1. Field of the Invention
The present invention relates to a method for manufacturing a silicon on insulator (SOI) substrate in which a crystalline semiconductor layer is provided on an insulating surface and a method for manufacturing a semiconductor device.
Note that the semiconductor device in this specification indicates all the devices that operate by utilizing semiconductor characteristics. For example, electro-optic devices (including liquid crystal display devices and EL display devices), semiconductor circuits, and electronic devices are all included in the category of the semiconductor device.
2. Description of the Related Art
Flat-panel television sets to which thin display devices such as liquid crystal display devices and plasma display devices are applied have been widely used. In recent years, EL television sets to which electroluminescence (hereinafter also referred to as EL) display devices are applied have been developed. One of the main technologies thereof is a thin film transistor. By improving performance of a thin film transistor and reducing manufacturing cost thereof, thin display devices having excellent display performance can be provided inexpensively. In the market of the thin display device (a flat-panel display) where various companies are competing with each other, improvement in performance and cost reduction are essential to gain the ascendancy.
It is necessity that thin film transistors used for a flat-panel display is formed over an inexpensive and large-size substrate such as a glass substrate. In general, thin film transistors using amorphous silicon layers or polycrystalline silicon layers are formed. In terms of performance of a transistor, single crystal silicon is preferable; however, restrictions on a process, particularly restrictions on heat treatment temperature are severe in the case of employing a glass substrate.
On the basis of the above situation, methods for increasing the crystallinity of a semiconductor layer have been researched and developed in order to improve performance of a thin film transistor. As an example, there is a technique where amorphous silicon is irradiated with a laser beam to be polycrystallized. For example, in Patent Document 1, a technique is disclosed in which a high performance thin film transistor having a high quality polycrystal is obtained by scanning a laser beam aligned at an angle of crystal faces of a semiconductor layer.