1. Field of the Invention
The present invention relates to a semiconductor device having an SOI (silicon on insulator) structure and a manufacturing method thereof. In this specification, a semiconductor device means any device capable of functioning with the use of semiconductor characteristics.
2. Description of the Related Art
In recent years, LSI technology has been drastically progressed, and an SOI structure by which speeding up and low power consumption are realized has been attracted attention. In this technology, an active region (a channel formation region) of a field effect transistor (FET), which has been conventionally formed of a bulk single crystal silicon, is formed of a single crystal silicon thin film. It is known that a MOS field-effect transistor manufactured using an SOI structure has lower parasitic capacitance than that manufactured using a conventional bulk single crystal silicon substrate, which is an advantage in increasing speed.
As a substrate having an SOI structure (hereinafter also referred to as an “SOI substrate”), an SIMOX substrate, a bonded substrate, and the like are known. For example, an SIMOX substrate obtains an SOI structure as follows: oxygen ions are implanted into a single crystal silicon substrate, and heat treatment is performed at 1300° C. or higher to form a buried oxide (BOX) layer, so that a single crystal silicon thin film is formed over a surface of the SIMOX substrate. As for the SIMOX substrate, since oxygen ion implantation can be controlled precisely, a single crystal silicon thin film having a uniform thickness can be formed with good controllability. However, since it is necessary to take a long time for the oxygen ion implantation, there are problems in the time and the cost. Further, there is another problem in that the single crystal silicon thin film gets damaged easily during the oxygen ion implantation.
A bonded substrate obtains an SOI structure as follows: two single crystal silicon substrates (a base substrate and a bond substrate) are bonded to each other with an oxide film interposed therebetween, and one of the two single crystal silicon substrates (the bond substrate) is ground and polished on its rear side (which is not a surface to be bonded) to be thinned, so that a single crystal silicon thin film is formed. It is difficult to form a uniform and thin single crystal silicon thin film by grinding and polishing. Thus, as a thin film technology, Smart-Cut (registered trademark) employing hydrogen ion implantation (e.g., Reference 1: Japanese Published Patent Application No. H5-211128) is also proposed.