Mask Inspection is the process of detecting defects on photomasks using high-resolution imaging and comparison algorithms — scanning the entire mask pattern at high resolution and comparing it to the design database (die-to-database) or to adjacent identical dies (die-to-die) to find any deviations.

Inspection Modes

• Die-to-Database: Compare the mask image to the design layout — detects any deviation from the intended pattern.
• Die-to-Die: Compare identical dies on the mask — defects appear as differences between dies.
• Reflected/Transmitted: Inspect using reflected light (for EUV masks) or transmitted light (for DUV transmissive masks).
• Wavelength: DUV inspection wavelengths (193nm, 248nm) for highest resolution — actinic (EUV) inspection for EUV masks.

Why It Matters

• Zero Tolerance: A single undetected mask defect prints on every wafer — mask inspection must have near-perfect sensitivity.
• Sensitivity: Must detect defects small enough to print — sensitivity requirements tighten with each technology node.
• Cost: Inspection is a significant fraction of the total mask manufacturing time and cost.

Mask Inspection is finding the needle in the mask — high-resolution scanning and comparison to detect every printable defect on the photomask.