THE INFLUENCE OF SLOPED ABSORBER SIDEWALLS IN DEEP X-RAY-LITHOGRAPHY

An unfavourable transition region exists in deep x-ray lithography bet ween the exposed and unexposed resist both when the absorbers on the m ask are inclined as well as when the mask and substrate are tilted wit h respect to the x-ray beam. The slope of the resist walls is calculat ed according to an idealized assumption to exceed the slope of the abs orber by a factor of more than 200. In experiments, however, a value o f approximately 40 has been found. This lower value can be explained b y the characteristics of the developer. For a very large transition re gion such as obtained by a tilt of some ten degrees, unoptimized devel opment conditions lead to debris in deep and narrow trenches. When cle an development occurs, the sidewall quality is the same as when there is a step increase in absorber height. Optically patterned resist temp lates may therefore be used for x-ray masks. In addition, tilting the mask and substrate offers a way to obtain three dimensional resist str uctures.