Laser initiation and radiofrequency sustainment of seeded high pressure plasmas

Summary form only given. Laser initiation of a low ionization seed (2-6 mTorr) gas in high pressure(>10 Torr) gases is examined. An excimer laser operating at 193 nm is used to initiate a high density, low ionization energy (6.1 eV) organic seed gas plasma of 10/sup 13///cm/sup 3/ and a low electron temperatures of <0.3 eV. This large volume plasma of 300 cm/sup 3/ is used to provide enhanced inductive coupling for moderate power radiofrequency sustainment at high gas pressures consisting of nitrogen and argon mixes. We have obtained high density radiofrequency (RF) discharges with line-average densities of 9/spl times/10/sup 13//cm/sup 3/ and volumes of 500 cm/sup 3/ with 2.5 kW of 13.56 MHz RF power alone at 10 Torr. We are examining the use of laser initiation and nitrogen/argon gas mixes to reduce recombination losses at this and higher pressures and RF power levels to minimize radiofrequency sustainment power requirements. We have also obtained laser initiated, RF sustained discharges at RF power levels which are much lower than required to initiate the high pressure discharge with radiofrequency alone. We are examining these techniques at high pressures(>100 Torr) to determine optimum gas mix and RF power requirements for producing high density plasmas in high pressure conditions. We utilize mm wave interferometry, optical spectroscopy and antenna loading impedance measurements and analyses to determine the ionization and recombination processes occurring in the high pressure discharges. The influence of the laser/RF timing and power levels, gas mixes as well as density and spectroscopic data are used to determine the ionic constituents and plasma decay processes for the high pressure plasma discharges.