Use of ion implantation to eliminate stress‐induced distortion in x‐ray masks

One of the most important questions with regard to using x‐ray lithography for integrated circuit manufacturing is whether distortion in the x‐ray mask, caused by intrinsic stress in the absorber material, can be made sufficiently small for all types of patterns. Pattern features should deviate from their assigned in‐plane positions by no more than a fraction of the minimum linewidth. Tungsten (W) is a more desirable absorber than gold because of its thermal stability and its closer match to the thermal expansion coefficient of Si. However, it is difficult to reproducibly deposit W films with zero stress. We describe a compensation technique for eliminating distortion, regardless of the initial absorber stress. Experiments were done on 0.3–0.4‐μm‐thick W patterned on 1‐μm‐thick Si and Si3N4 membranes, suitable for x‐ray masks. Distortions caused by tensile stresses ∼109 dyns/cm2 can be eliminated by Si implantation at doses ∼1016 cm−2. Measurements of deflections at an edge were made using a Linnik interf...