A Spectroscopic Reflectance-Based Low-Cost Thickness Measurement System for Thin Films: Development and Testing

Area of Science:

• Materials Science
• Optical Engineering
• Spectroscopy

Background:

• Roll-to-roll (R2R) processing requires cost-effective, scalable thin film inspection methods.
• Existing methods for thin film analysis often face limitations in cost, dimension, and feedback control.
• There is a growing need for advanced sensors to enhance R2R process control and quality assurance.

Purpose of the Study:

• To develop and validate a novel, low-cost spectroscopic reflectance system for accurate thin film thickness measurements.
• To explore the integration of reduced-size spectrometer sensors for enhanced R2R processing.
• To enable new control feedback options for thin film deposition and inspection.

Main Methods:

• Hardware and software development of a spectroscopic reflectance system utilizing two advanced, low-cost sensors.
• Optimization of parameters including LED light intensity, microprocessor integration time, and sensor-to-sample distance.
• Application of curve fitting and interference interval methods for reflectance calculations and error analysis.

Main Results:

• The proposed system achieved lower root mean squared error (RMSE) of 0.022 and normalized mean squared error (MSE) of 0.054 using the curve fitting method.
• The interference interval method demonstrated a comparative error of 0.09 against expected modeled values.
• The system proved effective in thin film thickness measurements, outperforming a HAL/DEUT light source in specific error metrics.

Conclusions:

• The developed spectroscopic system provides a viable, low-cost solution for thin film thickness measurement in R2R manufacturing.
• This technology enables the expansion of multi-sensor arrays for comprehensive thin film analysis.
• Potential applications include in-line monitoring and quality control in dynamic or moving environments.