spatial signature

**Spatial signature** is the **characteristic pattern of failures on a wafer** — the unique fingerprint of a process issue, equipment problem, or systematic defect that appears consistently across wafers. **What Is Spatial Signature?** - **Definition**: Repeating spatial pattern of defects or failures. - **Purpose**: Identify root cause, correlate with process steps. - **Characteristics**: Consistent pattern across multiple wafers. **Common Signatures** **Center Hot**: Higher failures at wafer center (CMP dishing, implant dose). **Edge Ring**: Failures at wafer edge (etch loading, deposition uniformity). **Quadrant Effect**: One quadrant worse (equipment asymmetry). **Radial Pattern**: Spoke-like pattern (spin coating, temperature gradient). **Reticle Repeat**: Pattern repeats at reticle step size (mask defect). **Root Cause Correlation** - Match signature to known process issues. - Correlate with equipment maintenance records. - Compare across process steps to isolate cause. - Use statistical analysis to confirm correlation. **Applications**: Root cause analysis, equipment troubleshooting, process optimization, preventive maintenance. Spatial signature is **defect fingerprint** — each process issue leaves characteristic pattern that guides engineers to root cause.