Interaction of an Excimer-Laser Beam with Metals. Part III: The Effect of a Controlled Atmosphere in Laser-Ablated Plasma Emission

Abstract

The effects of pressure over the range 10 to 760 Torr and of atmosphere (air, argon, and helium) on an ArF-excimer laser ( λ = 193 nm) ablated plasma created above the surface of a copper target was studied with the use of emission measurements. These factors greatly influenced the shape, line-to-background (L/B) ratio, and temperature of the plasma. In general, the size of the plasma decreased with increasing pressure. In air or argon, and at pressures less than 50 Torr, the plasma consisted of two distinct regions. With the use of neutral copper [Cu(I)] lines, reduced pressure from 760 to 10 Torr resulted in a 7-fold increase in air and an 11-fold increase in an argon atmosphere. With the use of a helium atmosphere, the maximum line intensity was obtained at 50 Torr. This was a 1.5-fold increase over that obtained at 760 Torr. With a reduction in the pressure in air or argon, the position of maximum intensity (for copper atom and ion lines) moved away from the surface. For helium, the position of maximum intensity did not significantly vary in accordance with a reduction in the pressure. In general, the plasma temperature decreased with decreasing pressure.