Studies in microwave and RF capacitively coupled excimer lamp

摘要

A lamp that emits strongly in the 180--200 nm region is desirable because of the response of organic materials in this wavelength range. Therefore there is the demand for high-powered, efficient, and low-cost UV and VUV sources.;The purpose of this work is to construct and study two novel (low-cost) UV sources and to understand the (1) emission (180--200 nm) characteristics, (2) electron energy and (3) temperature distribution in the plasmas generated by these two novel excimer lamps.;We designed, constructed and studied (1) a probe-coupled 2.45 GHz microwave arrangement to drive Xe and KrI excimer lamps and (2) a 13.45 GHz RF capacitively coupled arrangement to drive Xe/XeAr excimer lamps. In the 2.45 GHz microwave drive, the Xe electrical efficiency and output power in the 160--200 nm range both increased with pressure and input power up to 1500 torr and 600 W (42.5 W/cm3) respectively. For the KrI discharge, over the pressure range of 50--100 torr, more than 80% of the emission was in the wavelength range 170--190 nm. Model calculation that takes into account the angular distribution of intensity and experimental measurement of the angular distribution of emission find considerable intensity well away from the surface normal. The calculated efficiency varied from 20 to 40% for the Xe and 8 to 20% for the KrI depending on pressure giving for the first time good agreement between theoretical calculations and experimental measurements of excimer lamp performance. Over the pressure range studied, the highest output power was ∼0.96 W/cm2.;The 13.56 MHz lamp arrangement was used to produce a bright, halogen-free light in the 180--200 nm range. At input powers of >500 W and pressures >500 torr, more than 80% of the emission appears in the spectral region between 180 run and 200 nm with a strong 193 nm emission due to energy transfer mechanism between Ar and Xe. The estimated electrical efficiency is 15--20%, taking into account the angular distribution of the light intensity. Output power increased with increasing pressure up to 1500 torr. Cooling with liquid nitrogen boil-off rather than room air more than doubled the optical output power for fixed input power.;We used an RF fluid model to calculate the plasma electron density and electron temperature distribution along the length of the discharge bulb. Our results indicate that the electron density and temperature distribution along the length of the bulb is constant. Electron density is an important plasma parameter; it determines the rates of production of reactive species and ions and provides basis for monitoring and real-time control.