process window analysis

**Process Window Analysis** is the **systematic evaluation of the focus and exposure dose range within which patterned features meet their CD specification** — determining the overlapping process window where ALL features on a mask simultaneously satisfy their dimensional requirements. **Process Window Construction** - **FEM Data**: Measure CD vs. focus and dose from a Focus-Exposure Matrix wafer. - **CD Limits**: Define upper and lower CD specification limits (e.g., target ± 10%). - **Contour Plot**: Plot the region in focus-dose space where CD is within specs — the process window. - **Window Metrics**: Depth of Focus (DOF) = focus range; Exposure Latitude (EL) = dose range (as % of nominal). **Why It Matters** - **Manufacturability**: A large process window (large DOF × large EL) indicates robust manufacturability. - **Overlap**: In practice, multiple features must all be within spec simultaneously — the overlapping process window. - **Margin**: Process window analysis determines the margin for process variation — how much focus and dose can drift. **Process Window Analysis** is **finding the sweet spot** — determining the focus and dose range where all critical features simultaneously meet specifications.