Provided is a patterning method including following steps. A doped polysilicon layer, a core layer, and an undoped polysilicon layer are sequentially formed on a target layer. The undoped polysilicon layer is patterned to form a polysilicon pattern. A first etching process is performed by using the polysilicon pattern as a mask to remove a portion of the core layer to form a core pattern. A second etching process is performed to remove the polysilicon pattern. An atomic layer deposition (ALD) process is performed to form a spacer material on the core pattern and the doped polysilicon layer. A portion of the spacer material is removed to form a spacer on a sidewall of the core pattern. A portion of the core pattern and an underlying doped polysilicon are removed.