1. Field of the Invention
The present invention relates to a transmission electron diffraction measurement apparatus and a method for measuring a transmission electron diffraction pattern. In particular, the present invention relates to a method for measuring change in a transmission electron diffraction pattern of a substance.
2. Description of the Related Art
In recent years, an oxide semiconductor film has attracted attention. For example, a transistor which includes an amorphous In—Ga—Zn oxide film is disclosed (see Patent Document 1). An oxide semiconductor film can be formed by a sputtering method or the like, and thus can be used for a semiconductor film of a transistor in a large display device. Moreover, a transistor including an oxide semiconductor film has a high field-effect mobility; therefore, a high-performance display device where driver circuits are formed over the same substrate can be obtained. In addition, there is an advantage that capital investment can be reduced because part of production equipment for a transistor including an amorphous silicon film can be retrofitted and utilized.
Synthesis of a single crystal In—Ga—Zn oxide is reported in 1985 (see Non-Patent Document 1). Furthermore, it is reported that an In—Ga—Zn oxide has a homologous structure and is represented by a composition formula, InGaO3(ZnO)m (m is a natural number) (see Non-Patent Document 2).
A transistor which includes a crystalline In—Ga—Zn oxide film and has excellent electrical characteristics and reliability as compared to a transistor including an amorphous In—Ga—Zn oxide film is reported (see Non-Patent Document 3). Non-Patent Document 3 reports that a clear crystal grain boundary is not observed in an In—Ga—Zn oxide film including a c-axis aligned crystal (CAAC).
It is known that a crystal grain boundary in a semiconductor film adversely affects the electrical characteristics of a. transistor. There is a possibility that a crystal structure in which a crystal grain boundary is not clearly observed, such as an In—Ga—Zn oxide film including CAAC, is a novel crystal structure.