ISSN:
1572-8986
Keywords:
SiH4
;
SiH4−H2 mixtures
;
electron energy distribution function
;
rf discharges
;
modulation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Technology
Notes:
Abstract Electron energy distribution functions (EDF) in SiH4, SiH4−H2 radiofrequency discharges have been calculated by solving the time-dependent Boltzmann equation in the presence of a sinusoidal field. Particular emphasis is given to the modulation of EDF as a function of the applied frequency (π·106≤ω/p 0 ≤π·108 sec−1 torr−1) and of gas composition. The results show that at ω/p 0 = π·106 sec−1 torr−1 EDF follows in a quasistationary mode the variation of the field with the exception of a small range of electric field near to the zero crossing. Still, at the higher considered frequency (ω/p 0 =π·108 sec−1 torr−1), we observe some modulation of EDF. The necessity of using a time-dependent approach is tested by comparing the present results with the corresponding ones obtained by using the effective field approximation (i.e., the approximation which solves instead of the time-dependent Boltzmann equation the corresponding stationary one at the effective values $$E = E_o /\sqrt 2$$ of the rf field). The two sets of results can differ by orders of magnitude in the tail of EDF, the differences decreasing with increasing molar fraction of H2 and increasing field frequency. The role of excited states (second-kind collisions) is studied by inserting in the Boltzmann equation given concentrations of vibrational and electronic states. The results show that second-kind collisions strongly affect EDF especially in pure silane. Finally a satisfactory agreement has been found between theoretical and experimental results concerning the modulation of electrons of given energy in pure silane discharges.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01016057
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