Distributions of absolute C2 and C3 densities in low-pressure, high-density C_4F8 plasmas measured by broadband absorption spectroscopy combined with laser-induced fluorescence
Abstract
Deposition of neutral radicals plays important roles for the selective etching of SiO2 using fluorocarbon. To date, many works have been carried out for the diagnostics of CFx radicals in fluorocarbon plasmas. In the present work, we measured distributions of absolute C2 and C3 radical densities in low-pressure, high-density C_4F8 plasmas excited by helicon-wave discharges. The absolute densities of C2 and C3 were evaluated by broadband absorption spectroscopy using a Xe. The spatial distribution of relative C2 and C3 densities were measured by laser-induced fluorescence. The distributions of the absolute densities were determined by combining the two measurements. For the accurate determination of the absolute densities, we measured the rotational temperature of C2 by laser-induced fluorescence. Plasmas were produced at rf powers of 0.6 ∼1.4 kW and C_4F8 pressures of 2 ∼10 mTorr. The C2 radical density was on the order of 10^11 cm-3 at the center of the plasma column. It increased with the distance from the center, and was higher than 1 × 10^12 cm-3 at a distance of 8 cm from the center of the plasma column. Spatial distribution of the C3 radical density was also hollow, and its absolute density was one-order of magnitude lower than the C2 radical density.
- Publication:
-
APS Annual Gaseous Electronics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..GECGTP066A