Patent ID: 8008211

Claim:
A pattern forming method for forming parallel linear grooves on a substrate by plasma etching, wherein the substrate has thereon three-layer films including from the top a first-layer film, a second-layer film and a third-layer film by using a substrate in which first mask patterns of linear shape are formed on the first-layer film, the method comprising: (a) forming pairs of deposits on both sidewalls of each of mask portions in the first mask patterns by forming a thin film on the first mask patterns, performing an anisotropic etching by plasma to leave downwardly widening deposits at the both sidewalls of each of the mask portions, and exposing a top surface of the second-layer film between the deposits; (b) forming on the second-layer film second mask patterns each formed of a pair of mask portions corresponding to the pair of the deposits by removing the mask portion, plasma etching the second-layer film by using the deposits as a mask, and removing the deposits; and thereafter, (c) forming a thin film on the second mask patterns of the second-layer film, and performing an anisotropic etching by plasma to leave downwardly widening deposits on sidewalls of every two of mask portions facing each other via a region corresponding to a width-directional center of one of the mask portions of the first mask patterns, and to expose a top surface of the third-layer film between the deposits while leaving deposits between adjacent mask portions of two of the second mask patterns; and thereafter, (d) forming grooves on the third-layer film by removing the second mask portion formed on the second-layer film, and etching off the third-layer film by plasma while using the deposits as a mask.