obirch (optical beam induced resistance change)

**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.