Investigation of Large Area HFCVD-Diamond Deposition Processes by Multi-Filament Temperature Measurements

Hot-filament chemical vapor deposition (HFCVD) is a technologically important process for depositing polycrystalline diamond films on large areas or three-dimensional substrates. Growth rate and phase purity of the diamond films are essentially determined by the ability of the hot filaments to produce atomic hydrogen which is affected by the temperature and the state of the filaments with respect to carbon incorporations and carbon coverage, respectively. On the other hand, filament temperature measurements in correlation with deposition parameters give evidence of the state of the filaments and the gas phase activation. A motor driven optical pyrometer system has been built up for precise and fully automatized filament temperature measurements in multi-filament arrangements. This device allows to investigate how the state of each filament in a given setup is affected by integral parameters like gas composition, heating power, pressure etc. and also by local changes of the boundary conditions, for instance due to the positioning of the substrates or to inhomogeneities of the gas feeding system. The presented results demonstrate that multi-filament temperature measurement is a powerful tool for monitoring, controlling, and optimizing large area HFCVD processes. Thus it enables the systematic improvement of reproducibility, homogeneity, and quality of the deposited diamond films.