Differential confocal over-range determination method based on an information theory.

Area of Science:

• Optical Metrology
• 3D Surface Profilometry
• Confocal Microscopy

Background:

• Existing differential confocal axial 3D measurement lacks a method to verify if sample surface heights are within the effective measurement range.
• This limitation hinders accurate 3D shape determination and data reliability.

Purpose of the Study:

• To propose and validate an information theory-based differential confocal over-range determination method (IT-ORDM).
• To enable precise determination of whether sample surface height data falls within the effective measurement range of differential confocal axial measurements.

Main Methods:

• The IT-ORDM establishes the axial effective measurement range boundaries using the differential confocal axial light intensity response curve.
• It determines effective intensity measurement ranges for pre-focus and post-focus axial response curves (ARC).
• An intersection operation on effective measurement pre-focus and post-focus images extracts the differential confocal image's effective measurement area.

Main Results:

• The IT-ORDM successfully identifies the boundaries of the axial effective measurement range.
• It accurately determines the effective measurement ranges for pre-focus and post-focus ARCs.
• Experimental results demonstrate effective determination and restoration of the 3D sample surface shape at the reference plane.

Conclusions:

• The proposed IT-ORDM effectively addresses the limitation of existing differential confocal axial 3D measurement methods.
• This method ensures the reliability of 3D surface height measurements by confirming data is within the effective range.
• IT-ORDM facilitates accurate 3D shape restoration of sample surfaces.