AVS 46th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoA

Paper PS-MoA3
Comparison of Actinometric and Diode-laser Absorption Measurements of [CF] and [CF@sub 2@] in an Inductively Coupled Plasma Reactor

Monday, October 25, 1999, 2:40 pm, Room 609

Session: Plasma Diagnostics I
Presenter: T.M. Bauer, University of New Mexico
Authors: T.M. Bauer, University of New Mexico
A. Inoue, University of New Mexico
P.-T. Ton-Nu, University of New Mexico
J.L. Cecchi, University of New Mexico
Correspondent: Click to Email
CF and CF@sub 2@ radicals have been shown to be significant precursors for selective oxide etching. Consequently, diagnostics that measure concentrations of these radicals are of interest for process development, monitoring, and control. We compare two such diagnostics: actinometry and wavelength-modulated diode laser absorption spectroscopy. Actinometry is a relatively simple technique. However, it relies on excited state species measurements and may suffer from unwanted influence from other plasma parameters. The diode laser is a more complicated technique, but it provides absolute ground state concentrations. To carry out these comparisons, we have made actinometric and diode laser measurements contemporaneously on an ICP reactor over a pressure range of 10 to 30 mTorr and rf power range of 200 to 1000 W. Gas feedstocks included C@sub 2@F@sub 6@, CHF@sub 3@, and CF@sub 4@, each with 10% Ar added as an actinometer. Over these ranges, the CF concentration varied from 8x10@super 12@ to 4x10@super 13@ cm@super -3@, as determined by the diode laser. The CF@sub 2@ concentrations ranged from 5x10@super 13@ to 9x10@super 14@ cm@super -3@. Our results indicate that for CF@sub 2@ concentrations greater than 8x10@super 13@ cm@super -3@, the actinometric measurements are proportional to the absolute concentrations measured with the diode laser system, with the same constant of proportionality for all feedstocks and over the entire operating range. For CF@sub 2@ below 8x10@super 13@ cm@super -3@, we observe some deviation of the actinometric data, possibly due to interference from other features in the spectrum. For CF, we find that actinometric measurements are proportional to the absolute concentrations measured by the diode laser as a function of power, however, the constant of proportionality depends strongly on pressure and to a lesser extent on the feedstock. We believe that this reflects an underlying dependence of the CF actinometric signal on electron temperature.