Microwave analysis of PACVD diamond deposition reactor based on electromagnetic modelling

摘要

The production of high quality diamond films by microwave plasma assisted CVD, with rapid growth rates and good uniformity over large surfaces, requires perfectly optimized reactors from the microwave deisgn point of view. Most MW plasma assisted CVD reactors used for diamond film deposition work on the resonant cavity principle. The design of such reactors relies on 3 choices: i) choice of a suitable resonant mode (i.e. with an electric field structure conducive to plasma ignition), ii) choice of a MW coupling system to excite the cavity, and iii) choice of a quartz window to delimit a reduced pressure zone inside the cavity, so as to obtain the plasma in front of the substrate [1]. In this paper, we present an analysis method for MW plasma reactors relying on EM modelling, which allows for the identification of a resonant mode responsible for plasma ignition, applied to an existing reactor exhibiting plasma instabilities and requiring constant supervision. This analysis method, which can be generalised to any resonant cavity reactor, can describe the device behaviour (shape and location of the plasma, occurrence of instabilities) as a function of the variours cavity geometrical configurations and to get a first estimate of the process performance. On the basis of such an analysis, it was possible to propose modifications to the reactor considered in order to improve process stability, and obtain higher growth rates. First growth tests done on diamond mono- and nano-crystalline films show excellent material quality and an increase in growth rate by more than an order of magnitude.