Osamu Takai*, Takenobu Suzuki, Yusuke Taki and Hiroyuki Sugimura

Department of Materials Processing Engineering
Nagoya University, Nagoya 464-8603, Japan
takai@otakai.numse.nagoya-u.ac.jp

Carbon nitride is an interesting carbon material which shows excellent properties. After the calculation by Liu and Cohen, many researchers are trying to prepare b-C3N4 which may be equal to or harder than diamond. Almost carbon nitride films synthesized are amorphous and have N/C ratios less than 0.5. The mechanical, electrical and optical properties of the carbon nitride thin films are, however, interesting in spite of their amorphous structure. This paper reports on the deposition of amorphous carbon nitride thin films by inductively-coupled plasma (ICP)-CVD and the properties of the films.

An ICP-CVD system consists of a stainless steel chamber with a quartz tube around which an inductively-coupled coil is placed, a pumping unit of turbomolecular and rotary pumps, a pressure measuring unit, a gas introducing unit and a substrate holder. A 13.56 MHz generator is used as an rf power source. Acetylene and nitrogen are introduced separately into the chamber from two gas inlets. Amorphous carbon nitride films are deposited onto Si (100) substrates. We keep the gas flow ratio of acetylene to nitrogen constant (1:1) and the rf power constant (1 kW). The total pressure and the dc negative substrate bias voltage are varied.

The N/C ratio in the deposited film decreases with increasing absolute bias voltage at 1 Pa. The ratio is almost constant (0.2) in the range between 0.1 and 10 Pa at -250 V. Application of adequate negative bias voltage on the substrate is effective to increase sp3 domains and film hardness. The film deposited at -250 V is about 1.7 times as hard as the Si substrate which Knoop hardness is about 1400. The structure and chemical bonding state of the films are investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.