FORMATION OF MONOLITHIC MASKS FOR 0.25-MU-M X-RAY-LITHOGRAPHY

We have constructed monolithic masks for proximity x-ray lithography by forming 1-mu-m thick polycrystalline Si membranes directly on glass support frames. Finished masks are 78 mm in diameter and approximately 5 mm thick, with the Si membrane spanning 27 mm. The monolithic design provides simple processing and unprecedented flatness of 30 nm across the membrane and < 500 nm across the entire disk. Mask blanks were metallized with 500 nm of W that was sputter deposited under conditions that hold the film stress < 50 MPa. Tungsten was patterned by reactive ion etching to form features as small as 0.25-mu-m.