Paper PS1-TuM1
Radical Concentrations and Temperatures in a Dual-Frequency Capacitive Reactor Determined By Broad-Band UV-Visible Absorption Spectroscopy
Broad-band UV-visible absorption spectroscopy is next in simplicity to optical emission spectroscopy. Unlike optical emission, it provides direct information about ground states of neutral species in plasma environments. However, it has rarely been implemented as diagnostic in industrial plasma reactors. In the present work, we report measurements in a Lam dielectric etch reactor (27/2 MHz dual frequency capacitive) during semiconductor processing using Ar/C@sub x@F@sub y@/O@sub 2@ feedstock gas mixtures. Using a deuterium lamp source and a photodiode array detector we can measure absorption across the 200-260 nm region, allowing simultaneous detection of CF, CF@sub 2@ and SiF@sub 2@ radicals. Other species that we have detected include C@sub 2@ and C@sub 3@. We use the CF radical as example of this technique, and to illustrate the wealth of information easily extracted from moderately high resolution absorption spectra: CF radical ground state number densities are determined with a detection limit of ~10@super 10@ cm@super –3@ using off-the-shelf instrumentation. Typical densities are in the order of 10@super 13@ cm@super –3@ for a standard oxide etch recipe. CF rotational and vibrational temperatures are measured aided by spectral computer simulation code. Typical rotational temperatures, which are normally equivalent to gas temperature in the reactor, are in the order of 425 K. Vibrational distributions, with temperatures of 800 K, show non-thermalization compared to rotational temperatures. We found a previously unreported vibrational band, assigned as CF A-X(3,0), and it is heavily predissociated. Intensities of the CF A-X(v,0) and B-X(v,0) bands are used to determine accurate transition probabilities, enabling precise determination of concentrations and temperatures in future spectroscopic experiments via the CF A-X and B-X bands.