Influence of nucleation parameters on growth of diamond thin films by hybrid hot filament CVD

Abstract

Diamond thin films have been deposited using a modified hot filament CVD method involving a dual-plasma reactor arrangement. This new design allows ignition of d.c. plasma above and/or below the hot filaments. Thus, substrate bombardment by ions could be realized in the reverse biasing at as low voltages as 50 V. Ion current density and dose could be controlled by the plasma formed above the filaments and grid placed above them. Ion current density seems to be a dominant factor in achieving of homogenous nucleation at low substrate bias. The influence of nucleation time and substrate bias on film quality has been investigated by Raman spectroscopy, X-ray diffraction measurements and scanning electron microscopy. Continuous films have been nucleated at a bias voltage of 120 V and higher. The polycrystalline diamond showed a change of preferential grain crystallographic orientation from (1 0 0) to random orientation with increasing bias. Twinning of diamond grains and nucleation degradation was observed for a substrate bias of 160 V and higher due to high-energy ion bombardment of the substrate. Size of diamond grains and film thickness decreased with increasing nucleation bias. Correlation between the time dependence of total substrate current and Avrami's model is discussed.