diagnostic coverage
**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.