US Patent 10157775 Method for manufacturing a semiconductor device

In a pattern forming method, a stacked structure, including a bottom layer, a middle layer and a first mask layer, is formed. The middle layer includes a first cap layer, an intermediate layer and a second cap layer. The first mask layer is patterned by using a first resist pattern as an etching mask. The second cap layer is patterned by using the patterned first mask layer as an etching mask. A second mask layer is formed over the patterned second cap layer, and is patterned by using a second resist pattern as an etching mask. The second cap layer is patterned by using the patterned second mask layer as an etching mask. The intermediate layer and the first cap layer are patterned by using the patterned second cap layer as an etching mask. The bottom layer is patterned by using the patterned first cap layer as an etching mask.