IBO (Image-Based Overlay) is the traditional overlay metrology technique that measures alignment between layers by imaging overlay targets — a microscope images box-in-box or bar-in-bar targets, and image processing extracts the registration error from the relative positions of the target features.

IBO Measurement

• Targets: Box-in-box (BiB) or bar-in-bar (AIM marks) — inner box from current layer, outer box from reference layer.
• Imaging: High-magnification brightfield microscopy with optimized illumination wavelength and focus.
• Algorithm: Image processing determines the center of each target element — overlay = center difference.
• Multi-Wavelength: Measure at multiple wavelengths — optimize for signal quality and accuracy.

Why It Matters

• Mature: IBO is the most established overlay technique — decades of calibration and characterization data.
• Large Targets: Traditional BiB targets are large (20-30 µm) — consume valuable scribe line space.
• TIS: Tool-Induced Shift from optical asymmetries — must be calibrated out using 0°/180° measurement.

IBO is measuring alignment with a microscope — the classic overlay metrology technique using optical imaging of registration targets.