Patent ID: 6844117

Claim:
A photomask comprising coarse and dense patterns coexisting in a plane which is prepared by performing a series of pattern-forming steps including a step for forming a resist layer on a photomask blank, a step for exposing and patterning said resist layer, a developing step, a step for etching said photomask blank and a step for removing said resist layer, wherein the photomask is characterized in that patterns to be transferred onto a wafer are formed on said photomask blank according to a dry-etching method comprising the steps of dry-etching a metal thin film, using, as an etching gas, a mixed gas including (a) a reactive ion etching gas, which contains an oxygen-containing gas and a halogen-containing gas, and (b) a reducing gas comprising hydrogen chloride added to the gas component (a); wherein the metal thin film is etched such that dense patterns and coarse patterns coexist in a plane, and maximum dimensional differences within the plane are controlled to be within 10 to 50 nm; and wherein said metal thin film is a chromium-containing film, said mixed gas comprises chlorine gas, oxygen gas and hydrogen chloride gas and the relative flow rates of these gases are 70 to 36, 18 to 9 and 13 to 55% by volume, respectively.