LIF measurement of ion motion above and in a sheath in a pulsed industrial plasma etch tool

Knowledge of the behavior of ions in the plasma are essential to the process of industrial etching. We studied the motions and energy distribution (IEDF) of argon ions in a 2 MHz inductively coupled plasma (ICP) etching tool, measured by laser induced fluorescence (LIF). A silicon wafer at the bottom of the machine can be biased with a 1 MHz 1.2 kV peak-to-peak sinusoidal voltage. The bulk plasma is formed with a 2 MHz ICP coil which, along with the wafer bias, can be pulsed on and off within 50 microseconds.. The experiment compares the cases of ion motion with and without wafer bias. For both of these cases the two dimesional flow pattern of low and high energy ions is studied near the center and edge of the wafer. Significant vorticity is observed near the wafer edge. When the bias and ICP coil are powered simultaneously the IEDF has a tail that stretchs from low energy to the wafer bias voltage. Experiments in which the wafer is biased in the afterglow, that is when the ICP is off, result in a IEDF with a narrow distribution of energy close to the bias voltage. In both cases the IEDF as a function of location on the wafer and height above it are presented. The angles at which ions strike the wafer are presented in both cases..