Deposition of a-C:H films on inner surface of high-aspect-ratio microchannel

• Published in: Journal of applied physics 2016-08, Vol.120 (6)
• Main Authors: Hirata, Yuki, Choi, Junho
• Format: Article
• Language: English
• Subjects: Amorphization; Coating; Collision dynamics; Computer simulation; Deposition; Direct simulation Monte Carlo method; Film thickness; Hardness; High aspect ratio; Ion implantation; Microchannels; Nanoindentation; Particle in cell technique; Plates (structural members); Radicals; Raman spectroscopy
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4960694

Hydrogenated amorphous carbon (a-C:H) films were prepared on inner surface of 100-μm-width microchannel by using a bipolar-type plasma based ion implantation and deposition. The microchannel was fabricated using a silicon plate, and two kinds of microchannels were prepared, namely, with a bottom layer (open at one end) and without a bottom layer (open at both ends). The distribution of thickness and hardness of films was evaluated by SEM and nanoindentation measurements, respectively, and the microstructures of films were evaluated by Raman spectroscopy. Furthermore, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision and Direct Simulation Monte Carlo to investigate the coating mechanism for the microchannel. It was found that the film thickness decreased as the depth of the coating position increased in the microchannels where it is open at one end. The uniformity of the film thickness improved by increasing the negative pulse voltage because ions can arrive at the deeper part of the microchannel. In addition, the hardness increased as the depth of the coating position increased. This is because the radicals do not arrive at the deeper part of the microchannel, and the incident proportion of ions relative to that of radicals increases, resulting in a high hardness due to the amorphization of the film. The opening area of the microchannel where the aspect ratio is very small, radicals dominate the incident flux, whereas ions prevail over radicals above an aspect ratio of about 7.5. On the other hand, in the microchannels that are open at both ends, there were great improvements in uniformity of the film thickness, hardness, and the film structure. The a-C:H films were successfully deposited on the entire inner surface of a microchannel with an aspect ratio of 20.