Aging of Oxygen-Treated Trimethylsilane Plasma-Polymerized Films Using Spectroscopic Ellipsometry

Oxygen-treated trimethylsilane (TMS) plasma-polymerized films are investigated using rotating polarizer and analyzer ellipsometer. Aging process and composition of the samples are studied. Coordinated X-ray photoelectron spectroscopy (XPS) depth profiling studies on these films is presented for more detailed understanding of the aging process as well as the modeling of these films. 1. Introduction Amorphous hydrogenated silicon-carbon thin films have received an increasing interest in the development of optoelectronic devices and in the metallurgical field as a hard protective coating. Low-temperature plasma is one of the many different methods to deposit such films on metals and semiconductors. The interaction between the monomer vapor and the electromagnetic energy can be achieved in different ways. The direct current (DC) approach has proven to be an efficient method in coatings on metals for corrosion protection purposes. The conductive substrate on which the film is being deposited plays the role as the cathode of the DC glow discharge. An enhanced magnetic anode (magnetron) is used to confine and focus the plasma onto the coated substrate. The mechanism of the polymerization can be explained based on the concept of competitive ablation and polymerization [1]. The plasma parameters determine the outcome of the polymerization process to be either etching (ablation) or plasma polymerization. Ellipsometry is a powerful tool for optical characterization of thin films [2–9]. It is used for determining optical properties of materials, thicknesses, porosity, and crystal orientation. The principle of operation of ellipsometry is based on measuring polarization changes occurring upon reflection at oblique incidence of a polarized plane wave [2]. The basic quantities measured with an ellipsometer are the ellipsometric parameters and from which the optical parameters of a structure can be extracted by inverting Fresnel equations [6]. The main interest in this study is to investigate the aging process of oxygen-treated TMS ((CH3)3SiH) plasma-polymerized films using one to two rotating polarizer and analyzer ellipsometer. These kinds of films are very hard to analyze due to the complexity of this problem as well as the wide range of parameters and variables involved. Similar films are believed to be porous, amorphous, macroscopically homogenous, and microscopically heterogeneous. They are composed of silicon, carbon, oxygen, hydrogen, and occasionally nitrogen and fluorine. Therefore, this work is a preliminary trial to understand the aging and composition of