Feedback control of the substrate surface temperature in a laser-induced plasma CVD process

A laser-induced plasma chemical vapour deposition (LPCVD) process is used for the deposition of CVD diamond coatings. For the CVD diamond deposition, the surface temperature of the substrate has to be between 900 °C and 1200 °C, but already small temperature variations influence the crystal structure and the growth rate. To ensure the reproducibility of such a deposition, a feedback control of the temperature was developed. The surface temperature, measured by a pyrometer, and the temperature of the backside of the sample, measured by thermocouples, were used for the input to the control. For the feedback control, a combination of the two temperature measurements was used to regulate the laser power.