A new type X-ray mask called Si frame-mounting X-ray mask, by using the bonded SOI (Silicon-On-Insulator) technique has been successfully developed. The combination of bonding a flat 2000 micrometers -thickness Si mask-substrate and a 6 mm-thickness Si plate with 0.5 micrometers -thickness SiO2 film, achieved the local flatness less than 0.3 micrometers in a 25 mm square area and 2.5 micrometers or better for a 3'-diameter mask-substrate. The bonding strength of the interface between a Si mask-substrate and a Si frame was over 0.4 kgf/cm2 and showed sufficiently high chemical proof during a mask fabrication process. The SiCN, as an X-ray transmitting film, deposited by an RF magnetron sputtering system also showed substantially good properties. The amorphous SiCN film had quite smooth surface with Ra of 0.4 nm and high elasticity (E/(1-(upsilon) ) equals 3.2 X 1012 dyn/cm2). Furthermore, the SiCN film coated with an anti-reflective (AR) film made of SiO2 had high transparency of 94% for He-Ne laser beam (633 nm). Consequently, it was verified that this Si frame-mounting X-ray mask by using the bonded SOI technique was excellent in all properties for practical use of an X-ray mask.