Tutorials Manual

Chapter 4: Materials Problems
Tutorials Manual
4.3.3 Fluorocarbon Plasma Etching of Silicon Dioxide
4.3.3.1 Project Description
This user tutorial is an example of modeling a low-pressure plasma reactor as a
steady-state Perfectly Stirred Reactor, using the fluorocarbon plasma chemistry set
described in Section 4.4.6. This example is representative of a high-density plasma,
with a plasma power of 3000 Watts and a pressure of 10 mtorr. Pure
hexafluoroethane is the inlet gas. The energy equation and the electron energy
equation are solved, and a heat-transfer correlation is used to account for heat loss
through the wall of the reactor. This example illustrates the use of multiple materials,
each with a different set of surface reactions, as well as the use of continuations with
varying flow rate and ion impact energy.
4.3.3.2 Project Setup
The project file is called plasma_psr__c2f6_etch.ckprj. The data files used for this
sample are located in the samples\plasma_psr__c2f6_etch directory. This reactor
diagram contains a gas inlet and a plasma PSR.
The reactant gas mixture, which is pure C 2 F 6 in this case, is input on the Speciesspecific
Property tab of the C1_Inlet1 panel. The gas flow rate (30 sccm), inlet gas
temperature and inlet electron temperature are input on the Stream Property tab of
the R1_IN1 panel. The latter is required, but has little impact on the solution unless
there are electrons in the input gas mixture.
The C1_ Plasma PSR panel is where most of the parameters are input. The Reactor
Physical Property tab allows selection of problem type, as well as places to enter
parameters such as the plasma power, pressure (10 mTorr), volume, internal area,
heat loss parameters, cross-section for electron momentum loss, and initial guesses
for the electron, neutral, and ion temperatures. The Species-specific Data tab allows
input of initial guesses for the steady-state gas composition, surface site fractions,
and bulk activities, on the corresponding sub-tabs, as well as species-specific values
for electron-momentum loss cross-sections. A good initial guess for the gas and
surface compositions (one that is close to the steady-state solution) will result in fast
convergence, while a poor initial guess can lead to failure of the simulation. The Bulkphase
-specific Data tab is used to indicate that all the bulk materials are being
etched, which affects some of the equations. The Material-specific Properties tab is
for specifying properties like surface temperature (if different from the neutral gas
temperature), ion energy or bias power, Bohm factor, sheath energy loss factor, area
fraction, or heat loss, either for all materials, or on a per-material basis. For this nonparameter-study
problem, the bottom part of the panel is used to set up values that
are dependent on the material. Material-independent properties can be set on the
RD0411-C20-000-001 149 © 2007 Reaction Design