Real-time spectroscopic ellipsometry studies of diamond film growth by microwave plasma-enhanced chemical vapour deposition

Abstract

We have applied real-time spectroscopic ellipsometry to monitor the growth of highly uniform, nanocrystalline diamond films by microwave plasma-enhanced chemical vapour deposition. In this study, a unique multichannel instrument is employed to collect full ellipsometric spectra from 1.5 to 4.0 eV. Here we focus on two capabilities. First, we will describe a method to calibrate the true temperature of the top 200Åof the Si substrate under diamond growth conditions. Second, we describe the full microstructural evolution of the diamond films. The parameters derived include the time evolution of the void and optically absorbing, non-diamond (sp 2) carbon volume fractions in the film. In addition, the nuclei, bulk and surface roughness layer thicknesses during the nucleation, coalescence and bulk growth regimes are determined. These results reveal reproducible and remarkably internally consistent behaviour that provides new insights into the growth mechanisms for nanocrystalline diamond. We find that in the coalescence process, a large volume fraction of sp 2 carbon is trapped in the grain boundaries under all conditions of growth. After coalescence is complete, further generation of sp 2 carbon is impeded under optimum conditions.