STENCIL MASK TEMPERATURE-MEASUREMENT AND CONTROL DURING ION IRRADIATION

In ion projection lithography a stencil mask consisting of a thin memb rane of silicon is irradiated by a broad, uniform beam of ions. The re sulting image is demagnified and projected on a resist-covered substra te. Energy deposited in the stencil mask by the ion beam can lead to t emperature distributions resulting in nonuniform stress and unacceptab ly large feature displacement. Numerical simulations have shown that t he presence of a cooled cylinder near the mask during irradiation is a n effective means of temperature control. We have experimentally deter mined the temperature distribution in a thin glass disk which is chose n to be thermally equivalent to a Si stencil mask. We have found tempe rature distributions that approximately agree with the numerical compu tations, and have confirmed the effectiveness of a cooled cylinder in reducing the temperature variation over the disk. For example, a graph ite coated (epsilon = 0.85) glass disk, when irradiated by a 3.3 mW/cm (2) ion beam, develops temperature differences of more than 5 degrees C between the center and edge of the disk. Introduction of a cylinder cooled 35 degrees C below room temperature reduces the temperature dif ference to 1.2 degrees C, resulting in thermally induced feature displ acement of less than 10 nm. (C) 1996 American Vacuum Society.