Study of microwave discharge at high power density conditions in diamond chemical vapor deposition reactor by optical emission spectroscopy

Abstract

The paper presents results of measurements of spatial distributions of emission intensity of various lines of argon, atomic hydrogen, C2 and CH molecules in a wide pressure range from 40 to 500 Torr in diamond chemical vapor deposition (CVD) reactor. Microwave discharge plasma was maintained in reactor in continuous mode both in hydrogen and in a mixture of hydrogen-methane with a small addition of argon for diagnostic purposes. Intensity distribution of argon emission was characterized by a pronounced maximum near the substrate in reactor, which indicates that microwave power density (MWPD) absorbed in the plasma is also concentrated mainly near the substrate. Maximum emission intensity of hydrogen atoms is located at some distance from the substrate, and maxima of spatial distributions of emission intensity of carbon-containing species C2 and CH are shifted farther away from the substrate. This leads to the fact that the shape and size of discharge, which are observed visually or with help of a camera, significantly differ from the distribution of MWPD. There is a difference in the shape of spatial distribution of argon lines emission (750.4 nm and 811.5 nm), that can be explained by a change in the mechanism for quenching the excited levels of argon in different regions of discharge. This imposes some restrictions on the use of argon for measuring characteristics of microwave discharge.