overlapping process window

**Overlapping Process Window** is the **intersection of individual process windows for all critical features on a mask** — the focus-dose operating range where dense lines, isolated lines, contacts, and all other critical patterns simultaneously meet their CD specifications. **Overlapping Window Construction** - **Individual Windows**: Each feature type (dense, isolated, contacts) has its own process window in focus-dose space. - **Intersection**: The overlapping window is the geometric intersection of all individual windows. - **Limiting Feature**: The feature with the smallest individual window limits the overall overlapping window. - **Center**: The optimal operating point is the center of the overlapping window — maximum margin in all directions. **Why It Matters** - **Real Manufacturing**: All features must work simultaneously — a process that works for dense lines but fails on contacts is useless. - **OPC**: Optical Proximity Correction adjusts patterns to maximize the overlapping process window. - **Mask Optimization**: Sub-resolution assist features (SRAF) and mask bias are tuned to center the overlapping window. **Overlapping Process Window** is **where everything works together** — the shared focus-dose space where all critical features simultaneously meet their requirements.