Porous Layer Reflectance Analysis 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 significant equipment, and are not suitable for substrates with non-flat surfaces, especially in applications like solar cells where spatial resolution and non-destructive analysis are needed.
Innovation Solution
A method using reflectance curve analysis with non-linear least squares fitting, employing predetermined start values for layer thickness, porosity, and roughness, which can be automatically set based on manufacturing knowledge and reflectance curve fluctuations, to determine these properties with high accuracy and spatial resolution.
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 measurement precision is poor and the method is destructive
Solution Approach 1:
The patent replaces the mechanical gravimetric measurement system with an optical measurement system. Instead of measuring mass changes mechanically, the invention uses optical reflectance measurements to determine layer thickness and porosity, achieving both non-destructive measurement and spatial resolution while maintaining relative equipment simplicity.
Solution Approach 2:
The patent introduces optical reflectance as an intermediary parameter to indirectly determine physical properties. Rather than directly measuring thickness or porosity, the system measures optical reflectance and uses modeling to derive the desired parameters, enabling non-destructive measurement with spatial resolution.
2Measurement precision
If ellipsometry measurements are used to determine layer properties, then measurement precision is improved, but the method requires flat substrate surfaces and is not robust
Solution Approach 1:
The patent changes the measurement parameters from ellipsometry (which requires flat surfaces) to reflectance measurements at multiple angles and wavelengths. This parameter change allows the measurement to work on rough or non-flat substrate surfaces while still providing accurate determination of layer properties through computational modeling.
3Reliability
If reflectance methods are used to determine physical properties, then non-destructive measurement with spatial information is achieved, but previous approaches required great deal of equipment and time
Solution Approach 1:
The patent performs reflectance measurements at a limited set of specific angles and wavelengths that are sufficient to determine the key parameters (thickness, porosity, roughness). Rather than performing exhaustive measurements across all angles and wavelengths, the method uses a partial set of measurements combined with modeling to achieve the desired information with reduced equipment and time requirements.
Solution Approach 2:
The patent uses preliminary knowledge of the layer structure and optical properties to guide the measurement process. By having prior information about the expected range of parameters and the optical model of the system, the measurement can be optimized to require fewer data points and less complex equipment while still achieving accurate results.
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, fast, and non-destructive determination of porous layer properties, suitable for both single and multiple layers, with minimal user intervention and equipment, enabling spatially resolved maps of layer thickness, porosity, and roughness.
Implementation Method 1
reflectance curve concerning light irradiated onto the porous layer
Implementation Method 2
periodic fluctuations of reflectance intensities within the recorded reflectance curve
Data Source
AI summary
A method and an apparatus (15) for computer-implemented determination of physical properties of a porous layer (1) present on a surface of a substrate. The physical properties include at least a layer thickness (d) of the layer, a porosity (p) of the layer and a roughness (r) of the layer at an interface (9) with the substrate supporting the layer. The method includes recording a reflectance curve (39) concerning light (25) irradiated onto the porous layer within a wavelength range in which the porous layer is largely transparent, setting a predetermined roughness start value, setting a porosity start value based on knowledge concerning a manufacturing process for forming the porous layer, setting a layer thickness start value based on an evaluation of periodic fluctuations of reflectance intensities within the recorded reflectance curve, and determining the physical properties of the porous layer by computer-implemented fitting of the recorded reflectance curve using a non-linear least squares method.