Microwave plasma modelling in clamshell chemical vapour deposition diamond reactors

• Published in: Diamond and related materials 2022-04, Vol.124, p.108917, Article 108917
• Main Authors: Cuenca, Jerome A., Mandal, Soumen, Thomas, Evan L.H., Williams, Oliver A.
• Format: Article
• Language: English
• Subjects: Chemical vapor deposition; Cvd diamond; Diamond films; Electric fields; Electron density; Finite element modelling; Homogeneity; Microwave plasma model; Microwave plasmas; Modelling; Plasma; Polycrystalline diamond; Raman spectroscopy; Resonant frequencies; Sample holders; Temperature distribution; Transient heat transfer
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2022.108917

A microwave plasma model of a chemical vapour deposition (CVD) reactor is presented for understanding spatial heteroepitaxial growth of polycrystalline diamond on Si. This work is based on the TM0(n>1) clamshell style reactor (Seki Diamond/ASTEX SDS 6K, Carat CTS6U, ARDIS-100 style) whereby a simplified H2 plasma model is used to show the radial variation in growth rate over small samples with different sample holders. The model uses several steps: an electromagnetic (EM) eigenfrequency solution, a frequency-transient EM/plasma fluid solution and a transient heat transfer solution at low and high microwave power densities. Experimental growths provide model validation with characterisation using Raman spectroscopy and scanning electron microscopy. This work demonstrates that shallow holders result in non-uniform diamond films, with a radial variation akin to the electron density, atomic H density and temperature distribution at the wafer surface. For the same process conditions, greater homogeneity is observed for taller holders, however, if the height is too extreme, the diamond quality reduces. From a modelling perspective, EM solutions are limited but useful for examining electric field focusing at the sample edges, resulting in accelerated diamond growth. For better accuracy, plasma fluid and heat transfer solutions are imperative for modelling spatial growth variation. [Display omitted] •Experimentally verified microwave plasma model for clamshell diamond reactors•Simple reaction set for computation in COMSOL Multiphysics®.•Plasma fluid models are favourable over electromagnetic models for low pressure•Sample holders affect the microwave fields, plasma shape and temperature profile•The modelled atomic H density correlates with diamond quality in thin films