PECVD technology deposition of high hardness a-C:H films on micro-drill surfaces: Substrate bias voltage effects

Abstract

The plasma enhanced chemical vapor deposition (PECVD) technique was utilized to produce hydrogenated amorphous carbon (a-C:H) films. The overall structure of the films consists of a Cr/WC transition layer, a WC/a-C:H transition layer, and an a-C:H functional layer. The study investigated the effects of substrate bias voltages (SBVs) of −580 V, −660 V, −740 V, −820 V, and −900 V on the microstructure, mechanical, and tribological properties of a-C:H films. The findings indicate that different SBVs influence the ionic energy during the deposition of a-C:H films, consequently affecting the film growth. In this case, when the SBV is -820 V, C+ with sufficient energy will penetrate beneath the initial layer in the form of shallow injection. Therefore, compared to other experimental groups, the a-C:H films prepared under this condition have the lowest Ra value (0.42 nm), the highest sp3 CC bond content (39.88 %), the maximum hardness (31.6 GPa), the lowest friction coefficient (0.052), and the smallest wear rate (7.48 × 10−8 mm3/(N·m)), demonstrating significantly better mechanical and tribological properties. The a-C:H films, prepared at different SBVs, are deposited on micro-drill surfaces for hole drilling tests. The experimental results indicate that a-C:H films prepared at SBV of −820 V exhibit the satisfactory drilling performance due to the better mechanical and tribological properties. This is evident not only in the minimal surface wear of the film micro-drill after different drilling quantities but also by the satisfactory quality of the corresponding machined holes. The a-C:H film micro-drill prepared at SBV of −820 V exhibited larger process capability index (CPK) values for the machined holes at 500, 1000, and 2000 hole numbers of 5.449, 3.693, and 3.263 respectively. During the 2000th drill on the printed circuit board (PCB) surface, the hole wall roughness (Rz) and nail head values of the machined hole were measured to be 10.6 μm and 1.3, respectively.