Measurement of the density and rotational temperature of OH in a saturated water vapor slot-excited microwave plasma

Abstract

OH density and rotational temperature were measured in a saturated water vapor slot-excited microwave plasma using spatio-temporally resolved laser-induced fluorescence. The microwave power was 20–100 W under continuous wave mode, whereas 40–200 W peak under pulse-modulated mode (30% duty cycle, 100 Hz). The water vapor pressure was 2.3 kPa. An approximately 2 mm thick flat-shaped plasma was generated on the surface of a slot antenna. The OH density and rotational temperature in the plasma ranged from 1 × 1014 cm−3 to 1 × 1015 cm−3 and from 1100 K to 3000 K, respectively. OH was produced via various routes originating from electron collisions (e + H2O) and was primarily lost through recombination (OH+OH → H2O+O) and diffusion. The production rate (k p ) of OH per H2O molecule, which was calculated based on a simplified reaction model using the measured OH density and temperature, showed a relation of k p / [ H 2 O ] ∝ P 1.8 , where P represents the microwave power. This relationship implies a two-step production process of OH via the vibrational excitation of H2O. Although the OH density increased with increasing microwave power, the density became saturated at high power values.

Improved Uniformity of Photoresist Ashing for a Half-Inch Wafer with Double U-shaped Antenna Structure in a Microwave-Excited Water Vapor Plasma

“…It is assumed that the highest ashing rate achieved by the double U-shaped antenna is attributable to plasma integration and the increased electron density and radical density near the substrate. Laserinduced fluorescence measurement of the H-shaped antenna revealed that the OH radical density at d = 5.5 mm was about 2 × 10 14 cm -3 [33], so the double U-shaped antenna is also regarded as having density on the order of 10 14 cm -3 or more. The OH radical density as well as electron density measurements are the future work to understand the ashing rate difference between the H-shaped antenna and double U-shaped antenna.…”