VizGlow Application Note
Simulation of a Capacitively Coupled Plasma (CCP) Reactor Used in
Semiconductor Materials Processing

Capacitively Coupled Plasma (CCP)
discharges
inparallel-plate
configuration are commonly used insemiconductor and other materials
processing applications.
Thesedischarges provide a compact platform
in which a plasma can be generated toprocess a flat wafer surface. The
highly directional ion impact at thewafer surface with high ion impact
energies is beneficial to a number ofwafer processes; in particular for etchprocesses.
This application note
discusses the simulation of a typical
CCP reactor used in the semiconductor
process industry. The VizGlow Plasma
Modeling Software Package is used.

(a) CCP reactor geometry(b) Mesh for CCP reactor
Figure 1: Geometry and mesh for Capacitively Coupled
Plasma (CCP) reactor.

The geometry and computationalmesh for this problem is shown in Fig.
1. The mesh contains about 21,000 cells, and is divided into 6 physical subdomains. The
geometry includes a gas subdomain where the plasma is formed, a top grounded electrode, abottom powered electrode that holds a wafer, a top dielectric that isolated the top electrodefrom the grounded reactor wall, a bottom dielectric that isolates the bottom powered
electrode from the reactor walls, and a focus ring that defines the edge geometry for the wafer
and the powered electrode. The mesh comprises a mix of quadrilateral and triangular cells indomain. Specifically the plasma (gas) subdomain is meshed with quadrilateral cells that have
non-uniform resolution to capture the sheaths at wall and wafer boundaries accurately.
The wafer has a standard 300 mm dia. The wafer is assumed to be made of silicon, thedielectrics are made of alumina, and the focus ring is made of quartz. The powered electrode isdriven by a 100 MHz excitation frequency that delivers 300 W radio-frequency (RF) power toCopyright © Esgee Technologies Inc.

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the plasma. A pure argon gas at 50mTorr pressure is assumed. Theplasma gas phase chemistry isrepresented by 4 species (electrons E,argon ions Ar+, argon metastables Ar*,argon neutrals Ar).
The plasma
chemistry comprises 6 reaction
including electron impact excitationand direct ionization, stepwise
ionization, Penning ionization, andFigure 2: Cycle-averaged electron temperature in themetastablequenching.
TheCCP reactor.
simulations are run to a periodic
steady state. The VizGlow Plasma Modeling Software Package is used in self-consistent mode tosolve for the CCP plasma phenomena. These simulations are performed without including
electromagnetic (EM) wave effects that are known to redistribute power deposition in thereactor. The effect of EM wave will
be discussed in another application
note.
Figure 2 shows a cycle-averaged
electron temperature in the reactor.
The electron temperature is nearly
uniform in most of the reactor
volume with a value of about
20,000 K (~2 eV). In the vicinity ofthe powered electrode/wafer theFigure 3: Cycle-averaged electron density profile in the
averaged electron temperature isCCP reactor.
about 150,000 K (~ 15 eV). The
electron temperature is non-uniform along the radial length of the wafer and peak near theradial edge of the wafer.

Figure 4: Argon metastable species density profiles inthe CCP reactor.

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|Figure 3 shows the cycle-averaged
electron density profile in the reactor.
The electron densities are seen to bequite non-uniform with a wafer edge
peak profile that corresponds to thedominant edge power deposition
resulting for wafer edge electrostatic
field focusing. Peak electron densitiesof ~ 3x1016 m-3 are seen. The argon ion
densities correspond closely to electron
density profiles.

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Figure 4 shows the argon metastable species density profiles in the reactor. An off-axis
metastable density peak at a similar radial location to the electron density peak is seen. The
metastable densities are however peaked close to the wafer surface close to the regions where
the electron temperatures are high.
Figure 5 shows the ion energy
distribution function (IEDF) for ion impact
at two locations on the wafer surface. The
IEDF
information
isgenerated
automatically by VizGlow and is a usefulmetric for process behavior at the wafer
surface. IEDFs for the wafer center andedge are shown. Ions impact the wafer
surface with a range of energies depending
Figure 5: Ion energy distribution function (IEDF)
on the excitation frequencies, mass of ions,for
AR+ ions at the center and edge of the wafer.
and the sheath thickness. A classical bimodal IEDF is seen. For the reactor
condition used in these simulations, the lowest ion impact energies are between 15 and 20 eV
and the highest are between 30 to 35 eV. The IEDF width is nearly the same for both the wafer
center and edge locations. The wafer edge IEDF is shifted to a slightly higher energy comparedto the wafer center.
Finally we provide a note on the numerical convergence of the simulations. CCP simulations
can be time consuming and the best judgment for simulation convergence is provided byplacing trace points several locations in thesimulation domain and tracking the time evolutionof various important plasma properties. For
example Fig. 6 shows the time evolution ofelectron and ion species densities and the argon
metastable species density at the reactor centerline (axis) mid-gap between the electrodes.
Although the simulation was run 100
microseconds of simulated physical time, the timeevolution of the species densities indicates that anumerically converged solution is obtained inabout 40 microseconds.
Figure 6: Time evolution of electron (E),argon ion (AR+) and argon metastable(AR*) species densities at a trace point in
the plasma volume. The time evolution ofvarious species and plasma parameters attrace points are used to judge numericalconvergence in the simulation.

Copyright © Esgee Technologies Inc.

|In summary, the VizGlow Plasma Modeling
Software Package provide a wide range of physicalmodels and options that allows one to simulate
complexcoupledphenomena
thatareencountered in most plasma discharges. TheVizGlow Plasma Modeling Software Package iswww.esgeetech.com| VizGlow version 1.8 (Feb 2012)

part 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.
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

Copyright © Esgee Technologies Inc.

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www.esgeetech.com| VizGlow version 1.8 (Feb 2012)