Tungsten absorber on silicon membrane

A method for manufacturing low-stress tungsten (W) films as the absorbers of X-ray masks has been developed. W films with a thickness of 800 nm were deposited by the low pressure chemical vapor deposition (LPCVD) technique. The deposited films consist of the stable α-W phase with a Si content of < 4 at%. The density of the films is 18 ± 0.5 g/cm3, which is dense enough to yield a sufficient mask contrast (≥ 10) for X-ray exposures. To improve the mechanical situation, the films were implanted with 66 keV N+ ions at room temperature. With an optimum dose of (2–8) × 1015 ions/cm2, the stresses in the films were found to be reduced from 109–1010 to less than 7 × 107 dyn/cm2. No detectable changes in microstructure were observed after implantation, except the lattice parameter of the implanted top layer of the films was increased from 3.156 to 3.176 Å, which resulted in volume expansion of the top layer with compressive stresses that could compensate the unimplanted lower layer with initially tensile stresses and led to stress reduction.