MPCVD diamond tool cutting-edge coverage: dependence on the side wedge angle

Microwave plasma CVD usually produces uniform diamond coatings and high-quality diamond films. However, abnormal deposits appear near the sample edges - the so-called 'edge effect'. Wedge-shaped silicon nitride inserts with 30 degrees-, 60 degrees-, 75 degrees- and 90 degrees -edge angles were vertically and horizontally exposed to MPCVD diamond coating to systematically study this effect. Finite element method (FEM) analysis was used to simulate the temperature distribution on such geometries. Diamond morphology and quality were assessed by SEM and micro-Raman techniques. The edge effect, a consequence of plasma concentration and thermal phenomena in this experimental set-up (activation by electromagnetic gas discharge), is more accentuated on samples that are vertically wedge-oriented towards the plasma. A grain-size gradient is established along the exposed surface, steeply increasing at the hot edge. An extreme effect occurs in the sharpest wedge samples, avoiding diamond growth at the edge. (C) 2001 Elsevier Science B.V. All rights reserved.