PURPOSE: To obtain excellent transmittance and X-ray resistance for visible light, by supporting the outer part of an SiN:F thin film whose content of fluorine atoms is specified with a supporting frame comprising Si.

CONSTITUTION: The outer part of an SiN:F thin film that incorporates fluorine atoms by at least 1% or more is supported with a supporting frame comprising Si, and a substrate is formed. In an X-ray lithography mask substrate comprising the SiN:F thin film, an Si dangling bond is terminated with fluorine ions by adding the fluorine ions into an SiNx film 12. Thus, the amount of hydrogen that is bonded to the Si dangling bond is remarkably decreased. In this way, X-ray resistance is enhanced to a practical level. Transmittance for visible light used in mask position alignment is as high as 80% or more. The X-ray lithography mask characterized by excellent controllability for internal stress, excellent transmittance for soft X rays and excellent surface smoothness is obtained.