Comparison of exposure, bake, and dissolution characteristics of electron beam and optically exposed chemically amplified resists

Abstract

Fourier-transform infrared (FTIR) spectrometry and dissolution rate measurements are used to compare chemical–physical mechanisms in electron beam and deep-ultraviolet (UV) optical exposure of a chemically amplified negative crosslinking resist, Shipley XP-8843 (SNR-248). In contrast to optical exposure, up to 20% of the maximum extent of reaction by the melamine crosslinking agent, as measured by the change in peak-to-peak absorbance of the infrared (IR) spectrum at 990–1070 cm−1, was observed after electron beam exposure at nominal exposure doses of 0.5–3 μC/cm2. For both electron-beam and optical exposure, the kinetics of the acid-catalyzed crosslinking reactions during the postexposure bake (PEB) were similar and the saturation value of the crosslinking reaction measured by the FTIR was identical. A plot of the dissolution rate versus the degree of crosslinking for normal lithographic doses was single-valued and tended to follow comparable data for optical exposure. When doses >5 μC/cm2 are used without a PEB, the slowing of the dissolution rate is less than expected from IR spectral change. Contrary to typical electron beam exposed negative resists, slightly underexposing small features produced a reentrant profile apparently owing to the high contrast of this resist.