Calibrated exposure and focus test patterns for characterization of optical projection printing

Abstract

Special parameter isolating test patterns have been designed, calibrated and tested for monitoring exposure and focus in optical projection printing. The test structures consist of a sequence of square areas filled with process-parameter sensitive pattern types whose dimensions systematically change area to area. For exposure monitoring sub-imageable (period < λ/(NA ∗(1+σ))) features as described by Arden and Widmann were used. For monitoring focus small opague lines and squares with a large period were used. The feature shapes and sizes were selected through two-dimensional aerial image simulation with SPLAT and tested through projection printing in an exposure-focus matrix. The exposure monitor patterns showed good sensitivity and after correcting for bias in mask making were calibrated via a sample algebraic model. The 2D focus targets were considerably more sensitive than 1D targets and both were less sensitive than predicted from aerial image behavior owing to non-vertical resist dissolution phenomena.