Coating Thickness Measurement on Thin Substrates Using Oblique IR Reflection
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Solution Overview
Problem
Existing methods for determining the layer thickness or surface area coverage of thin coatings on thin or transparent substrates, particularly those with varying thicknesses, are unreliable due to thin-film interferences and substrate curvature, making precise measurement challenging, especially in inline production environments.
Innovation Solution
The method involves varying the angle of incidence of electromagnetic characterization radiation relative to the substrate surface by at least 20 degrees to average out thin-film interference effects, using broadband infrared radiation with a characterization wavelength range adapted to the coating's absorption band, and optionally incorporating a reflective surface or reference radiation to enhance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If infrared reflection absorption spectroscopy is used to measure coating thickness, then measurement capability is provided, but measurement reliability deteriorates due to thin-film interferences and substrate curvature
Solution Approach 1:
The patent changes the measurement parameter from normal incidence to oblique incidence angles (at least 20 degrees relative to the surface normal). This parameter change in the angle of incidence causes thin-film interference effects to cancel out, thereby improving measurement reliability while maintaining coating thickness measurement capability.
2Difficulty of detecting and measuring
If conventional infrared spectrometers are used, then coating characterization is possible, but device complexity and cost increase
Solution Approach 1:
The patent extracts the essential measurement function from complex infrared spectrometers by using a simplified setup with broadband infrared radiation source and a single detector. Only the necessary components for measuring coating absorption are retained, while complex spectral analysis capabilities are removed, reducing device complexity and cost.
Solution Approach 2:
The patent employs a universal measurement approach using broadband infrared radiation that can detect coating absorption across multiple wavelengths simultaneously. This multi-functional capability allows a single simplified instrument to perform various coating characterization tasks without requiring multiple specialized devices.
3Adaptability or versatility
If measurement is performed on thin substrates with varying thickness, then real-world application is achieved, but measurement precision deteriorates due to substrate thickness variations
Solution Approach 1:
The patent changes the measurement geometry to oblique incidence, which causes the measurement to become insensitive to substrate thickness variations. The interference effects that normally depend on substrate thickness cancel out at oblique angles, allowing precise coating measurement even on thin substrates with varying thickness.
4Productivity
If inline testing is implemented for 100% inspection, then productivity is improved, but measurement speed requirements increase
Solution Approach 1:
The patent enables continuous measurement by using broadband infrared radiation that can simultaneously characterize coatings across the entire substrate surface without requiring point-by-point scanning. This continuous measurement approach maintains 100% inspection coverage while achieving high measurement speeds suitable for inline production environments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise determination of layer thickness and surface coverage density on thin substrates, suitable for inline testing, by minimizing interference and alignment errors, thus ensuring high measurement accuracy and speed.
Implementation Method 1
the coating has an absorption band within the characterization wavelength range
Implementation Method 2
detecting a characterization intensity of the characterization radiation reflected back by the test object or a reflective surface behind the test object
Data Source
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AI summary
The present invention relates to a method for determining the layer thickness or surface area density of a coating of a test object, wherein the test object comprises the coating and a substrate with a substrate thickness, wherein the coating is applied to the substrate, wherein the layer thickness is less than the substrate thickness, and wherein the method comprises the steps of: generating electromagnetic characterization radiation with a characterization wavelength range from 780 nanometers to 1 millimeter, wherein the coating has an absorption band within the characterization wavelength range; illuminating the test object with the characterization radiation.Detecting the characterization intensity of the characterization radiation reflected from the test object or a reflective surface behind the test object and deriving the layer thickness or the surface coverage density from the characterization intensity. According to the invention, the substrate thickness is 250 micrometers or less, and the illumination and detection are carried out such that the characterization radiation detected varies in at least one plane over a range of at least 20 degrees with respect to a normal on a surface of the coating.