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.