Low-Stress W/Cr Films for SCALPEL(R) Mask Scattering Layers

I describe the development of low-stress W/Cr bilayer films for use as SCALPEL(R) mask scattering layers. These films are produced by DC magnetron sputtering in argon, and consist of 25 to 50-nm-thick W layers deposited onto 5 to 10-nm-thick Cr layers. X-ray reflectance analysis is used to measure the thicknesses of the individual W and Cr layers with sub-angstrom precision, surface and interface roughnesses, film densities, and also the thickness of the tungsten- oxide overlayer which forms after exposure to air are determined by this technique as well. Film stress, which is measured using the water curvature technique, is controlled by adjusting the deposition conditions such that the Cr layers are in tension while the W layers are in compression (and thus have high density and low surface roughness), so that the net stress in the bilayer is balanced near zero.