HFCVD diamond deposition parameters optimized by a Taguchi Matrix

A Taguchi Matrix was used for the experimental design to study the CVD diamond deposition parameters in a cold-wall HFCVD reactor. Gas composition, total gas pressure, total mass flow and substrate temperature were considered as controllable factors, and three levels for each of these factors were selected, in an L9 orthogonal array. A new Figure-of-Merit (FOM) is proposed to assess the best combination of film properties: grain size, residual stress, structural quality and growth rate. Substrate temperature affects mostly grain size and diamond quality, while methane content mostly determines residual stresses and the growth rate. The latter is also mainly affected by the total pressure as well as is grain size, while total gas flow has a neutral effect. Under the limits of deposition conditions, the best FOM is obtained at the highest total gas pressure and mass flow, average CH4 content, and lowest substrate temperature.

Research highlights
► The Taguchi method proved to be a powerful tool for the optimization of deposition parameters of microcrystalline diamond grown by HFCVD method.
► A new Figure-of-Merit (FOM) is proposed based on the Taguchi method to assess the best combination of CVD diamond properties (grain size, residual stress, structural quality and growth rate) within selected deposition condition ranges (total mass flow, total gas pressure, substrate temperature, and methane content).
► The best FOM is obtained at the highest total gas pressure (P = 17.5 kPa) and mass flow (F = 200 ml/min), average CH4 content (2.5 vol%), and lowest substrate temperature (Ts = 750 °C).