an element M (M represents Al, Ga, Y, or Sn), zinc, and oxygen. The first region includes a portion in which the plurality of first clusters are connected to each other. The second region includes a portion in which the plurality of second clusters are connected to each other.

What is claimed is: 
     
         1 . A display device comprising:
 a pixel portion and a driver circuit portion, each over a substrate,   wherein the pixel portion includes a first transistor and the driver circuit portion includes a second transistor,   wherein the first transistor includes a composite oxide semiconductor in a channel region,   wherein the composite oxide semiconductor includes a first region and a second region,   wherein each of the first region and the second region includes In, an element M, and Zn,   wherein the element M is at least one of Al, Ga, Y and Sn,   wherein the first region has a higher atomic ratio of In to the element M than the second region,   wherein a portion of the first region is surrounded by the second region, and   wherein a portion of the second region is surrounded by the first region.   
     
     
         2 . A display device comprising:
 a pixel portion and a driver circuit portion, each over a substrate,   wherein the pixel portion includes a first transistor and the driver circuit portion includes a second transistor,   wherein the second transistor includes a composite oxide semiconductor in a channel region,   wherein the composite oxide semiconductor includes a first region and a second region,   wherein each of the first region and the second region includes In, an element M, and Zn,   wherein the element M is at least one of Al, Ga, Y and Sn,   wherein the first region has a higher atomic ratio of In to the element M than the second region,   wherein a portion of the first region is surrounded by the second region, and   wherein a portion of the second region is surrounded by the first region.   
     
     
         3 . A display device comprising:
 a pixel portion and a driver circuit portion, each over a substrate,   wherein the pixel portion includes a first transistor and the driver circuit portion includes a second transistor,   wherein each of the first transistor and the second transistor includes a composite oxide semiconductor in a channel region,   wherein the composite oxide semiconductor includes a first region and a second region,   wherein each of the first region and the second region includes In, an element M, and Zn,   wherein the element M is at least one of Al, Ga, Y and Sn,   wherein the first region has a higher atomic ratio of In to the element M than the second region,   wherein a portion of the first region is surrounded by the second region, and   wherein a portion of the second region is surrounded by the first region.