Experimental characterization of a pulsed ICP discharge

Abstract

Summary form only given. Pulsed low-pressure high-density plasmas attracted a great deal of attention recently owing to their applications in ULSI processing. It has been demonstrated that processing with pulsed plasma can reduce charge-induced damage, such as notching effect. It has been shown that this feature is related to the effect of a reduced electron temperature and an increase of negative ion density during the off period of the pulse. The purpose of this work is to characterize basic properties of a pulsed ICP discharge by employing various diagnostic tools, including a Langmuir probe, a 36 GHz interferometer, an ion energy analyzer, a plasma impedance probe, as well as a monochromator. These tools have been modified from existing ones to measure time-resolved signals associated with a pulsed discharge. Preliminary measurement results show that, in an Ar plasma, electron temperature drops much faster than plasma density. The plasma potential also decreases during the off period because the plasma becomes cooler. The result from the interferometer measurement exhibits a different time dependence of the plasma density from the Langmuir probe data. This is mainly because the former measures the line-averaged values while the latter extracts local properties. In a time-modulated plasma with a typical frequency around 10-100 kHz, there will be a time-delay on the plasma properties, such as density and temperature, at different location in a plasma chamber. As it is averaged spatially, the time dependence is smeared out and exhibits a totally different behavior from the local ones. Further study is being conducted to investigate this issue. Detailed experimental results will be presented.