OBIRCH (Optical Beam Induced Resistance Change) is a laser-based failure analysis technique — that scans a focused laser beam across the IC surface while monitoring changes in resistance (current), pinpointing resistive defects like voids, cracks, or thin metal lines.

What Is OBIRCH?

• Principle: The laser locally heats the metal. If a resistive defect exists, heating changes its resistance, causing a measurable change in current ($Delta I$).
• Normal Metal: Small, predictable $Delta I$ (positive temperature coefficient).
• Defect: Anomalously large or inverse $Delta I$ indicates a void, crack, or contamination.
• Resolution: ~1 $mu m$ (determined by laser spot size).

Why It Matters

• Interconnect Defects: The go-to technique for finding electromigration voids, stress migration cracks, and via failures.
• Non-Destructive: Performed on powered, functioning devices.
• Complementary: Often used with EMMI (finds active defects) while OBIRCH finds passive resistive ones.

OBIRCH is the metal doctor for ICs — diagnosing hidden resistive diseases in the interconnect metallization by feeling for changes under laser stimulation.