Etching of CVD diamond surfaces

Abstract

This thesis presents a fundamental study on etching of diamond surfaces. Details of the growth by microwave plasma Chemical Vapour Deposition (CVD) and etching by microwave hydrogen plasma, oxygen reactive ion etching (RIE) and thermal oxidation are presented. Prolonged exposure of {100} diamond surfaces to microwave hydrogen plasma was investigated by atomic force microscopy (AFM). Reduction of surface roughness has been observed while formation of etch pits has not been detected. X-ray photoelectron spectroscopy (XPS) detected the removal of graphitic carbon and reduction of oxygen under hydrogen plasma etching. Electrical sheet resistivity has been observed to be depended on the texture of the CVD diamond films as well as on the ambient exposure time. Both the surface and electronic properties are shown to agree with theoretical models. Formation of columnar structures accompanied the oxygen RIE of CVD diamond films and cubo-octahedral crystallites. Using scanning electron microscopy (SEM) and AFM the preferential formation of columnar structures in the inter-granular area of the diamond films has been detected. Surface contamination by silicon oxide has been identified by EDAX on the diamond surface and specifically on the columnar structures. Analysis by XPS demonstrated that the RIE etched surfaces were oxygen terminated and also were partially graphitised. A discussion on the mechanism of columnar formation has been presented. From the thermal oxidation of cubo-octahedral CVD diamond crystallites the activation energies and pre-exponential factors of the {100} and {111} diamond surfaces were measured, using optical profilometry, to be 221 ± 34 kJ mol-1, 2.3 x 109 nm s-1 Pa-1 and 286 ± 29 kJ mol-1, 1.9 x 1014 nm s-1 Pa-1 over the temperature range 535oC to 600oC respectively. Thermal oxidation of {100} and {111} diamond surfaces was accompanied with the formation of etch pits, increase of surface roughness and the exposure of {113} diamond surfaces between the {100} and {111} surfaces. A mechanism for the thermal oxidation of the diamond surfaces has been proposed.