Semiconductor device and method for manufacturing the same
A transistor including an oxide semiconductor, which has good on-state characteristics, and a high-performance semiconductor device including a transistor capable of high-speed response and high-speed operation. In the transistor including an oxide semiconductor, oxygen-defect-inducing factors are introduced (added) into an oxide semiconductor layer, whereby the resistance of a source and drain regions are selectively reduced. Oxygen-defect-inducing factors are introduced into the oxide semiconductor layer, whereby oxygen defects serving as donors can be effectively formed in the oxide semiconductor layer. The introduced oxygen-defect-inducing factors are one or more selected from titanium, tungsten, and molybdenum, and are introduced by an ion implantation method.
1. A method for manufacturing a semiconductor device comprising:
forming a first oxide semiconductor layer by a sputtering method;
crystallizing a region of the first oxide semiconductor layer by a first heat treatment, the region including a surface of the first oxide semiconductor layer;
forming a second oxide semiconductor layer over the first oxide semiconductor layer by a sputtering method;
crystallizing the second oxide semiconductor layer by a second heat treatment;
wherein the second oxide semiconductor layer includes In, Ga, and Zn, and
wherein the second oxide semiconductor layer includes a crystal whose c-axis is aligned in a direction perpendicular to a surface of the second oxide semiconductor layer.
2. The semiconductor device according to claim 1 ,
wherein the first heat treatment is performed at higher than or equal to 450° C. and lower than or equal to 850° C. for greater than or equal to 1 minute and less than or equal to 24 hours, and
wherein the second heat treatment is performed at higher than or equal to 450° C. and lower than or equal to 850° C. for greater than or equal to 1 minute and less than or equal to 400 hours.
3. A method for manufacturing a semiconductor device comprising:
forming a first oxide semiconductor layer by a sputtering method;
heating the first oxide semiconductor layer;
forming a second oxide semiconductor layer over the first oxide semiconductor layer by a sputtering method;
heating the second oxide semiconductor layer;
wherein the second oxide semiconductor layer includes In, Ga, and Zn, and
wherein the second oxide semiconductor layer includes a crystal whose c-axis is aligned in a direction perpendicular to a surface of the second oxide semiconductor layer.