Development of Low Temperature Deposition Process of Carbon Thin Film by Low Frequency 50Hz Plasma CVD.

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Hydrogenated amorphous carbon (a-C : H) films show large thermal conductivity, chemical inertness, high electrical resistivity and breakdown field, and optical transparency, all of which are suitable for the coating material in microelectronics as well as in mechanical applications. A number of reports have been published on the preparation of a-C : H films by various methods. The low-temperature formation of such an a-C : H film is required for microelectronics application. The purpose of the present study is to deposited of amorphous carbon films on unheated substrate using low frequency 50Hz plasma CVD with hydrogen and methane (H_2+CH_4) mixtures. The results obtained may be summarized as below.1) Major electrical and optical properties of the present a-C : H films were measured. The films were highly transparent and showed very uniform interference color. The refractive index, resistivity, breakdown field strength and the optical band gap of the obtained a-C : H film were 2.4, 10^ … More <14> OMEGA cm, 10^6 V/cm and 4.0 eV, respectively. The deposition rate of a-C : H films under the condition specified above was 60 A/h.2) Infrared absorption as well as Raman spectroscopy showed that the film predominantly consisted of sp^3-bonded C.3) The electron temperature for H_2+CH_4 plasma at 50Hz to 13.56MHz plasma power frequency range was measured from the two-line radiance ratio method using the Balmer lines (Halpha, Hbeta). The electron temperature slowly decreased with increased plasma frequency below 200 kHz, but rapidly decreased between 200 kHz and 13.56MHz. The electron temperature was 16000 K at 1kHz and 8200 K at 13.56 MHz. Accordingly, it was deduced that the electron temperature of low-frequency plasmas is larger than that in high-frequency plasmas.4) From these results, it appears that dissociation of H_2+CH_4 gas is accelerated by high temperature electrons in 50Hz plasma. Moreover, the positive ion in 50Hz plasmas bombard on the deposited film, and the bombarding ion energy is spent as migration energy for rearrangement of deposited atoms. Therefore, the deposited a-C : H films by the 50Hz plasma CVD have the high-quality properties without substrate heating. Less