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Study of a Two-Stage Photobase Generator for Photolithography in Microelectronics

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journal contribution
posted on 01.03.2013, 00:00 authored by Nicholas J. Turro, Yongjun Li, Steffen Jockusch, Yuji Hagiwara, Masahiro Okazaki, Ryan A. Mesch, David I. Schuster, C. Grant Willson
The investigation of the photochemistry of a two-stage photobase generator (PBG) is described. Absorption of a photon by a latent PBG (1) (first step) produces a PBG (2). Irradiation of 2 in the presence of water produces a base (second step). This two-photon sequence (1 + hν → 2 + hν → base) is an important component in the design of photoresists for pitch division technology, a method that doubles the resolution of projection photolithography for the production of microelectronic chips. In the present system, the excitation of 1 results in a Norrish type II intramolecular hydrogen abstraction to generate a 1,4-biradiacal that undergoes cleavage to form 2 and acetophenone (Φ ∼ 0.04). In the second step, excitation of 2 causes cleavage of the oxime ester (Φ = 0.56) followed by base generation after reaction with water.