Substrate processing device, substrate processing method, and storage medium

An object of the invention is to improve the surface roughness of a mask pattern and to suppress variation in the general shape of the mask pattern. A device is configured so as to comprise a mounting stage 24, which is provided inside a processing chamber 21 and has a substrate W disposed thereon with a pattern mask 12 formed on the surface, a pressure reduction mechanism 32 which reduces the pressure inside the processing chamber 21, a light irradiation mechanism 42 which improves the surface roughness of the pattern mask 12 by irradiating vacuum-ultraviolet light onto the substrate W once the pressure inside the processing chamber 21 has been reduced to 1 Pa or less, and a control section 10 which, during the period of time when the pressure inside of the processing chamber 21 is being reduced from 10,000 Pa or higher to 1 Pa, outputs control signals such that the speed of depressurization of the inside of the processing chamber 21 by the pressure reduction mechanism 32 is 50 Pa/second or less.