opc model calibration

**OPC Model Calibration** is the **process of fitting the optical and resist models used in OPC simulation to match actual patterning results** — measuring CD, profile, and defectivity on calibration wafers and adjusting model parameters until the simulation matches the measured silicon data. **Calibration Process** - **Test Mask**: A calibration mask with diverse feature types — dense/isolated lines, contacts, line ends, tips, at multiple pitches and CDs. - **Wafer Data**: Process FEM wafers with the test mask — measure CD at many sites across the focus-dose matrix. - **Model Fitting**: Adjust optical parameters (aberrations, flare, polarization) and resist parameters (diffusion, threshold, acid/base) to minimize CD error. - **Validation**: Validate on a separate set of features not used in calibration — cross-validation of model accuracy. **Why It Matters** - **OPC Accuracy**: The OPC model determines the quality of all OPC corrections — a poorly calibrated model produces incorrect masks. - **RMS Error**: State-of-art calibration achieves <1nm RMS CD error — matching simulation to silicon. - **Recalibration**: Model recalibration is needed when process conditions change (new resist, different etch, new scanner). **OPC Model Calibration** is **teaching the simulator to match reality** — fitting lithography models to measured data for accurate OPC and process simulation.