Energy Transport and Frequency Dependent Ion Kinetics in a Capacity Coupled Plasma Reactor

Precision plasma etching of microelectronics features requires exquisite control over the
uniformity of the plasma across the wafer and of the ion energy distributions (IEDs) striking the
surface. The IEDs influence etch rate and direction, surface roughening and critical dimension
variations. IEDs also provide insights into spatially dependent energy deposition and flow within
the plasma. Hot neutrals and ions may influence dissociation, ionization, detachment and surface
processes in gases containing molecular species. Thus understanding and possibly controlling the
temperature of plasma species may provide a way to tailor the chemistry in reactive gas systems.
The focus of our experimental work is the measurement of ion temperature (TI), drift velocity
and relative density across a 300 mm wafer in argon plasmas driven at rf frequencies between 13
and 162 MHz. Spatially-resolved, non-perturbative laser induced fluorescence (LIF)
measurements of the argon ion metastable lineshape yield information on TI and IEDs, ion density
and drift velocity, energy deposition mechanisms, charge exchange reactions, neutral heating, and
plasma potential gradients. We find that the ion density increased linearly with rf power, as did the
electron density, indicating that the ion metastable state is formed from direct impact ionization. TI
was ≈500 K, consistent with other capacitively coupled systems at 13 MHz but considerably less
than in inductively coupled systems (1000 – 9000 K). With large chamber size and high excitation
frequencies (162 MHz), electrode dimensions are no longer small compared with the rf excitation
wavelength, and so electromagnetic spatial effects and standing waves become important.
Dr. Gregory A. Hebner received his BS, MS and PhD in Electrical Engineering from the University
of Illinois. He joined Sandia National Laboratory in 1989 and is now Manager of the Lasers,
Optics, Remote Sensing, Plasma Physics and Complex Systems Department. Dr. Hebner's
research addresses development of novel plasma diagnostics using optical and microwave
techniques focusing on understanding fundamental plasma physics and chemistry issues in
technologically relevant gases. He has led many research activities, including programs in nuclear
pumped lasers, plasma crystals and plasma etching sources. Dr. Hebner is a Fellow of the
American Physical Society and the American Vacuum Society, and recipient of the AVS Plasma
Science and Technology Division Prize and the DOE Weapons Award for Excellence.