In this study, a precursor gas mixture of toluene and Ar was used for the deposition of a-C:H films on a trench (20-mm pitch and 10-mm depth), and the effect of the Ar flow ratio on the film properties was investigated. The a-C: H films were deposited using a bipolar-type plasma based ion implantation and deposition technique under a negative pulse voltage of -2 kV. The mechanical properties of the prepared a-C: H films, including internal stress, hardness and adhesion strength, were measured by means of surface profilometry, nanoindentation and a microscratch test, respectively. Furthermore, the microstructure of a-C: H films was evaluated by Raman spectroscopy and Fourier transform infrared spectroscopy ( FTIR). The results showed that the thickness uniformity across the trench surface is improved by the addition of Ar, in particular, at an Ar flow ratio of 80%. The film on the top and bottom surfaces of the trench tends to change from a PLC to DLC structure with increasing Ar flow ratio, resulting in a significant improvement of mechanical properties. In the case of the sidewall, the film tends to change to a more GLC structure with increasing Ar flow ratio due to the Ar+ ion bombardment and sputtering effect. (C) 2017 Elsevier B.V. All rights reserved.