Yk. Chae et al., EXPERIMENTAL AND NUMERICAL-ANALYSIS OF RAPID REACTION TO INITIATE THERADICAL-CHAIN REACTIONS IN WSIX-CVD, Thin solid films, 320(1), 1998, pp. 151-158
Gas-phase reactions leading to radical chain reactions of tungsten hex
afluoride (WF6) and silane (SiH4) in tungsten silicide (WSix) chemical
vapor deposition (CVD) were studied using a hot-wall tubular reactor.
To prevent film growth being limited by gas-phase diffusion or by sur
face reactions, a reactor diameter from 2.4 to 4 mm and pressures from
0.5 to 10 Torr were used. To extend the reaction zone to permit detai
led measurement of the axial film growth-rate profile, relatively high
axial flow velocities from 6 to 19 m s(-1) were used. A two-dimension
al numerical simulation was used to improve the accuracy of the analys
is. The measured overall reaction rate, r, was independent of pressure
and reactor diameter, indicating that it could be expressed by a simp
le first-order reaction of WF6, r = k(gr) C-WF6, where C-WF6 is the WF
6 concentration. An Arrhenius plot of k(gr) gave an activation energy
of 28 kJ mol(-1). This relatively small activation energy confirms tha
t the gas-phase reactions are controlled by radical chain reactions. T
he experimentally observed behavior that the reaction rate was indepen
dent of SiH4 concentration may suggest that SiH4 does not participate
in the elementary reaction that activates WF6. One possibility is that
thermal decomposition of WF6 limits the initiation reaction. (C) 1998
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