OPC-free on-grid fine random hole pattern formation utilizing double resist patterning with double RETs

摘要

A novel process of OPC-free on-grid fine random hole pattern formation is developed. Any random hole pattern with ～120nm diameter on 240 nm base grid can be printed by KrF exposure. In this technique, double resist patterning scheme is adopted. Dense hole pattern is delineated with first resist process. Quadrupole illumination is applied with embedded attenuating phase shift mask (EA-PSM) in imaging on this step. As is well known, fine dense hole pattern is formed with very large process latitude. After development of the first resist, hardening of the resist film by Ar ion implantation is carried out so as not to mix with second resist at second coating. This hardening process is very robust such that rework in second resist process can be performed with stripping the resist by a solvent. Then, second resist patterning is carried out. In the second exposure, cross-pole illumination is applied with high transmission EA-PSM. By this imaging, very fine dark spot image is generated. Resultantly, fine random pillar patterns, which plug an underlying hole, are formed in the second resist film. Because function of the pillar is plugging a hole, no precise CD control is required. Moreover, pattern connection between adjacent pillars does not cause any problem. Hence, no OPC is needed in the pillar formation, regardless of printed size variation of the pillars. Undesired holes in the dense holes are plugged by the pillars. As a result of the double resist patterning, on-grid random hole pattern is successfully delineated. Due to the robustness of each patterning process, very high process latitude is achieved. Off course, this technique can be carried out under any wavelength on regard of imaging. In other aspect, this technique utilizes only positive-tone resist. Hence, this technique can be applied with leading-edge ArF immersion lithography. As a conclusion, this technique is a promising candidate of hole pattern formation in 32nm era and beyond.