PURPOSE: A method for forming a pattern structure is provided to prevent defect to a semiconductor device by protecting a lower layer through a sacrificial layer in a mask processing mask. CONSTITUTION: A mask(104) is formed on an etched layer which is formed on a lower layer. Patterns(106) are formed on the lower layer by etching a target layer using a mask. A sacrificial layer(110) is filled between the patterns and the mask and is formed to cover the lower layer. The mask is removed. The sacrificial layer is partially etched between the patterns when the mask is removed. The remaining sacrificial layer is removed from the lower layer through ashing or strip.
