Patent ID: 8686413

Claim:
A semiconductor device comprising: a first conductive layer over a substrate; a first insulating layer over the first conductive layer; an oxide semiconductor layer over the first insulating layer and overlapping with the first conductive layer, the oxide semiconductor layer including a channel region, wherein the first conductive layer is overlapped with the channel region; a second conductive layer in contact with the oxide semiconductor layer; a third conductive layer in contact with the oxide semiconductor layer; a second insulating layer over the oxide semiconductor layer, the second conductive layer and the third conductive layer; and a fourth conductive layer over the second insulating layer and overlapping with the channel region, wherein the oxide semiconductor layer comprises a first region and a second region, wherein the first region is closer to the second insulating layer than the second region, wherein the first region comprises a crystal, and a c-axis of the crystal is substantially perpendicular to the second insulating layer, wherein the second region has a lower crystallinity than the first region, and wherein all the metal elements included in the first region are included in the second region, and all the metal elements included in the second region are included in the first region.