Gas convection caused by electron pressure variations in pulsed discharge
Résumé
Neutral gas temperature (Tg) is measured in an industrial high-density inductively coupled etch reactor operating in CF4, SF6, O2, Cl2, or HBr plasmas. Two laser diodes are used to deduce Tg from the Doppler widths of 772.38 and 811.5nm lines absorbed by Ar∗(P23) metastable atoms, when a small amount of argon (5%) is added to the gas flow. With the 811.5nm beam passing parallel to the wafer, Tg near the wafer surface is obtained by laser absorption technique. With the 772.38nm beam entering the top of the reactor perpendicular to the wafer surface, the volume averaged temperature is deduced by laser induced fluorescence technique. The volume averaged Tg increases with radio frequency power and with pressure, although the temperature near the walls is only weakly dependent on gas pressure. The main effect of increasing the pressure is an enhancement of the temperature gradient between the discharge center and the wall boundary. Due to the thermal accommodation, the authors always observe a significant temperature jump between the surface and the gas in its vicinity. This gap is typically about 200K. Gas temperatures for a wide range of pressure and rf powers are reported. These data will be useful to validate and improve numerical models of high-density reactive plasmas.