Anti-Interference Spectral Confocal Sensors Based on Line Spot

Area of Science:

• Optoelectronics
• Metrology
• Surface Science

Background:

• Spectral confocal displacement sensors offer high accuracy but face challenges with vibrations, angular deflection, and surface variations.
• These challenges limit sensor stability and accuracy in critical applications like lithium battery wafer analysis and optical component metrology.
• Existing point-based sensors struggle with dynamic measurement stability.

Purpose of the Study:

• To develop and validate a novel line-spot-based confocal measurement method for enhanced sensor stability and accuracy.
• To address the limitations of traditional point spectral confocal sensors in dynamic and challenging measurement environments.
• To optimize a confocal system using optical simulation for improved performance in wafer thickness and surface topography measurements.

Main Methods:

• A line-spot measurement approach was designed using a binary diffractive lens and a cylindrical lens with a 20× objective.
• The optical system's structure was simulated and optimized using ZEMAX optical software.
• The system was calibrated using a nanometer displacement stage for precise performance evaluation.

Main Results:

• The optimized confocal system achieved a measurement range of 800 μm and a line spot measuring 3.8 mm in length and 0.2 mm in width.
• The sensor demonstrated a high resolution of 30 nm.
• Significantly improved dynamic stability was observed, with a standard deviation (SD) of 0.013 μm, compared to a point spectral confocal sensor's SD of 0.064 μm.

Conclusions:

• The proposed line-spot-based spectral confocal sensor exhibits superior dynamic stability during scanning measurements.
• The enhanced sensor design effectively mitigates issues related to vibration and surface quality variations.
• This method provides a more robust and accurate solution for non-contact metrology in demanding applications.