| Abstract: | Over the past 20 years a wide variety of materials have been evaluated for use as x-ray mask support membrane. Reference 1 presents a comprehensive list of materials investigated to date. Besides x-ray and optical transparency an important requisite for a mask material is dimensional stability. Since the Young's modulus of elasticity is a measure of the atomic bond strength, the covalently bonded refractory materials such as BN or SiC, and diamond, which have large moduli, are more stable than polymers or metals. BN has been the material of choice for x-ray masks in the United States and Europe for the past 10 years; however, CVD BN contains a significant amount of hydrogen in the as-deposited state and is not sufficiently stable under prolonged x-ray exposure. On the other hand, it has been shown by nuclear reaction analysis that diamond films contain less than 1% hydrogen, despite being synthesized in a predominantly hydrogen gas mixture. The low residual hydrogen content, combined with diamond's other unique characteristics such as high mechanical stiffness and high x-ray transparency, makes it an attractive candidate for an x-ray mask material. |
