Three-Dimensional Measurements of Fundamental Plasma Parameters in Pulsed ICP Operation

Radio frequency inductively coupled plasma sources are widely used in low temperature industrial processing. Having reached a limit in process improvement available with steady state plasmas, the semiconductor industry is turning to temporal modulation of the rf generators in these sources. We conduct experiments in a modified industrial etch tool with pulsed Argon plasma
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. Three-dimensional volumetric measurements were done using a computer-controlled probe drive. The ICP are supplied by a radio frequency source at 2 MHz and can be pulsed at arbitrary repetition rates and duty cycles. The magnetic field was measured using a three-axis magnetic probe (Bdot). A hairpin resonator probe was used to measure local electron density and a swept Langmuir probe was used to measured electron distribution functions. At low pressure, the plasma starts with residual plasma from the previous pulse and evolves into a “ring” shape density profile. Subsequently, the profile peaks in the middle of the chamber as it reaches a steady state toward the end of the active-glow phase. At higher pressure, the plasma density profile peaks at the center of the chamber throughout the entire pulse.