22 nm node contact hole formation in extreme ultra-violet lithography

Patterning of contact hole is always the most difficult process among many types of pattern formations. Specially for the Extreme Ultra-Violet Lithography (EUVL), it will be even more difficult to make perfectly circled contact hole due to the shadow effect. The shape of contact hole will be elliptical because the vertical axis opening is different from the horizontal axis opening. We studied this behavior for 22 nm node contact hole patterns. We varied the pitch of the regular contact hole array. The dependency of the position and density is studied for the random array. In addition to that the thickness of the absorber and the reflectivity of the multilayer are varied to see non-circular contact hole. In order to make desired circular contact hole with uniform width, direction dependent mask bias is applied in addition to the normal optical proximity correction