METHOD FOR PRODUCING PHOTOMASK BLANK Russian patent published in 2006 - IPC H01L21/302 

FIELD: electronic engineering; production of photomask blanks.

SUBSTANCE: proposed method for producing photomask blanks includes mechanical and chemical treatment of glass wafers, their placement in vacuum chamber, and coating with masking chromium layer by heating chromium-containing evaporator in nitrogen environment until desired optical density is attained, this being followed by wafer washing, covering with resist, and control. Chromium is cleaned prior to being applied to masking layer by remelting it at temperature of 2000 to 2100°C and residual pressure of 400 - 500 mm of mercury in argon environment; chamber is cooled down to room temperature, evaporator is heated at a rate of 500 - 700°C a minute to 1700 - 1850°C, exposed to this temperature for 25 - 35 minutes, then evaporator is heated to 1860 - 1950°C and chromium is evaporated at a rate of 140 - 160Å a minute until desired optical density is attained.

EFFECT: enhanced quality of varying-reflectance masking layer and environmental friendliness of method.

4 cl, 1 tbl