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add oxidation model to documentation
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‎docs/examples/index.md‎

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* [GDS Reader](https://github.com/ViennaTools/ViennaPS/tree/master/examples/GDSReader)
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* [Interpolation Demo](https://github.com/ViennaTools/ViennaPS/tree/master/examples/interpolationDemo)
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* [Oxide Regrowth](https://github.com/ViennaTools/ViennaPS/tree/master/examples/oxideRegrowth)
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* [Step Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/stepOxidation)
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* [Fin Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/finOxidation)
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* [Trench Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/trenchOxidation)
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* [LOCOS Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/locosOxidation)
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* [SiGe Selective Etching](https://github.com/ViennaTools/ViennaPS/tree/master/examples/SiGeSelectiveEtching)
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* [Trench Deposition Geometric](https://github.com/ViennaTools/ViennaPS/tree/master/examples/trenchDepositionGeometric)
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* [Trench Deposition Geometric](https://github.com/ViennaTools/ViennaPS/tree/master/examples/trenchDepositionGeometric)

‎docs/models/prebuilt/index.md‎

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* [Selective Epitaxy]({% link models/prebuilt/selectiveEpitaxy.md %})
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* [Geometric Models]({% link models/prebuilt/geometric.md %})
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* [Oxide Regrowth]({% link models/prebuilt/oxideRegrowth.md %})
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* [Thermal Oxidation]({% link models/prebuilt/oxidation.md %})
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## Exposed Models With Example Coverage
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‎docs/models/prebuilt/oxidation.md‎

