Define the Mask to Wafer Working Gap

# Define the Mask-to-Wafer Working Gap

Removing physical contact meant introducing a deliberate working gap between the mask and the wafer, with an optical system filling that gap and doing the job contact once did directly.

That gap had to be held to a known, repeatable distance across the exposure field, because any variation changed how accurately the projected image landed on the wafer.

Holding this gap stable and consistent, rather than letting the mask simply rest on the wafer, was itself a precision mechanical and optical engineering problem that a usable projection system had to solve.

THE WORKING GAPOld approachzero gap, mask resting on the waferNew approacha controlled, known gap, filled by projection opticsRequirementthe gap must stay stable across the whole exposure field

Diagram above: the working gap.

WHY GAP CONTROL MATTEREDImage accuracygap variation shifts where the pattern landsMechanical demandthe system had to hold this gap preciselyPayoffa controlled gap enabled, rather than prevented, non-contact exposure

Diagram above: why gap control mattered.

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