Low-pressure chemical vapor deposition (LPCVD) of tungsten (W)
film on silicon (Si) substrate was performed by reducting hexafluoride
(WF6) with hydrogen. This CVD system is known for its nonlinear
dependence of growth rate on WF6 concentration. This study adopted a
simple surface-reaction model which assumes that the precursor, i.e.,
WF6, in the gas phase adsorbs on solid surfaces and then the adsorbed
WF6 molecule is converted into tungsten solid film. The two kinetic
parameters involved in the model are derived from the experimental
results. The solidification rate constant (k
s) is equal to the growth
rate at very high WF6 concentrations. The adsorption rate constant
(k
a) is derived from profile analyses of films grown in microtrenches
under very low WF6 concentrations by applying the conventional Monte
Carlo simulation code, which is valid for linear surface-reaction
systems. In the temperature range of 623 to 823 K, k
a and k
s have
activation energies of 82 kJmol-1, 66.1 kJmol-1, respectively. A newly
proposed Monte Carlo simulation for nonlinear reaction systems, in
combination with the two kinetic parameters, can quantitatively
predict the shape of film in microtrenches for a wide range of
temperatures and WF6 concentrations.
The response of an electron in a hydrogenic nl-orbital to a sudden change in central charge Z → Z + 1 is investigated. This system is taken as a model for the interaction encountered by a Rydberg (spectator) electron when the core atomic system undergoes Auger decay. The most likely outcome is found to be a shake-up to final-state orbitals of quantum number n ≈ √ (Z + 1)/Zn. Calculations are carried out for values of n up to 50. The probabilities for spectator shake-up, shake-down, and no-shake tend to constants for larger n, and are found to be 90.3%, 8.7%, and 1.0% respectively for the Z = 1 case. The probability of shake-off is found to be small, less than 0.3% for low n, and decreasing as n −3 for larger n. The trends found in the hydrogenic case are shown to be in close agreement with Hartree-Fock calculations for the spectator Auger transitions Ar[1s]np → Ar[2p 2 ]mp.
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