Confocal signal evaluation algorithms for surface metrology: uncertainty and numerical efficiency.

Area of Science:

• Surface metrology and optical measurement techniques.

Background:

• Confocal microscopy offers superior lateral resolution but its axial resolution is limited by noise affecting signal evaluation algorithms.
• Common algorithms like center-of-mass, parabolic least-square fit, and cross-correlation are susceptible to noise.

Purpose of the Study:

• To analyze the impact of various noise sources on confocal microscopy signal evaluation algorithms.
• To provide analytical solutions for height evaluation uncertainty in surface microstructures.
• To guide the selection of optimal measurement parameters for improved efficiency.

Main Methods:

• Derivation of closed-form results for height evaluation uncertainty.
• Inclusion of factors like the number of axial intensity values and pre-evaluation thresholds.
• Verification through numerical Monte Carlo simulations and analysis of algorithm efficiency.

Main Results:

• Quantified the influence of noise on different confocal signal evaluation algorithms.
• Provided analytical expressions for uncertainty in height measurements.
• Demonstrated the validity of derived results through simulations.

Conclusions:

• Noise significantly impacts axial resolution in confocal microscopy.
• The derived results offer a basis for optimizing measurement parameters.
• This can lead to reduced measurement times in practical surface topography applications.