We have investigated the structural and electrical properties of microcrystalline silicon (μc-Si:H) films deposited with high rates (≥5 nm/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)×1016 cm–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.

This work deals with the structural properties of microcrystalline silicon (μc-Si:H) films grown at low temperatures (90–220 °C) with high rates in atmospheric-pressure He/H2/SiH4 plasma, which is excited by a 150 MHz very high frequency power using a porous carbon electrode. This plasma permits to enhance the chemical reactions both in gas phase and on the film-growing surface, while suppressing ion impingement upon the surface. Raman crystalline volume fractions of the μc-Si:H films are studied in detail as functions of film thickness and substrate temperature (Tsub). The results show that the μc-Si:H film deposited with 50 (SCCM) (SCCM denotes standard cubic centimeters per minute at STP) SiH4 has no amorphous transition layers at the film/substrate interface in spite of the high deposition rate of 6.4 nm/s, which is verified by the cross sectional observations with a transmission electron microscope. In addition, the Tsub dependence of Raman crystallinity of the μc-Si:H films indicates that a highly crystallized μc-Si:H film grows even when Tsub is reduced to 90 °C. Further systematic studies are needed for both device applications and deposition on thermally sensitive plastic materials.

Low‐temperature and high‐rate depositions of hydrogenated microcrystalline silicon (μc ‐Si:H) films are investigated using stable plasma excited at atmospheric pressure (AP) by supplying 150‐MHz very high‐frequency (VHF) power. VHF power density, H2/SiH4 ratio and plasma gap are varied as parameters under a fixed substrate temperature (Tsub) of 220 ΩC. Increasing VHF power density and H2/SiH4 ratio is primarily important for the sufficient decomposition of source gas molecules, improving both deposition rate and film property. In addition, the plasma gap is found to be another crucial parameter in the deposition process using AP‐VHF plasma. Numerical analyses on the temperature distribution around the plasma region have revealed that the steady‐state surface temperature of the glass substrate becomes approximately 100 ΩC higher than the back surface temperature (Tsub), which is caused by the moderate surface heating effect of the AP‐VHF plasma. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract