Lesson 5 – Form Error Identification & Correction

What You Will Learn

• Recognize center peak vs. center hole and prescribe corrections
• Differentiate edge roll from up edge and adjust dwell/pressure
• Identify astigmatism vs. higher‑order astigmatism
• Tie each signature to actionable machine and process levers
• Document changes and close the loop with metrology

Common Signatures

Center Peak / Center Hole: imbalance of dwell or pressure near the optical center.
Edge Roll: loss of figure near the rim due to pad hydrodynamics or insufficient edge support.
Up Edge: over‑correction or pad stiffening at the boundary.
Astigmatism & Higher Order Astigmatism: non‑axisymmetric terms from fixturing, tool tilt, or kinematic errors.

Corrections

Modify dwell maps, adjust force, and balance relative speeds/ratios. Improve thermal control and ensure pad condition and adhesion are sound. Verify objective/test plate validity before large process moves.

Verification

After changes, reacquire maps (2D/3D) and compare Zernike coefficients to confirm trend direction. Maintain a change log for traceability and faster troubleshooting on repeat jobs.