Measurement and calibration of substrate surface temperature in hot filament chemical vapor deposition

Abstract

The temperature measurement under complex working conditions has always been a challenging task. In this study, taking the hot filament chemical vapor deposition (HFCVD) as an example, the method of measuring the surface temperature of cemented carbide inserts was explored by using K-type thermocouples for contact measurement. Several different thermocouple installation schemes were designed, and an established evaluation system was used as a standard to identify the feasibility of these schemes, including measurement stability, calibration stability, convenience of installation, and cost performance. Finally, the optimal scheme was screened, that is, to insert the temperature measurement segment of a thermocouple into the central through hole of the substrate and keep the tip flush with the surface. It not only protected the thermocouple from being deteriorated by the high temperature gradient field, but also ensured that the thermocouple could sense the heat change that is consistent with the measured substrate surface, improving the stability of the measurement. Noted was that a calibration value should be added to the thermocouple indication value in order to obtain the accurate surface temperature, and thus the measurement and calibrated standard deviations could be controlled as less than 15 °C and 10.81 °C, respectively. The optimal measurement scheme was applied to the actual deposition experiments of diamond films, and the dependence of the coating quality on the temperature was analyzed, which further verified the accuracy of the temperature measurement. This scheme can be extended to other similar complex conditions, including vacuum, large temperature gradient, severe mutual occlusion between objects, or strong chemical reactions.