Fin Patterning and Sidewall Transfer (3D)

This tutorial demonstrates a simple 3D process flow using ViennaPS:

  1. Create a simulation domain
  2. Add a mask feature (fin)
  3. Perform isotropic deposition
  4. Perform directional etching
  5. Strip the mask
  6. Transfer the pattern into the substrate

The example mimics a simplified sidewall transfer process.

Download Jupyter Notebook: 06_emulation.ipynb

1. Import ViennaPS and Set Dimension 

import viennaps as ps 
ps.setDimension(3)

ViennaPS supports 2D and 3D simulations. Here we explicitly set the simulation to 3D.

2. Create the Simulation Domain 

extent = 30
gridDelta = 0.3

domain = ps.Domain(
    xExtent=extent,
    yExtent=extent,
    gridDelta=gridDelta,
    boundary=ps.BoundaryType.REFLECTIVE_BOUNDARY
)

Parameters

  • xExtent, yExtent: Lateral size of the simulation window
  • gridDelta: Grid spacing (controls resolution)
  • boundary: Reflective boundaries prevent material from leaving the domain

This creates a square domain of size 30 × 30 units with a resolution of 0.3 units.

3. Create a Fin Mask Structure

We now add a rectangular fin structure that acts as a mask.

ps.MakeFin(
    domain,
    finWidth=6.,
    finHeight=0.,
    maskHeight=10.0
).apply()

Parameters

  • finWidth = 6 → width of the feature
  • finHeight = 0 → no substrate protrusion (mask only)
  • maskHeight = 10 → height of the resist layer

This creates a vertical resist structure on top of the substrate.

4. Save and Visualize the Initial Geometry 

domain.saveSurfaceMesh("emulation_1", addInterfaces=True)
domain.show()
  • saveSurfaceMesh() exports the current geometry
  • addInterfaces=True includes material interfaces
  • show() opens the built-in viewer

At this stage, only the mask structure is present.

5. Isotropic Deposition (Conformal Coating)

Next, we deposit a conformal SiO₂ layer.

Duplicate the Top Level Set 

domain.duplicateTopLevelSet(ps.Material.SiO2)

This creates a new material layer (SiO₂) on top of the existing geometry.

Apply Isotropic Deposition 

isoDepo = ps.IsotropicProcess(rate=1.0)
ps.Process(domain, isoDepo, 4.0).apply()

Explanation

  • rate = 1.0 → constant deposition rate
  • time = 4.0 → process duration

Since the process is isotropic, deposition occurs uniformly in all directions. This produces a conformal coating over the mask and substrate.

domain.show()

You should now see a conformal SiO₂ layer.

6. Directional Etch (Top Removal)

Now we remove the horizontal parts of the deposited layer.

directionalEtch = ps.DirectionalProcess(
    direction=[0., 0., 1.],
    directionalVelocity=1.0,
    isotropicVelocity=0.0,
    maskMaterial=ps.Material.Undefined,
    calculateVisibility=False
)

ps.Process(domain, directionalEtch, 5.0).apply()

Parameters

  • direction=[0,0,1] → etch in vertical direction
  • directionalVelocity=1.0 → pure anisotropic etch
  • isotropicVelocity=0.0 → no lateral component
  • calculateVisibility=False → no shadowing

This step removes the horizontal SiO₂ but leaves material on the sidewalls.

domain.show()

You should now observe SiO₂ spacers along the mask sidewalls.

7. Remove the Original Mask 

domain.removeMaterial(ps.Material.Mask)

This simulates resist stripping. Only the SiO₂ sidewall spacers remain.

8. Final Directional Etch (Pattern Transfer)

We now etch the substrate using the SiO₂ spacers as a hard mask.

directionalEtch = ps.DirectionalProcess(
    direction=[0., 0., 1.],
    directionalVelocity=1.0,
    isotropicVelocity=0.0,
    maskMaterial=ps.Material.SiO2,
    calculateVisibility=False
)

ps.Process(domain, directionalEtch, 20.0).apply()

Key Difference

  • maskMaterial=ps.Material.SiO2

This means the SiO₂ spacers are protected and act as a hard mask.

After 20 time units, the substrate is etched vertically beneath the spacers.

domain.saveVolumeMesh("emulation_5")
domain.show()

The final structure represents a transferred fin pattern defined by the spacer width.

Download Jupyter Notebook: 06_emulation.ipynb