Etching Simulation is the TCAD computational modeling of material removal processes — including wet chemical etching, reactive ion etching (RIE), atomic layer etching (ALE), and ion beam etching — predicting three-dimensional profile evolution, critical dimension (CD) changes, sidewall angles, selectivity, microloading effects, and aspect-ratio dependent etch rates that determine whether patterned features meet design specifications after the etch process.
What Is Etching Simulation?
Etching shapes the three-dimensional structure of semiconductor devices by selectively removing material. Simulation traces how the material surface evolves during removal, capturing the complex interplay between chemistry, physics, and geometry:
Geometric (String/Level Set) Models
Fast profile evolution simulation treating the etch as a surface moving at a specified velocity normal to the local surface. The level set method represents the surface as the zero-contour of a signed distance function, allowing complex topology changes (holes merging, features separating) without numerical instability. Used for macro-scale profile shape prediction when detailed atomic chemistry is not needed — efficient enough for full-wafer pattern density calculations.
Monte Carlo Physical Models
Simulate individual ion and radical trajectories as they strike the surface, modeling:
- Ion Bombardment: Directional ions from the plasma break chemical bonds and physically sputter material.
- Radical Reactions: Chemically reactive neutral species adsorb on the surface, react with the material, and form volatile byproducts that desorb.
- Ion-Enhanced Chemistry: The combination of ion bombardment and radical chemistry provides etch rates typically 10–100× higher than either alone, enabling anisotropic (directional) etching at the feature scale.
Why Etching Simulation Matters
- Profile Control for Advanced Nodes: FinFET fins require near-vertical (>85°) sidewalls — even 1° deviation changes the fin width by 0.2 nm at 5 nm geometry. Nanosheet FET release etches require removing SiGe sacrificial layers with angstrom-level uniformity around the Si nanosheet. Simulation guides plasma chemistry and bias power selection to achieve target profiles.
- RIE Lag / Aspect Ratio Dependent Etching (ARDE): Contact holes and trenches etch more slowly than open field areas due to ion flux shadowing and neutral depletion at the bottom of high-aspect-ratio features. Deep trenches for DRAM capacitors or through-silicon vias require simulation to predict how etch rates change with depth and to design etch recipes that compensate for lag.
- Selectivity Modeling: Every etch must stop at the correct material interface — etching silicon over a silicon nitride stop layer requires high Si:SiN selectivity. Simulation predicts when the etch will punch through the stop layer due to non-uniformity, guiding the etch endpoint detection strategy.
- Microloading and Pattern Density Effects: Dense arrays of features etch differently from isolated features due to local radical depletion and byproduct redeposition. Simulation quantifies these loading effects, enabling layout-level corrections or process adjustments.
- ALE Cycle Optimization: Atomic Layer Etching uses alternating cycles of surface modification and removal to achieve angstrom-per-cycle precision without ion damage. Simulation predicts the saturation behavior of each half-cycle, guiding pulse timing and chemistry selection.
Tools
- Synopsys Sentaurus Topography (formerly Topo3D): Industry-standard 3D etch and deposition simulation with Monte Carlo physical models.
- Silvaco Victory Topography: 3D profile simulation for complex etch and deposition processes.
- SRIM/TRIM: Ion range and damage simulation (primarily for ion beam etching and implantation).
Etching Simulation is virtual material sculpting — mathematically tracing how plasma chemistry and ion bombardment carve three-dimensional device structures from stacked material layers, predicting the profile, dimension accuracy, and process window before wafer fabrication to avoid the costly iteration cycles that would otherwise be required to optimize complex multi-step etch processes.