wafer-to-wafer control

**Wafer-to-Wafer (W2W) Control** is a **run-to-run control strategy that adjusts process parameters between individual wafers** — providing finer control granularity than lot-to-lot R2R control by accounting for within-lot variability such as slot position effects. **How Does W2W Control Work?** - **Per-Wafer Measurement**: Measure the critical output for each wafer (not just lot averages). - **Per-Wafer Update**: Apply EWMA or model-based correction to adjust the recipe for the next wafer. - **Slot-Dependent Effects**: Compensate for known slot-to-slot variations in batch processes (furnace position effects). - **Threading**: Controller state is maintained per-chamber for multi-chamber tools. **Why It Matters** - **Within-Lot Uniformity**: Reduces wafer-to-wafer variation within a lot (not addressed by lot-to-lot R2R). - **Single-Wafer Tools**: Natural control granularity for single-wafer process tools (etch, CVD, PVD). - **Tighter Specs**: Advanced nodes require tighter within-lot variation, making W2W control increasingly necessary. **W2W Control** is **individual wafer tuning** — adjusting the recipe for each wafer instead of each lot for tighter process control.