The dependence of the decay time constant on the chamber size and gas pressure in a pulsed ICP

Summary form only given, as follows. The electron temperature in a pulsed inductively coupled plasma (ICP) can be significantly lowered when it is operated in a pulsed mode. Lower electron temperature, together with the increase in negative ions, was found to be able to reduce notching effects in etching processes. The local plasma properties in a pulsed ICP can be measured by Langmuir probes. The probe current can be measured as a function of delay time for each pulse cycle at different but fixed bias voltages. The current versus delay time data for different bias voltages can then be used to reconstruct the typical I-V curves for each delay time. The plasma density and electron temperature as a function of delay time can then be determined from these I-V curves. For an Ar plasma with a chamber height of 40 cm and diameter of 40 cm, operated at 30 mtorr gas pressure, 13.56 MHz RF, and 10 kHz pulse rate at 50% duty cycle (50 /spl mu/s on and 50 /spl mu/s off), both the temperature and the plasma density were found to decay initially very fast and then much slower in the power off period. The decay time constants are expected to depend on the gas pressure which affects the ionization rate and diffusion coefficient, and also on the chamber size which affects the loss rate of the plasma. Experiments will be carried out for various gas pressures and chamber heights to see how the decay time constants vary with these two parameters.