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 su
rface have been calculated according to the equilibrium between the adsorpt
ion and desorption of the two precursors at a certain substrate temperature
T-g. The result shows that the H coverage decreases markedly with increasi
ng 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 d
eposited at rather high substrate temperatures may be attributed to the poo
r H coverage on the surface. The value of T-c is determined by H atom conce
ntration n(H) in the reactor. When n(H) is greater than 3.2 x 10(-11) mol c
m(-3), T-c is above 1000 K. The CH3 coverage shows a maximum within the ran
ge of the studied T-s. With the typical CH3 concentrations, the CH3 coverag
e reaches the maximum at T-s similar to 1100 K. A growth rate formula has b
een developed on the basis of the temperature dependent CH3 coverage. The f
ormula 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 ag
reement with the experimental results. (C) 2000 Elsevier Science S.A. All r
ights reserved.