For 157 nm lithography the pellicle material will be most probably a 800 μm thick inorganic (fluorine doped fused silica) plate instead of a standard thin (~ 1 μm) organic (polymer) film. The thickness of the pellicle makes it an additional optical element in the 157 nm exposure tool. This puts tight requirements on the optical properties of the pellicle. One of the largest challenges is to control the pellicle induced overlay errors that result from small variations in pellicle flatness. A local tilt of 12 μrad already introduces an image displacement of 1 nm. This paper deals with the theoretical understanding of the pellicle indued overlay errors. It shows the relation between offline pellicle flatness measurements and exposure tool overlay performance. Two potential solutions are presented to obtain the pellicle within the desired overlay specification. System overlay corrections in combination with a new mounting strategy based on 'correctable pellicle shapes' seem to make the desired overlay specification (≤ 1 nm) feasible. The proposed 'one-dimensional' pellicle shape seems to be very promising. Distortion data, as obtained from exposures on a 193 nm system with and without pellicle, indicate that the proposed solution for automatically and fully correcting for a non-flat pellicle is feasible.

Date Published: 2 June 2004
PDF: 11 pages
Proc. SPIE 5504, 20th European Conference on Mask Technology for Integrated Circuits and Microcomponents, (2 June 2004); doi: 10.1117/12.568003

Published in SPIE Proceedings Vol. 5504:
20th European Conference on Mask Technology for Integrated Circuits and Microcomponents
Uwe F. W. Behringer, Editor(s)