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.