Optical and Mechanical Properties of Toluene-TEOS Hybrid Plasma-Polymer Thin Films Deposited by Using PECVD

Abstract

Toluene-tetraethoxysilane (TEOS) hybrid plasma - polymer thin films were deposited on silicon(100) substrates by using plasma enhanced chemical vapor deposition (PECVD) with a home-made stainless-steel vacuum chamber. Toluene and TEOS were utilized as the organic and the inorganic precursors with hydrogen gas for the toluene bubbler and argon gas for both the TEOS bubbler and the carrier gas. To analyze the thermal, optical, and mechanical properties of the plasma polymerized thin films, we grew hybrid plasma-polymer thin films at various radio-frequency (RF, 13.56 MHz) powers, bubbling ratios of TEOS to toluene precursors, and annealing temperatures. The thin films were analyzed by using ellipsometry and Fourier-transform infrared spectroscopy (FTIR). The refractive indices varied with the RF power, the bubbling ratio of TEOS to toluene, and the annealing temperature. Also, the IR spectra showed that the hybrid plasma-polymer thin films had totally different chemical functionalities from the liquid toluene and the TEOS precursors and that the chemical functionalities of the thin films changed with the RF power, the bubbling gas ratio of TEOS to toluene, and the annealing temperature. The SiO peak intensity increased with increasing TEOS bubbling ratio, and the -OH and the CO peak intensities decreased with increasing annealing temperature. From the field emission scanning electron microscopy (FE-SEM) results, the thickness of the thin films was determined before and after the annealing, with the thickness shrinkage (%) being measured by using SEM cross-sectional images. The MTS nanoindenter xp (R) was used to measure the hardness and Young's modulus and showed that both these values increased as the deposition RF power increased; these values also changed with the bubbling ratio of TEOS to toluene and with the annealing temperature.