Marcus Elliot, MSc Thesis, Jan 2000

'Microwave Chemical Vapour Deposition of Diamond using Methane-Carbon Dioxide Gas Mixtures'

The growth of diamond on Si substrates by microwave CVD has been investigated using unconventional methane-carbon dioxide gas mixtures. This gas composition has been demonstrated to show increased growth rates, with adequate quality.

Experiments have been accomplished to investigate the optimal growth conditions, as a function of composition, pressure and temperature. The plasma has been investigated using optical emission spectroscopy (OES) and in situ Quadrupole mass spectrometry. The thin films grown have been characterised using SEM to examine growth morphology and film thickness, and laser Raman spectroscopy (LRS) to deduce film quality.

Growth quality and optimal growth conditions have been assessed using the information provided by these analysis techniques. The average diamond growth rate is approximately 1 µm h-1. Optimal growth conditions occur at gas compositions of 50% CH4 and 50% CO2. A hypothesized gas phase reaction mechanism is presented. Low temperature growth has been identified with a possible extrapolation down to 400°C.

The temperature of the plasma was also estimated using a two-colour optical pyrometer, by correlating hypothesized blackbody emission from carbon particles i the periphery of the plasma. This temperature was estimated to be ~ 1925nbsp;K.

A research paper based on the OES results has been accepted for publication in Diamond and Related Materials, 2000.