A comparison of multi-level and single-level resist processes and their impact on stepper lens resolution.

Major improvements have been obtained in the planarizing base layer of a trilevel process by the use of an in-line, ramped, hard-bake process. This bake process rapidly passivates the base layer and increases its absorption at the exposure wavelength while maintaining a transmission suitable for alignment purposes. A comparison of GCA and Nikon stepper lenses using Hunt HPR- 204 and Shipley S-1400 as the patterning resist shows that by choosing a high resolution, high contrast resist system, improvements in stepper lens resolution can be achieved without costly lens retrofits. The trilevel resist process described here has improved resolution by at least 0.1micron and a depth of focus (DOF) improvement of >1micron compared to a single level resist process. The trilevel resist process exhibits minimal standing wave effects, improved resist profile, and increased process latitude.