A chemical adsorption growth model for hot filament chemical vapor deposition diamond

Abstract

In this paper, a chemical adsorption model for hot filament chemical vapor deposition (NF-CVD) of diamond films has been proposed based on some recent experimental data. The coverages of H and CH3 precursors on the growing surface have been calculated according to the equilibrium between the adsorption and desorption of the two precursors at a certain substrate temperature T-g. The result shows that the H coverage decreases markedly with increasing T-s when T-s is over a critical temperature T-c. Below the temperature T-c, it comes close to 1. Thus, the quality deterioration of diamond films deposited at rather high substrate temperatures may be attributed to the poor H coverage on the surface. The value of T-c is determined by H atom concentration n(H) in the reactor. When n(H) is greater than 3.2 x 10(-11) mol cm(-3), T-c is above 1000 K. The CH3 coverage shows a maximum within the range of the studied T-s. With the typical CH3 concentrations, the CH3 coverage reaches the maximum at T-s similar to 1100 K. A growth rate formula has been developed on the basis of the temperature dependent CH3 coverage. The formula shows that the growth rate follows the Arrhenius law at relative low T-s, but it rapidly decreases when T-s is rather high, which is in good agreement with the experimental results. (C) 2000 Elsevier Science S.A. All rights reserved.