Membrane Masks for X-ray Lithography: A Search for New Materials.

We have examined polycrystalline Si and amorphous silicon nitride films as potential candidates for thin membranes suitable for x-ray lithography masks. Our initial effort has concentrated on two main aspects of membrane formation: 1) dependence of stress in the films on deposition conditions, and 2) finding conditions for wet etching of the substrates that results in large, defect-free membranes stretched over support rings. Films of polycrystalline Si and of amorphous silicon nitride, 0.6 to 2microns thick, have been deposited on Si, oxidized Si and fused silica wafers under a variety of conditions, followed by removal of the thick substrate by etching. The data indicate that Si sub 3 N sub 4 deposited in plasma at 800C by CVD is highly tensile (~1 x 10 sup (10) dyn cm sup (-2)), whereas it is compressive when deposited in plasma at 300C.