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---
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layout: default
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title: Thermal Oxidation
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parent: Pre-Built Models
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grand_parent: Process Models
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nav_order: 14
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---
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# Thermal Oxidation
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{: .fs-9 .fw-500}
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```c++
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#include <psOxidation.hpp>
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```
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---
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`Oxidation` models thermal silicon oxidation using the coupled oxidation solver
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provided by ViennaLS. The model exposes process-level controls such as furnace
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temperature, oxidation time, oxidant species, pressure, and crystal orientation,
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while the underlying solver handles oxidant diffusion, interface motion, and
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oxide deformation.
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Unlike most particle- or velocity-field-based process models, `Oxidation`
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manages its own physics. It is applied through the normal `Process` interface,
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but the model internally performs the required coupled diffusion and deformation
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steps.
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## Physical Model
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The built-in rate constants follow a Deal-Grove style thermal oxidation model.
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The model supports dry oxidation (`O2`) and wet oxidation (`H2O`) and includes
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crystal-orientation-dependent reaction-rate corrections for silicon.
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During each internal time step, the solver computes:
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* oxidant diffusion through the oxide,
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* reaction at the Si/SiO2 interface,
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* oxide volume expansion,
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* deformation and pressure inside the oxide, and
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* stress feedback on diffusion and reaction rates.
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If a Si3N4 mask is present in the material stack, the model activates LOCOS
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physics. In that mode, oxidant transport below the nitride mask, mask bending,
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and constrained oxide expansion produce the characteristic bird's-beak shape.
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## Domain Requirements
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The domain must contain a silicon material level set, typically `Material::Si`
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or `Material::BulkSi`. If no SiO2 level set is present, the model can create a
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thin native oxide seed internally.
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Common material roles are:
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| Role | Default material |
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|------|------------------|
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| Silicon | `Material::Si` |
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| Oxide | `Material::SiO2` |
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| LOCOS mask | `Material::Si3N4` |
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The material roles can be overridden with `setSiliconMaterial`,
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`setOxideMaterial`, and `setMaskMaterial`.
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## Main Parameters
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| Method | Description |
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|--------|-------------|
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| `setTemperature(temperatureC)` | Furnace temperature in degrees Celsius. |
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| `setTime(timeHr)` | Total oxidation time in hours. |
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| `setOxidant(oxidant)` | Oxidant species: `OxidantType::Dry` or `OxidantType::Wet`. |
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| `setPressure(pressureAtm)` | Ambient pressure in atm; scales both linear and parabolic rates. |
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| `setOrientation(orientation)` | Silicon orientation: `Si100`, `Si110`, `Si111`, or `PolySi`. |
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| `setTimeStep(dtHr)` | Optional maximum internal time step in hours. The actual step remains CFL-limited. |
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| `setCFLFactor(factor)` | CFL factor for internal interface motion, clamped below 0.5. |
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| `setInitialOxideThickness(thicknessUm)` | Native oxide seed thickness in micrometers if no oxide layer exists. |
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| `setTransferCoefficient(coefficient)` | Gas-transfer coefficient at the oxide/ambient interface. |
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| `setMaxGridPoints(maxGridPoints)` | Caps the Cartesian grid size used by the ViennaLS solves. |
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## Stress and Solver Controls
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| Method | Description |
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|--------|-------------|
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| `setReactionActivationVolume(volume)` | Stress coupling for the interface reaction rate. |
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| `setDiffusionActivationVolume(volume)` | Stress coupling for oxide diffusivity. |
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| `setCouplingIterations(iterations)` | Maximum outer diffusion-deformation coupling iterations. |
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| `setCouplingTolerance(tolerance)` | Convergence tolerance for the outer coupling loop. |
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| `setMechanicsIterations(iterations)` | Maximum oxide mechanics iterations. |
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| `setPressureIterations(iterations)` | Maximum pressure-solve iterations. |
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| `setStokesIterations(iterations)` | Maximum Stokes velocity iterations. |
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| `setPressureTolerance(tolerance)` | Pressure-solve tolerance. |
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| `setStokesTolerance(tolerance)` | Stokes-solve tolerance. |
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| `setMechanicsTolerance(tolerance)` | Mechanics coupling tolerance. |
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| `setSimpleVelocityRelaxation(alpha)` | SIMPLE velocity relaxation factor. |
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| `setSimplePressureRelaxation(beta)` | SIMPLE pressure relaxation factor. |
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| `setSolveBounds(minIndex, maxIndex)` | Restricts the solve to explicit Cartesian index bounds. |
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| `clearSolveBounds()` | Clears explicit solve bounds. |
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## LOCOS Mask Controls
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These controls are used when the domain contains the configured mask material,
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by default `Material::Si3N4`.
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| Method | Description |
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|--------|-------------|
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| `setMaskMaterial(material)` | Selects the material treated as the oxidation mask. |
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| `setMaskParameters(params)` | Replaces the full ViennaLS mask parameter object. |
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| `setMaskTractionIterations(iterations)` | Maximum mask-traction iterations. |
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| `setMaskTractionTolerance(tolerance)` | Mask-traction convergence tolerance. |
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| `setMaskTractionRelaxation(relaxation)` | Outer mask-traction relaxation factor. |
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| `setMaskContactLoadRelaxation(relaxation)` | Contact-load relaxation factor. |
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| `setMaskContactReleaseFraction(fraction)` | Fraction used for contact release. |
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| `setMaskUnilateralContact(enabled)` | Enables or disables unilateral contact. |
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| `setMaskSmootherOmega(omega)` | Multigrid smoother over-relaxation for mask mechanics. |
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| `setMaskBendingBounds(minIndex, maxIndex)` | Restricts mask bending to explicit bounds. |
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| `clearMaskBendingBounds()` | Clears explicit mask bending bounds. |
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| `setMaskCouplingIterations(iterations)` | Maximum mask/deformation coupling iterations. |
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| `setMaskCouplingTolerance(tolerance)` | Mask/deformation coupling tolerance. |
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## GPU Controls
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The default solver mode is CPU. GPU acceleration is available when ViennaLS was
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built with GPU support.
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| Method | Description |
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|--------|-------------|
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| `setGpuMode(mode)` | Selects `GpuMode::Cpu` or `GpuMode::Gpu`. |
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| `setGpuPreconditioner(preconditioner)` | Selects the GPU BiCGSTAB preconditioner, such as Jacobi or ILU0. |
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## Output Helpers
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| Method | Description |
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|--------|-------------|
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| `estimatePlanarOxideThickness(initialOxideThickness)` | Returns the planar Deal-Grove oxide thickness estimate for the current settings. |
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| `saveSurfaceMesh(domain, fileName)` | Writes a wrapped surface mesh without mutating the active simulation state. |
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| `saveVolumeMesh(domain, baseName)` | Writes a wrapped volume mesh and associated oxide-field output. |
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## Example Usage
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<details markdown="1">
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<summary markdown="1">
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C++
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{: .label .label-blue}
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</summary>
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```c++
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using namespace viennaps;
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auto model = SmartPointer<Oxidation<double, 2>>::New();
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model->setTemperature(1000.0);
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model->setTime(0.2);
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model->setOxidant(OxidantType::Wet);
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model->setPressure(1.0);
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model->setOrientation(SiliconOrientation::Si100);
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model->setMaxGridPoints(5000000);
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Process<double, 2>(domain, model).apply();
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```
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</details>
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<details markdown="1">
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<summary markdown="1">
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Python
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{: .label .label-green}
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</summary>
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```python
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import viennaps as vps
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model = vps.Oxidation()
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model.setTemperature(1000.0)
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model.setTime(0.2)
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model.setOxidant(vps.OxidantType.Wet)
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model.setPressure(1.0)
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model.setOrientation(vps.SiliconOrientation.Si100)
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model.setMaxGridPoints(5_000_000)
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vps.Process(domain, model).apply()
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```
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</details>
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## Practical Notes
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* Use smaller `gridDelta` values for production results, but keep in mind that
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the diffusion/deformation grid scales strongly with dimension.
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* `setTimeStep` is an upper bound. The accepted internal step is still limited
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by the CFL condition.
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* LOCOS simulations need enough vertical space above the mask and oxide so that
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the growing oxide and bent mask are not clipped by the domain bounds.
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* In narrow or confined geometries, stress feedback can strongly reduce the
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local reaction rate. Inspect pressure and stress fields in the oxide-field
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output to understand growth suppression.
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## Related Examples
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* [Step Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/stepOxidation)
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* [Fin Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/finOxidation)
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* [Trench Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/trenchOxidation)
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* [LOCOS Oxidation](https://github.com/ViennaTools/ViennaPS/tree/master/examples/locosOxidation)

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