Effect of CH4partial pressure on the microstructure and mechanical properties of magnetron sputtered TiC films

Abstract

TiC thin film has become one of the most frequently used hard coatings because of its high hardness (26– 31 GPa), good wear resistance, low coefficient of friction against steel, and other excellent properties [1]. It can be deposited by chemical or physical vapor deposition (CVD or PVD). TiC films manufactured by PVD have the advantages of low deposition temperature, high quality, and high deposition speed, etc. [2]. Reactively sputtered TiC films are deposited by using gases which contain carbon such as CH4 and C2H2. Compared with using highly active C2H2, the processing is better controlled by using CH4. In this paper, TiC thin films were deposited with reactive magnetron sputtering method at different CH4 partial pressures and the effect of CH4 on their phase, microstructure, and mechanical properties was investigated. TiC films were deposited on silicon substrates by using radio frequency (RF) magnetron sputtering at room temperature. The substrates were ultrasonically cleaned in acetone and alcohol and then mounted on the substrate holder in the vacuum chamber. To improve the adhesion, a metallic Ti layer with a thickness of approximate 200 nm was deposited prior to the deposition of the ceramic TiC films. The TiC films were deposited from a pure Ti target (99.99%) in an Ar and CH4 mixture atmosphere. The Ar partial pressure was kept at 0.3 Pa, while the CH4 partial pressure varied from 0.01 to 0.08 Pa. (The CH4 partial pressure was 0.01, 0.02, 0.04, 0.06 and 0.08 Pa; specimens were numbered from 1 to 5 respectively). During this study, the target power was kept at 200 W and the deposition time was 120 min for each specimen. The phase formation and microstructure of films were investigated by X-ray diffraction (XRD) using a Dmax-rC diffractor and transmission electron microscopy (TEM) using a JEM-100CX TEM. The morphology of films was observed using a Nanoscope IIIa atomic force microscope (AFM). Mechanical property measurements of TiC thin films were carried out using a Fischerscope HV100 microhardness tester and the results were checked by AFM. The XRD spectra of the TiC films deposited at different CH4 partial pressures are shown in Fig. 1. It can be seen that at the CH4 partial pressure of 0.01 Pa, the film mainly contains metallic Ti. When CH4 pressure increases from 0.02 to 0.04 Pa, the films are single phase fcc TiC. When the CH4 partial pressure is higher than