Growth mode evolution and quality improvement of CVD diamond growth: role of substrate orientation

Abstract

The effect of misorientation angles of diamond substrate on the epitaxial diamond layer grown by microwave plasma chemical vapor deposition (MPCVD) has been investigated. The surface morphology, impurity incorporation and dislocation density of epilayer are significantly influenced by the misorientation angels of diamond substrate along to the <110>. Herein, the substrate with 3–4° miscut angles is considered to be most suitable for deposited diamond layer, which enables to grow the high-quality crystal exhibiting macroscopically flat surfaces while effectively suppressing unintentional impurity incorporation. The dominant growth mode of diamond surface undergoes from island-growth mode to two-dimensional (2D) lateral growth mode and finally to step-flow growth mode. It is also found that the morphological features of hillock defects transit from pyramidal to triangular, attributed to reduced C-species adsorption on hillock surfaces and sustained step-flow advancement. The introduction of misorientation angles changes the nucleation process and growth kinetic characteristics of hillocks. The growth rate of flat surface increases and the number of surface hillocks decreases significantly. The growth rate increases from ∼3 μm/h to ∼9 μm/h. The density of hillocks is decreased from ∼300 cm⁻² to 0. Meanwhile, the average density of etching pits decreases from ∼10⁵ cm⁻² to ∼10⁴ cm⁻² with increasing off-axis angles. Based on crystal growth theory and Burton-Cabrera-Frank (BCF) theory, the relationship between the diffusion dynamics of C atoms and the misorientation angle is discussed. The substrate orientation promotes the adsorption process of C atoms at edge sites and changes the surface diffusion distance to achieve a flat surface, elucidating the underlying mechanism for angle-dependent control of surface morphological evolution.