High rate diamond deposition using a microwave discharge

Abstract

Washington Universitv -A linear relation between the center depth &d inverse diameter of a contact hole has been derived approximately. This relation was found experimentally for contact holes etched in silicon dioxide and several models for it were computed.1 The new feature here is the application of Langmuir kinetics with synergistic etching of neutrals and the ions. The neutrals are modeled for molecular flow in a pipe with a sticking coefficient equal to one? This is supported by a recent finding that the etching (nondepositive) neutrals are not adsorbed appreciably on top of the same neutrals on the passivated walls of contact holes etched in silicon dioxide3 The ions are modeled simply by a vertical beam since the directed ion energy fluxes at the center of the contact hole fall off slowly with depth. Etch rates for the neutrals and ions are computed from data.1 1. S. C. McNevin, M. Cerullo and J.T.C. Lee, Bull. Am. Phys.Presently, plasma assisted synthesis of diamond films often employs a microwave discharge/reactor for the source of the radical species. Typical deposition takes place using varying CHJM[2/COn gas mixtures over a 20-100 Torr pressure regime and with a CW, 2.45 GHz input power of less than 3 kW. While excellent diamond films are synthesized under these conditions, the linear deposition rates are usually limited to only a few u d h r . Since diamond synthesis costs are still high, it is desirable to deposit high quality diamond films with higher deposition rates.One method to increase the diamond deposition rate is to increase the deposition pressure and discharge absorbed power density. This paper will present the results of an experimental investigation exploring microwave plasma synthesis at the 100-200 Torr pressure and 2.5-6 kW input power regimes. This work, which builds upon earlier reported work [ 1,2], utilizes a microwave reactor developed for operation at higher pressure/ power regimes. Deposition experiments are conducted over wide input experimental regimes, i.e. (1) methane concentration 0% CH&I2 c 15%, (2) pressure: 90-150 Torr, (3) substrate temperature 600-1 110 O C and (4) gas flow rates up to 800sccm. The result films are characterized by SEM, and unpolarized/ polarized Micro-Raman Spectroscopy. The growth rates, carbon conversion efficiency, film morphology, crystalline quality are summarized varying the growth conditions. Maximum linear deposition rates are over 10udhr under the proper growth conditions. The free standing films are synthesized with a FWHM Raman peak as narrow as 2.7 cin-'.