LASER INDUCED FLUORESCENCE DIAGNOSTICS OF GLOW DISCHARGE PROCESSES GAS TEMPERATURE AND RADICAL CONCENTRATION MEASUREMENTS IN A $CCI_{4}$ PLASMA REACTOR
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Date
1982
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Ohio State University
Abstract
Plasma chemistry is widely employed in the electronics industry as a means of fabricating microdimensional circuit features. However, few plasma reaction mechanisms have been characterized even partially because the discharge chemistry is complex and easily perturbed by intrusive analytical techniques. Simple emission spectrascopy has proven useful as a non-intrusive qualitative $probe^{1}$ but has not yet been utilized in a quantitative fashion. We report a laser induced fluorescence (LIF) study of a $CCI_{4}$ discharge, used in Al, Si and HI-V etching. CCI radical LIF $(A^{2}\Delta - X^{2}\Pi)$ is spatially resolved in order to obtain concentration and temperature profiles as a function of RF power, pressure, flow rate, electrode temperature, and feedstock composition. Comparison of LIF determined concentration profiles with emission intensity profiles demonstrates that although emission is sometimes a useful qualitative diagnostic, it is rarely quantitatively accurate. For example, when up to 15% $O_{2}$ is added to the feedstock. CCI emission remains unchanged but CCI density decreases by 22%. When total pressure is varied from 0.1 to 1.0 Torr, at constant power, both CCI emission and density go through maxima but at slightly different pressures; these maxima are approximately coincident with a minimum in applied voltage, indicating a strong current dependence to the production of both excited and ground state CCI. Both emission and LIF show structure as position is scanned along the electrode axis. Finally it is found that gas phase CCI concentrations and rotational temperatures are sensitive to electrode temperature, particularly at low power densities $(\leq 0.2 W cm^{-3})$. This temperature effect leads to the conclusion that CCI is a precursor to polymerization in $CCI_{4}$ discharges.
Description
${}^1$ W. R. Harschbarger, R. A. Porter, T. A. Miller, and P. Norton, App. Spectruse, 31, 201 (1977).