In-situ monitoring of microwave plasma-enhanced chemical vapour deposition diamond growth on silicon using spectroscopic ellipsometry

Abstract

The quality of polycrystalline diamond films is heavily dependent on the nucleation and early stages of growth, making the ability to monitor these early stages highly desirable. Spectroscopic ellipsometry (SE) allows for real-time monitoring of the thickness, composition, and morphology of films with sub-nanometre precision. In this work, ex-situ SE spectra were used to develop an optical model for film characterisation, which was then applied to in-situ data. The coalescence of individual crystallites into a single film was observed through a parabolic decrease in void content followed by peaks in sp2 content and surface roughness. These observations were validated using ex-situ Raman spectra and AFM images of samples grown for durations between 5 and 30 min. The model was also used to investigate the impact of varying the methane concentration, finding that a higher methane fraction resulted in earlier coalescence and a higher peak in sp2 content. This work demonstrates that SE is a powerful tool for monitoring and optimisation of the critical early stages of polycrystalline diamond growth.