Transistor, semiconductor device, and electronic device
摘要
說明書
In the case where an oxide semiconductor layer is formed by a sputtering method, it is preferable that moisture in a deposition chamber in a sputtering apparatus be removed as much as possible. For example, with an adsorption vacuum evacuation pump such as cryopump, the deposition chamber is preferably evacuated to be a high vacuum state (to a degree of about 5×10?7 Pa to 1×10?4 Pa). In particular, the partial pressure of gas molecules corresponding to H2O (gas molecules corresponding to m/z=18) in the deposition chamber in the standby mode of the sputtering apparatus is preferably lower than or equal to 1×10?4 Pa, further preferably lower than or equal to 5×10?5 Pa.
In this embodiment, the case where an oxide semiconductor is used for the semiconductor layer 109 is described.
[Oxide Semiconductor]
An oxide semiconductor of the present invention is described below. An oxide semiconductor preferably contains at least indium or zinc. In particular, indium and zinc are preferably contained. In addition to these, aluminum, gallium, yttrium, tin, or the like is preferably contained. Furthermore, one or more elements selected from boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like may be contained.
Here, the case where an oxide semiconductor contains indium, an element M, and zinc is considered. The element M is aluminum, gallium, yttrium, tin, or the like. Other elements that can be used as the element M include boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium. Note that two or more of the above elements may be used in combination as the element M.
