Semiconductor device and manufacturing method thereof

摘要

A semiconductor device having favorable electric characteristics and a manufacturing method thereof are provided. A transistor includes an oxide semiconductor layer formed over an insulating layer, a source electrode layer and a drain electrode layer which overlap with part of the oxide semiconductor layer, a gate insulating layer in contact with part of the oxide semiconductor layer, and a gate electrode layer over the gate insulating layer. In the transistor, a buffer layer having n-type conductivity is formed between the source electrode layer and the oxide semiconductor layer and between the drain electrode layer and the oxide semiconductor layer. Thus, parasitic resistance is reduced, resulting in improvement of on-state characteristics of the transistor.

主权项

1. A method for manufacturing a semiconductor device, comprising the steps of:
forming an insulating layer over a substrate having an insulating surface; forming an island-shaped oxide semiconductor layer over the insulating layer; forming a buffer layer having n-type conductivity over the island-shaped oxide semiconductor layer; forming a metal layer over the buffer layer; selectively etching the buffer layer and the metal layer to form a source region and a drain region over the island-shaped oxide semiconductor layer; forming a gate insulating layer over the source region, the drain region, and the island-shaped oxide semiconductor layer; and forming a gate electrode layer over the gate insulating layer to overlap with the island-shaped oxide semiconductor layer, wherein the gate insulating layer is in contact with the island-shaped oxide semiconductor layer.