Example methods may provide a thin film etching method. Example thin film etching methods may include forming a Ga—In—Zn—O film on a substrate, forming a mask layer covering a portion of the Ga—In—Zn—O film, and etching the Ga—In—Zn—O film using the mask layer as an etch barrier, wherein an etching gas used in the etching includes chlorine. The etching gas may further include an alkane (CnH2n+2) and H2 gas. The chlorine gas may be, for example, Cl2, BCl3, and/or CCl3, and the alkane gas may be, for example, CH4.