Plasma and Magnetic Fields
1
In the Model Builder window, under Component 1 click on the Plasma node.
2
In the settings window, Locate the Plasma Properties section and select the Use reduced electron transport properties checkbox.
3
Click on the Selection List window. Select Domain 3 only.
4
In the Model Builder window, right-click Plasma and choose Cross Section Import.
5
In the Cross Section Import settings window, locate the Cross Section Import section.
6
Click the Browse button.
7
Browse to the module Application Library folder and double-click the file Ar_xsecs.txt.
Now you add two more regular reactions which describe how electronically excited argon atoms are consumed on the volumetric level. The rate coefficients for these reactions are taken from the literature.
1
In the Model Builder window, right-click Plasma and choose the domain setting Heavy Species Transport > Reaction .
2
In the Reaction settings window, locate the Reaction Formula section.
3
In the Formula field, type Ars+Ars=>e+Ar+Ar+. Click off the settings window.
4
Locate the Kinetics Expressions section. In the kf field, type 3.734E8.
5
In the Model Builder window, right-click Plasma and choose the domain setting Heavy Species Transport > Reaction .
6
In the Reaction settings window, locate the Reaction Formula section.
7
In the Formula field, type Ars+Ar=>Ar+Ar. Click off the settings window.
8
Locate the Kinetics Expressions section. In the kf field, type 1807.
When solving any type of reacting flow problem there always needs to be one species which is selected to fulfill the mass constraint. This should be taken as the species with the largest mass fraction.
1
In the Model Builder window, under Component 1 > Plasma click Species: Ar .
2
In the Species settings window, locate the Species Formula section.
3
Select the From mass constraint checkbox.
When solving a plasma problem the plasma must be initially charge neutral. COMSOL automatically computes the initial concentration of a selected ionic species such that the initial electroneutrality constraint is satisfied. Once the simulation begins to time step, the plasma need not be charge neutral. In fact, the separation of space charge between the ions and electrons close to the wall is a critical component in sustaining the discharge.
1
In the Model Builder window, under Component 1 > Plasma click Species: Ar+ .
2
In the Species settings window, locate the Species Formula section.
3
Select the Initial value from electroneutrality constraint checkbox.
Initial conditions for the electron number density and mean electron energy are critical for any plasma model. If the initial electron density is too low then the plasma may not be able to sustain itself and may self-extinguish. If the initial electron density is too high then convergence problems may occur during initial time steps.
1
In the Model Builder window, under Component 1 > Plasma click Initial Values 1 .
2
In the Initial Values settings window, locate the Initial Values section.
3
In the ne,0 field, type 1E15[1/m^3].
4
In the ε0 field, type 5[V].
5
In the Model Builder window, under Component 1 > Plasma click Plasma Model 1 .
6
In the Plasma Model settings window, locate the Model Inputs section.
7
In the T field, type T0.
8
In the pA field, type p0.
9
Locate the Electron Density and Energy section. In the μeNn field, type mueN.
Surface reactions must always be included in a plasma model since they describe how ionic, excited, and radical species interact with the wall.
1
In the Model Builder window, under Component 1 right-click Plasma and choose the boundary condition Heavy Species Transport > Surface Reaction .
2
In the Surface Reaction settings window, locate the Reaction Formula section.
3
In the Formula field, type Ars=>Ar.
4
Locate the Boundary Selection section. From the Selection list, choose Walls.
5
In the Model Builder window, right-click Plasma and choose the boundary condition Heavy Species Transport > Surface Reaction .
6
In the Surface Reaction settings window, locate the Reaction Formula section.
7
In the Formula field, type Ar+=>Ar.
8
Locate the Boundary Selection section. From the Selection list, choose Walls.
Now add boundary conditions to describe how the electrons interact with the wall and specify that the walls are grounded.
1
In the Model Builder window, right-click Plasma and choose the boundary condition Drift Diffusion > Wall .
2
In the Wall settings window, locate the General Wall Settings section.
3
In the re field, type 0.2.
4
Locate the Boundary Selection section. From the Selection list, choose Walls.
5
In the Physics toolbar, click Boundaries and choose Ground .
6
In the Ground settings window, locate the Boundary Selection section.
7
From the Selection list, choose Walls.
You need to compute the AC electric field both inside and outside the plasma. It is not necessary to compute the high frequency fields in the wafer or wafer pedestal, so start by modifying the selection for the Magnetic Fields interface.
1
In the Model Builder window, click Magnetic Fields.
2
Select Domains 3–6 and 8–12 only.
The Coil feature allows you to drive the system with a fixed total power. Some of this power will be dissipated in the coil, the rest will be coupled into the plasma. In this example 1500 W are applied to the system. This results in a plasma with a high number density. You also need to specify the gas temperature and pressure.
1
In the Model Builder window, right-click Magnetic Fields and choose the domain setting Coil .
2
In the Coil settings window, locate the Domain Selection section.
3
From the Selection list, choose Coils.
4
Locate the Coil section. Select the Coil group checkbox.
In the Coil excitation, select Power and in the Pcoil field, type Psp.