SiN films for x‐ray mask membranes were prepared using a low pressure chemical vapor deposition system designed for high temperature deposition and low impurity incorporation. The physical and optical properties of the films such as stress, uniformity, optical transmittance, and absorption were investigated. Film composition and impurities were also evaluated. The SiN film deposited at a substrate temperature of 1000 °C showed suitable properties for x‐ray mask membrane, such as well controlled tensile stress of about 5×107Pa, high optical transmittance over 95% at 500 to 800 nm, and low impurity concentration.