Fundamental studies of diamond chemical vapour deposition : plasma diagnostics and computer modelling

• Main Author: Richley, James Christopher
• Published: University of Bristol 2011
• Subjects: 671.735
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.550307

This thesis reports experimental studies of the gas-phase chemistry within microwave plasma en- hanced (MWPE) reactors used for the chemical vapour deposition (CVD) of diamond, as well as computational investigations into gas-surface and surface based chemical reactions which are likely to play a role in the growth and morphology of diamond films. A combination of cavity ring down spectroscopy (CRDS) and optical emission spectroscopy (OES) has been applied to study CH4/H2/Ar plasmas which contain a high proportion of Ar (~86.8%). Column densities were successfully measured for C/a) and CH(X) radicals, and for H(n=2) atoms as a function of height above the substrate, and for a range of process conditions (power, pressure, flow rates, etc. ). Addition of Ar was found to have a large effect on the plasma's capacity to absorb the microwave power, which in turn resulted into a substantial increase in the plasma volume. Variation of the Ar fraction within the input gas mixture was found to have little effect on the average rotational temperatures derived from C/a) absorption, however. CRDS has also been applied to study B atoms within B2H6~/ Ar and B2HJCH4~/ Ar plasmas. Column densities as a function of process conditions as well as their spatial profile were successfully measured. B atoms were found to be extensively distributed throughout the reactor volume spanning much wider regions than species like CH and C2 radicals. Electronically excited species within CO/CH/H2 plasmas have been studied using OES. Spatial distributions of their emissions, as well as changes as a result of process conditions, have been mea- sured. Preliminary CRDS measurements of C2(a) and CH(X) column densities in these plasmas are also presented. Quantum mechanical (QM) and Quantum mechanical/Molecular mechanical (QM/MM) studies have explored insertion reactions of CxHy (x=0-3, V=0-2), B atoms and BH radicals directly into C-H and C-C bonds on the diamond surface. Insertion of several of these species into C-H bonds on the diamond surface was found to be energetically feasible at typical growth temperatures. Such insertion reactions may play a role in diamond growth and/or doping, and serve to complement more traditional growth mechanisms, based on radical addition to surface radical sites. QM/MM studies have also explored the migration of CH2 and BH groups on and between the reconstructed 2 x 1 {lO0} and {111} H -terminated surfaces.