Enhancement of film-forming reactions for microcrystalline Si growth in atmospheric-pressure plasma using porous carbon electrode Available to Purchase

We have investigated the structural and electrical properties of microcrystalline silicon $(μc-Si:H)$ films deposited with high rates $(≥5nm/s)$ at $220°C$ in atmospheric-pressure $He/H2/SiH4$ plasma excited by a 150 MHz, very high-frequency (VHF) power. For this purpose, Si films are prepared varying the deposition parameters, such as $H2$ and $SiH4$ flow rates (⁠$H2$ and $SiH4$ concentrations) and VHF power density, using two types of electrode (porous carbon and cylindrical rotary electrodes). In the case of using the porous carbon electrode, a $μc-Si:H$ film having a crystalline volume fraction of 71.9% is obtained even when hydrogen is not added to the process gas mixture $(H2/SiH4=0)$⁠. In addition, the films exhibit considerably low defect densities of $(3–5)×1016cm–3$ despite the high deposition rates. Such high-rate depositions of good-quality films are realized primarily due to the chemical and physical excitations of the film-growing surface by the atmospheric-pressure plasma while suppressing ion damage and excessive heating of the surface. On the other hand, when using the cylindrical rotary electrode, the phase transition from amorphous to microcrystalline occurs at around $H2/SiH4=70$⁠. The enhancement of the film-forming reactions by the porous carbon electrode are discussed from the viewpoint of the gas residence time in the plasma.