Porous Layer Reflectance Fitting for Non-Destructive Property Mapping
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Solution Overview
Problem
Existing methods for determining the physical properties of porous layers on substrates, such as layer thickness, porosity, and roughness, are often inaccurate, destructive, require flat substrate surfaces, and are time-consuming, especially when dealing with non-flat substrates.
Innovation Solution
A method using nonlinear least squares fitting of reflection profiles, with automated setting of starting values based on manufacturing knowledge and reflection intensity analysis, to determine layer thickness, porosity, and roughness of porous layers, applicable to single and multiple layers, without destroying the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If gravimetric method is used to determine porosity and thickness, then measurement can be performed with simple equipment, but the method provides only spatially averaged values and suffers from high inaccuracies
Solution Approach 1:
The patent divides the measurement into multiple discrete locations across the substrate surface. By performing reflectance measurements at multiple positions and combining the data, the method achieves spatially resolved information about layer thickness and porosity while using relatively simple optical equipment.
Solution Approach 2:
The patent transitions from measuring a single averaged value to measuring across multiple spatial dimensions. By scanning the substrate surface and collecting reflectance data at different positions, the method creates a spatial map of physical properties, adding the dimension of spatial resolution to the measurement.
2Measurement precision
If ellipsometry measurements are used to determine layer properties, then spatial information about thickness and porosity can be obtained, but the method requires relatively flat substrate surfaces and is not robust
Solution Approach 1:
The patent measures reflectance across a broad wavelength range rather than at a single angle or wavelength. By analyzing the spectral dependence of reflectance at multiple wavelengths, the method can extract layer properties without requiring the substrate to be optically flat, making it applicable to rough or textured surfaces.
Solution Approach 2:
The patent replaces the mechanical/optical alignment requirements of ellipsometry with a reflectance measurement system that is less sensitive to surface flatness. By using intensity-based reflectance measurements across wavelengths rather than polarization-based ellipsometry, the method eliminates the need for precise optical alignment and flat surfaces.
3Reliability
If reflection methods are used to determine porous layer properties, then non-destructive measurement with spatial resolution can be achieved, but previous approaches required high equipment expenditure and time
Solution Approach 1:
The patent uses a single broadband light source and detector system that can measure reflectance across a wide wavelength range. This multi-functional setup allows the same equipment to provide information about both layer thickness and porosity simultaneously, eliminating the need for multiple specialized instruments.
Solution Approach 2:
The patent performs reflectance measurements continuously across a broad wavelength spectrum rather than at discrete points. By collecting spectral data over a continuous wavelength range and analyzing the full spectrum, the method extracts multiple physical parameters from a single measurement sequence, reducing total measurement time.
4Measurement precision
If multiple measurement locations are used to obtain spatial information, then accuracy of physical property determination is improved, but measurement time increases
Solution Approach 1:
The patent performs a preliminary spectral measurement across the full wavelength range at each location before analyzing specific parameters. By collecting all spectral data first and then processing it to extract thickness, porosity, and other properties, the method avoids repeated measurements and optimizes data usage to reduce total measurement time.
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
Provides reliable, rapid, and non-destructive determination of porous layer properties with minimal equipment, enabling spatial resolution and automation, suitable for various manufacturing processes.
Implementation Method 1
Detecting a reflection profile relating to light irradiated onto the porous layer within a wavelength range in which the porous layer is largely transparent
Data Source
Figure 1
Figure 2~3
AI summary
Described are a method and a device (15) for the computer-assisted determination of physical properties of a porous layer (1) disposed on a surface of a substrate (3). The physical properties comprise at least a layer thickness (d) of the layer, a porosity (p) of the layer and a roughness (r) of the layer at a boundary surface (9) to the substrate carrying the layer. The method comprises: - acquiring a reflection profile (39) of the light (25) incident on the porous layer within a wavelength range in which the porous layer is largely transparent, - setting a predefined roughness start value, - setting a porosity start value based on knowledge of a production process for forming the porous layer, - setting a layer thickness start value based on an evaluation of periodic fluctuations in reflection intensities within the reflection profile acquired, - determining the physical properties of the porous layer by computer-assisted fitting of the acquired reflection profile using a nonlinear least squares method, for example a Levenberg-Marquardt algorithm or a trust region method, proceeding from the roughness start value, the porosity start value and the layer thickness start value.