Diagnostic coverage is the ability to not just detect failures but also identify their root cause location — enabling faster debug, repair, and yield learning by pinpointing which circuit block, net, or component is defective rather than just knowing the device failed.

What Is Diagnostic Coverage?

• Definition: Percentage of failures that can be localized to specific fault sites.
• Purpose: Enable targeted repair, failure analysis, and yield improvement.
• Measurement: (Uniquely diagnosed faults / Total detected faults) × 100%.
• Value: Accelerates root cause analysis and process improvement.

Why Diagnostic Coverage Matters

• Faster Debug: Quickly locate failure source for analysis.
• Yield Learning: Identify systematic defect patterns.
• Repair Enablement: Laser repair or redundancy activation for memory.
• Cost Reduction: Reduce failure analysis time and cost.
• Process Improvement: Link failures to specific process steps.

Diagnostic Resolution Levels

Device Level: Know device failed (lowest resolution). Block Level: Identify failing functional block (CPU, memory, I/O). Net Level: Pinpoint specific signal net with defect. Physical Location: X-Y coordinates for physical failure analysis.

Techniques

Scan Diagnosis: Analyze scan chain failures to locate defects. Logic Diagnosis: Use failing patterns to narrow fault location. Volume Diagnosis: Analyze multiple failures to find common patterns. Layout-Aware Diagnosis: Map logical faults to physical locations.

Applications

• Yield Ramp: Identify and fix systematic defects quickly.
• Memory Repair: Locate bad bits for redundancy replacement.
• Failure Analysis: Guide SEM review to defect location.
• Process Monitoring: Track defect types and locations over time.

Diagnostic coverage is essential for yield learning — the ability to quickly identify where and why devices fail accelerates process improvements and reduces time-to-market for new technologies.