VizGlow Application Note
Simulation of Inductively Coupled Plasma (ICP) Reactor with Large
Process Gas Chemistries
Plasma processing reactors areExternal faraday cageused to accomplish a variety of unit
steps in a semiconductor integrated
circuit manufacture. In most cases,
Inductive coils
complex feed gas mixtures are used
in a plasma reactor to realize
Plasmaprecise etch, deposition, doping,cleaning and other types ofQuartz wall
processes. The VizGlow Plasma
Modeling Software Package provide
Wafer holder
capability for modeling plasma
reactors with complex reactiveplasma chemistries in the gas phase
Figure 1: Geometry and mesh for dome-shaped
and at reactive surfaces.
This
Inductively Coupled Plasma (ICP) reactor.
technical note discusses thesimulation of a hydrogen bromide (HBr) plasma in a dome-shaped Inductively Coupled Plasma(ICP) reactor representative of several real industrial reactor systems. HBr gas and mixtures ofHBr with other gases are used commonly in the anisotropic etching of silicon-based materialsurfaces.
Figure 1 shows the geometry and mesh for the plasma reactor simulation discussed in thisnote. The geometry is represented by6 subdomains (plasma, dome-shaped quartz wall,inductive coils, external Faraday cage in which the coils are present, the wafer holder, and awafer edge focus ring). The radius of the reactor quartz dome wall is 20 cm with a 200 mm dia.
wafer. The inductive coil system comprises 20 turns. The mesh comprises a total of about
28,000 cells in the domain.
The pure HBr plasma is generated by driving 2 kW of power through the inductive coils with460 kHz radio-frequency (RF) excitation. The HBr plasma is represented by 15 species (E, Br+,Br2+, HBr+, H+, H2+, Br-, Br, Br2, Br*, Br2*, H, H2, H*, HBr)and 51 reaction. The reaction
mechanism includes electron impact dissociation, excitation, and ionization reactions,attachment reactions for negative ion formation, ion-neutral reactions, ion-ion reactions, andreactive neutral chemistries. The surface chemistry is represented by simple quench

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chemistries for all reactive ions and radicals to form
their corresponding stable neutral species which arethen injected back into the plasma.A pressure of 5mTorr is assumed for the simulations.
The complete model representation of the reactor
is provided by inductive wave physics, plasma dynamics
and reactive plasma chemistries. The electromagnetic(EM) wave frequency domain solver from the VizEM
Electromagnetics Modeling Package is solved in acoupled fashion with the core VizGlow package. The
EM wave generated by the coils is Epolarized, meaningthat the only non-zero component of the wave E field isin the direction perpendicular to the domain
representation.
The high-density HBr plasma isrepresented using the quasi-neutral formulation. Aflow residence time formulation is used to represent
the effect of gas flow in the reactor. The plasma gasFigure 2: Electromagnetic wave field
phase and surface chemistries are managed by thein the reactor. (Top) real andGasact and Surfact modules within VizGlow. Results at(Bottom) imaginary part of the Esteady-state are reported here. A steady-state is foundpolarized magnetic vector potential.
to be achieved in about 2 milliseconds of physical timein the simulation. This time corresponds to the ion
ambipolar diffusion time scale for the reactor geometry. Figure 2 shows the real and imaginaryparts of the magnetic vector potential of the Epolarized EM wave.
Figure 3 shows the EM wave power absorbed bythe plasma.
The wave power absorption isdetermined by the plasma conductivity (determinedby plasma electron density and electrontemperature) and the magnitude of the wave
electric field. For the relatively low excitation
frequency of 460 kHz, the skin depth of the plasma issufficiently large that EM wave power is absorbed
relatively deep within the plasma, away from thequartz dielectric wall.

Figure 3: EM wave power absorbed by
the plasma.

Figure 4 shows the structure of the plasma as
identified by the dominant charges species in the plasma. Under the condition chosen for thesimulation the plasma is largely electropositive (meaning that the negatively charged ion
densities are much smaller than positively charges ion densities). The peak electron (E)densities are located on the axis of the reactor and have a magnitude of 5x1016 m-3. The
dominant ion is Br+ which has a spatial profile and magnitude similar to the electrons. The HBr +Copyright © Esgee Technologies Inc.

| www.esgeetech.com| VizGlow version 1.8 (Feb 2012)ions are also shown in the figure and have a peak
profile that is off the reactor axis. Note that theelectron and other charges species peak at locations
that are far from the location of the EM wave power
absorption peak which occurs close to the quartz
dielectric wall (see Fig. 3). This has to do with thenon-local nature of the plasma at the very lowpressure of 5 mTorr.

Figure 5: Dominant charged species fluxes to thewafer surface.

Figure 5 shows the radial profiles for the dominantcharged species fluxes to the wafer surfaces. This
information is important to determine the uniformity
Figure 4: Charged species densityof the process at the wafer. The dominant ion is Br +profiles in the dome-shaped ICP
whose radial profile is relatively uniform throughout
reactor.
the radius of the wafer with slight non-uniformity
seen at the edge of the wafer. Other ions such as HBr+ have much lower flux to the wafersurface.
In summary, the VizGlow Plasma Modeling Software Package provides a wide range ofphysical models and options that allows one to simulate complex coupled phenomena that areencountered in most plasma discharges. The VizGlow Plasma Modeling Software Package ispart of the Overviz framework suite which provides an intuitive interface to set-up a project tobe solved using VizGlow, manipulate multiple projects for parametric studies. VizGlow isprovably fast, robust, and easy-to-use software and currently a leading industrial plasma
simulation tool.

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| www.esgeetech.com| VizGlow version 1.8 (Feb 2012)For further information on this application note or details about the VizGlow and othersoftware packages you may contact us atEsgee Technologies Inc.
14, North PeakAustin, Texas 78746, USA
info@esgeetech.com
www.esgeetech.com

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