M. Koide and H. Koinuma*

Ceramics Materials and Structures Laboratory / Tokyo Institute of Technology
4259 Nagatsuta, Midori-ku, Yokohama 226, Japan
koinuma@oxide.rlem.titech.ac.jp

Based on our previous studies on cold plasma torches which can generate homogenous and stable plasma under atmospheric pressure (1,2), we have developed a new plasma generator that enables plasma processings at extremely low gas temperatures and wider processing area. This plasma generator is composed of an rf cathode disk with small holes through which plasma gas blows into the space between the cathode and a grounded anode plate. In the previous plasma torches, it was necessary to place a dielectric tubing or plate right on the anode to stabilize the plasma. In the new system, such a dielectric material was not necessary probably because the native oxide (alumina) layer played the role. By the application of rf(13.56Mhz) voltage to the cathode, homogeneous plasma was generated in an atmospheric pressure He gas flow through the space (50mm,1-2.5mm high) between the both electrodes. Ar plasma could also be generated when He gas flow was gradually exchanged to Ar. The plasma was characterized by optical emission analysis and direct temperature measurement with a thermocouple to reveal the very low gas temperature (Tg) as the most significant feature : Under all the plasma conditions employed, 450-1000 sccm gas flow rates and 15-25W rf power, Tg stayed below 100 C. Mixing a reaction gas in the plasma makes it possible to utilize this plasma for various material processing in open air conditions.

(1) H. Koinuma et al.: Appl. Phys. Lett., 60 (1992) 816
(2) M. Koide et al.: Thin Solid Films, in press