Earlier Work on Plasma Chemical Processing
Dr. Jae Y. Choe (Ph.D. 1999) and the Inductively Coupled Plasma Reactor.
The focus of this effort was on improving understanding of plasma
etching by probing the surface and plasma during etching. Most studies
were conducted in an inductively-coupled plasma (ICP). Laser-induced
thermal desorption was used to desorb species on the surface and a
gas-phase optical technique, such as laser-induced fluorescence (LIF),
is used to detect the desorbed species. This was used to probe the
adlayer during high-charge-density-plasma etching of Si, Ge, and InP.
The work in this area was a collaborative effort with Dr. Vincent M.
Donnelly of Bell Laboratories, Lucent Technologies (now at the University of Houston) and his colleagues.
For more information see:
Publications, including #67-69, 71, 80, 86, 89, 90, 94, 97, 105, 107, 111 and 115.
"
Optical Diagnostics for Thin Film Processing",
(Academic Press, San Diego, 1996).
Optical Analysis of Surfaces during ICP Plasma Etching using Laser-Induced Thermal Desorption
Plasma chemical etching involves two
competing steps: (1) the chemical transformation of the surface by
neutrals and ions to form surface layers that are more weakly bound
than is the bulk and (2) the removal of this adlayer by ions. The
competition between these two steps produces an surface adlayer.
Knowledge of the composition of this adlayer gives key insight into
understanding the etching process. This composition can be determined
in real time during etching using laser-induced thermal desorption
(LITD), or alternatively laser desorption (LD) to desorb this
weakly-bound surface layer. The desorbed species are monitored by
either one of two methods: laser-induced fluorescence (LIF) or the
transient changes in plasma-induced emission (PIE) caused by electron
excitation of the desobed species; these processses are depicted in the
illustration. Using these techniques, the etching of Si by inductively
coupled plasmas (ICPs) containing Cl2, HBr, Cl2/HBr mixtures and Cl2/O2 mixtures and the ICP etching of Ge by Cl2
have been examined. Other important information is provided by
measuring the etch rate and the composition of the etching plasma (see
below). This work was done by Jae Young Choe and Nicholas Fuller in the
Herman group, in collaboration Dr. Vincent Donnelly of Bell
Laboratories, Lucent Technologies.
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Optical Analysis of Components of ICP Plasmas
Understanding the mechanism of the
plasma etching requires knowledge of the components of the plasma,
including the densities and energy distributions of neutrals, ions, and
electrons. In chlorine inductively coupled plasmas (ICPs), optical
actinometry has been used to determine the absolute densities of
neutral Cl and Cl2 as a function of the rf power delivered
to the ICP coil. The figure below shows that at high powers the Cl
atoms are by far the dominant neutral species. This work was done by
Nicholas Fuller in the Herman group, in collaboration Drs. Vincent
Donnelly and Misha Malyshev of Bell Laboratories, Lucent Technologies.
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