Local concentration focusing effect on deposition efficiency caused by inlet of fluids in MPCVD reactor

Abstract

Microwave Plasma Chemical Vapor Deposition (MPCVD) has emerged as a prominent technique for advanced material synthesis, particularly diamond growth, characterized by inherently complex multiphysical phenomena. At moderate gas pressures (on the magnitude of 0.1 atmospheric pressure), flow effects play a substantial role in MPCVD reactors. However, most previous studies choose to neglect these flow characteristics due to huge computational challenges in multiphysical modeling. Empirical evidence has demonstrated that strategic modifications to fluid inlet configurations may enhance diamond deposition rates by an order of magnitude, yet the underlying mechanisms remain inadequately understood. This study implements a comprehensive multiphysical modeling framework incorporating coupled electromagnetic field, plasma field, flow field, and temperature field. Special attention is given to plasma characterization as a multi-component system requiring rigorous treatment through Maxwell–Stefan diffusion theory. However, previous theoretical analysis reveals a critical limitation in conventional Maxwell–Stefan implementations, which is the inherent assumption of inviscid flow. This contradicts the viscous nature of MPCVD operational environments, as evidenced by our simulation results, demonstrating the necessity of viscous diffusion integration in heavy species transport to achieve experimental consistency. The inclusion of viscous diffusion mechanisms reveals enhanced hydrogen atom concentration near substrate apertures through inlet-induced flow modifications. This concentration enhancement directly correlates with improved deposition rates as per the Goodwin–Harris model. Our findings establish that viscous diffusion constitutes a previously overlooked yet critical transport mechanism in MPCVD reactors, complementing conventional mass diffusion and convective transport. This revelation provides new fundamental insights into diamond deposition mechanisms and proposes a novel process optimization paradigm through transport manipulation.