In recent years, a technique of forming a thin film transistor (TFT) using a semiconductor thin film (with a thickness of approximately from several nm to several hundreds nm), which is formed over a substrate having an insulated surface (with a thickness of several hundreds nm or more and a large area), has been attracted. The thin film transistor has been widely applied in various electronic devices such as an IC and an electronic apparatus and, particularly, development related to a thin film transistor having a polysilicon TFT has been conducted and applied to an active matrix type liquid crystal display device in these days. In addition, recent years have seen the development of a technique of forming a thin film transistor using an oxide semiconductor, instead of the thin film transistor using amorphous silicon. The techniques are for forming a TFT using a crystalline silicon film formed over an insulating surface; in the case where the silicon film is used, however, the number of manufacturing steps is increased and also the number of masks used for forming such a TFT is increased. Moreover, in the case of the TFT using the amorphous silicon film, it is difficult to obtain a TFT having a good field effect mobility, since the film quality of the amorphous silicon film is bad. Therefore, it is difficult to obtain a high speed operation of the TFT. Therefore, in order to resolve such a problem, it has been proposed to use an oxide semiconductor for forming a channel formation region of a TFT (for example, see Patent Document 1). In the case where an oxide semiconductor is used to form a channel formation region, an insulating film is provided between a source region or a drain region of the TFT and the channel formation region; thus, by separately using materials for the insulating film and the channel formation region, a problem of leakage current between the channel formation region and the source region or the drain region can be reduced. Moreover, since an oxide semiconductor has higher mobility than amorphous silicon, a driver circuit with high-speed operation can also be formed using the TFT. Further, it has been confirmed that an oxide semiconductor has an excellent band gap in comparison with a crystalline silicon and, therefore, the electric properties of the TFT can be significantly improved to enable a high electric field to be applied. Examples of the oxide semiconductor include, in addition to zinc oxide, the oxide semiconductors In2O3, SnO2, In—Ga—Zn—O, and the like. The examples provide the property of a semiconductor similarly to amorphous silicon, while providing an advantage of higher mobility than amorphous silicon. Therefore, it is expected to be used for applications and developments of a driver circuit, a memory device and the like which are formed over a substrate over which a circuit is formed. It is noted that the aforementioned oxide semiconductor has a disadvantage of high production costs since an expensive vacuum deposition apparatus is used for a sputtering method in the case of forming a TFT using the oxide semiconductor. Therefore, there has been considered a method in which a thin film transistor is formed using an oxide semiconductor over a substrate with the use of a sputtering method, so that the oxide semiconductor formed over the substrate is crystallized to improve an electric property. Herein, examples of the crystal growth includes a technique in which an amorphous silicon film is crystallized by laser irradiation or a technique in which an amorphous silicon film is crystallized using heat treatment. However, since an amorphous silicon film which is formed over the insulating surface is an amorphous material, it is difficult to keep a shape after the laser irradiation or heat treatment of the amorphous silicon film. In the case of laser irradiation, it is necessary to scan an irradiated surface with the laser all the time to make a beam spot uniform. However, it is difficult to keep uniformity in the entire surface of the substrate. In the case where the heat treatment is carried out, although an insulating surface is used, it is difficult to control the surface temperature of the insulating surface, since the heat conduction through an oxide insulating film and the like is bad. In addition, in the case where the insulating surface is deformed, it is difficult to make an optical path uniform. Accordingly, since the light transmittance is lowered, a region which has been irradiated with the laser may not be crystallized; or, a region which has not been irradiated with the laser may be crystallized. In such a case, there is a problem in that the reliability is impaired. In contrast to such a problem, Patent Document 2 discloses that crystals are easily grown along a substrate by providing concaves and convexes on an insulating surface. Moreover, Patent Document 3 discloses that a heat treatment temperature can be made low (400° C. or lower) when oxide is used. It is described that, in the case where the substrate is made of quartz, heat treatment is carried out at a high temperature. In the case where the substrate is made of glass, heat treatment is carried out at a low temperature (600° C.). Furthermore, Patent Document 4 discloses that, as means of applying a high temperature when crystallization is conducted in an oxidizing atmosphere, a laser irradiation can be used. In addition, it is described that the laser irradiation for crystallization is preferably conducted in an oxidizing atmosphere since crystallization in a non-oxidizing atmosphere has been reported to cause deterioration in TFT characteristics and increase in the threshold voltage in the case of crystallization by laser irradiation. Patent Document 1: Japanese Patent Laid-Open No. 2003-297934 Patent Document 2: Japanese Patent Laid-Open No. 2006-049361 Patent Document 3: Japanese Patent Laid-Open No. 2006-049362 Patent Document 4: Japanese Patent Laid-Open No. 2002-359250 Non-Patent Document 1: F. Ebisawa et al., Journal of Applied Physics, Vol. 105, p. 1021101, 2009