New driving parameters for diamond deposition reactors: pulsed mode versus continuous mode

Abstract

Experimental investigation and modeling of pulsed H2/CH4 plasmas used for diamond deposition are presented. Two plasma configurations are studied : a 2.45 GHz microwave cavity configuration and a 915 MHz surface-wave configuration. Time-resolved measurements of the gas temperature determined from the Doppler broadening of the Balmer ­Ha line, of the H-atom relative density and of the discharge volume (Vpl) are reported. The experimental time-variations of the gas temperature are characterized by a sharp increase at the beginning of the pulse (t 1 ms). The simulations enable us to estimate time-variations of the electron energy distribution function, gas temperature and chemical species densities. The in-pulse steady state temperature obtained from the model is in agreement with the measured one, although a discrepancy is obtained on the shape of the early time-variation. Calculations were carried out in order to study the effects of the in-pulse power, the duty cycle and the off-plasma time on the H-atom and CH3-radical densities. It is seen that, at a constant power density averaged over a period, low duty cycles favor high H-atom and CH3 - radical densities, while too long off-plasma times reduce the H-atom density during the pulse. In addition, the production of H atoms was seen to be governed by thermal dissociation in the 2.45 GHz microwave cavity system, and by electronic impact dissociation in the 915 MHz surface wave system, the latter operating under high gas velocities.

Keywords

• diamond deposition process
• microwave plasma
• continuous mode versus pulsed mode
• key parameters