TUNGSTEN ABSORBER ON SILICON MEMBRANE

A method for manufacturing low-stress tungsten (W) films-as the absorb ers of X-ray masks has been developed. W films with a thickness of 800 nm were deposited by the low pressure chemical vapor deposition (LPCV D) technique, The deposited films consist of the stable alpha-W phase with a Si content of < 4 at%. The density of the films is 18 +/- 0.5 g /cm(3), which is dense enough to yield a sufficient mask contrast (gre ater than or equal to 10) for X-ray exposures. To improve the mechanic al situation, the films were implanted with 66 keV N+ ions at room tem perature. With an optimum dose of (2-8) x 10(15) ions/cm(2), the stres ses in the films were found to be reduced from 10(9)-10(10) to less th an 7 x 10(7) dyn/cm(2). No detectable changes in microstructure were o bserved after implantation, except the lattice parameter of the implan ted top layer of the films was increased from 3.156 to 3.176 Angstrom, which resulted in volume expansion of the top layer with compressive stresses that could compensate the unimplanted lower layer with initia lly tensile stresses and led to stress reduction.