CVD boron nitride films have been deposited at 800 °C from
diborane, ammonia, and hydrogen gas mixtures,
using different B2H6 flow rates. The
effect of the [B2H6]/[NH3]
ratio in the gas mixture on the structure,
composition, and the stability of the layers in humid atmospheres has
been studied. For low
[B2H6]/[NH3]
ratios (r ≤ 0.25), the deposition rate is low and some
crystalline ordering in the deposit was detected.
However,
when ratios >0.25 are used, stable amorphous boron nitride films are
deposited at deposition rates four times
higher (160 nm min-1). The partially turbostratic
boron nitride films, deposited at r ≤ 0.25, are unstable
in
humid atmospheres (80% moisture). The evolution of the unstable
films was followed by infrared spectroscopy.
It is observed that the turbostratic component in the film is
rapidly attacked by the water molecules present
in the atmosphere, giving rise finally to boron enrichment in the
films. After this stage, the attack rate becomes
slower, due to the higher stability of the amorphous component in the
films.
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