Stepper & Scanner Basics

How exposure tools work — step-and-repeat vs step-and-scan

How Lithography Tools Work

Lithography exposure tools project a circuit pattern from a reticle (mask) onto the wafer through a precision optical system:

Stepper (step-and-repeat): Exposes one die field at a time, then steps to the next position. Older technology, simpler but lower throughput.
Scanner (step-and-scan): Both the reticle and wafer move simultaneously during exposure — the reticle scans through a narrow slit of illumination. This allows a larger exposure field while keeping the optics compact. All modern tools are scanners.

Key performance metrics:

Resolution: Minimum feature size (determined by wavelength and NA)
Overlay: Alignment accuracy between successive layers (< 2 nm for advanced nodes)
Throughput: Wafers per hour (150–300+ WPH depending on tool and process)
Focus uniformity: Depth of focus across the exposure field (critical for yield)

Key Concept: The Wafer Stage

The wafer stage positions the wafer with sub-nanometer precision while moving at speeds up to 500 mm/s. It uses laser interferometry for position measurement and magnetic levitation for vibration isolation. This is one of the most precise mechanical systems ever built.

Epitaxy Systems

DUV Systems

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What is the key difference between a stepper and a scanner?

A scanner moves both reticle and wafer during exposure; a stepper exposes one full field at a timeA stepper is faster than a scannerScanners use EUV light, steppers use DUVSteppers can print smaller features