In a semiconductor device manufacturing process, an etching process is performed to various semiconductor layers. As one of such semiconductor layers, a polycrystalline silicon layer may be used. When a polycrystalline silicon layer as an etching target layer is etched, generally, a mask made of silicon oxide is formed on the etching target layer, and an etching process is performed to the etching target layer with the mask. Such an etching method is described in, for example, Patent Document 1.
To be more specific, in the etching method described in Patent Document 1, a silicon oxide layer is formed on the etching target layer which is a polycrystalline silicon layer, and a resist mask is formed on the silicon oxide layer. Then, the silicon oxide layer is etched using the resist mask, and, thus, a mask made of silicon oxide is formed. Then, the resist mask is removed. Thereafter, the etching target layer is etched with plasma of an etchant gas with the mask made of silicon oxide.