Application of Infrared Reflection–Absorption Spectroscopy for Characterizing Vapor-Phase Infiltration (VPI) Processes

Infrared reflection–absorption spectroscopy (IRRAS) is an optical technique used to study ultrathin and even sub-monolayer of molecules absorbed on IR-reflective substrates such as metals. Experimentally, it involves measuring the change in the reflectance-absorption spectra of the substrate with respect to incident angle and/or polarization of an IR probe. The method has been widely adopted for the in-situ monitoring of surface chemical reaction in the catalysis research field. In this talk, I will present the application of IRRAS on understanding the process and material characteristics of vapor-phase infiltration (VPI), an organic-inorganic hybridization method derived from atomic layer deposition (ALD). The examples to be discussed include inorganic infiltration into photoresists such as ZnO into SU-8, an epoxy-based negative-tone photoresist, and Hf organometallic precursor into poly(methyl methacrylate) (PMMA), a well-known positive-tone electron-beam resist. Though the given examples represent ex-situ studies, IRRAS has potential for in-situ interrogation of vapor-phase thin-film processes.