apc (advanced process control)

APC (Advanced Process Control) uses real-time metrology feedback to automatically adjust process recipes, maintaining tighter process control than manual adjustments. **Feedback control**: Post-process metrology results used to adjust recipe for next lot. Example: if post-etch CD is 1nm above target, reduce litho dose for next lot. **Feed-forward control**: Pre-process measurements used to adjust current process. Example: incoming film thickness measured, etch time adjusted to compensate. **R2R control**: Run-to-Run controller calculates recipe adjustments between lots using EWMA (Exponentially Weighted Moving Average) or model-based algorithms. **Control loop**: Measure -> Compare to target -> Calculate correction -> Apply to recipe -> Measure again. Continuous optimization. **Controlled parameters**: Litho dose and focus, etch time and power, CMP pressure and time, CVD temperature and time, implant dose. **Models**: Linear or nonlinear models relate recipe parameters to output metrics. Models updated with ongoing data. **EWMA**: Exponentially Weighted Moving Average filters measurement noise while tracking process drift. Most common R2R algorithm. **Multi-input multi-output (MIMO)**: Advanced APC controls multiple outputs simultaneously by adjusting multiple recipe parameters. **Benefits**: Tighter CD control, better uniformity, higher yield, reduced operator intervention, faster response to process drift. **Integration**: APC systems interface with tool controllers, metrology tools, and MES through SECS/GEM or EDA interfaces. **Vendors**: Onto Innovation (Angstrom), Rudolph/Onto, Applied Materials (iAPC), proprietary fab-developed systems.