Confocal Microscopy Layer Thickness and Refractive Index Determination
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Solution Overview
Problem
Current methods for determining the thickness and refractive index of a layer on a substrate require complex spectrally resolved measurements, often necessitating high spectral resolution and multiple assumptions, which is technically cumbersome and resource-intensive.
Innovation Solution
A method using confocal microscopy to image the layer at multiple axial positions, capturing intensity distributions to determine the apparent thickness and shape features, allowing for the simultaneous measurement of layer thickness and refractive index without spectral analysis, utilizing existing confocal microscopes with a single monochromatic light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spectrally resolved reflection measurements are used to determine layer thickness and refractive index, then both parameters can be determined from the position of local extrema, but the spectral resolution required is very high and the technical outlay increases
Solution Approach 1:
The patent replaces the complex spectral measurement system with a confocal optical system using a single monochromatic light source. Instead of measuring reflection spectra and analyzing local extrema positions, the system captures intensity distributions (point spread functions) at multiple axial positions and determines layer parameters from the axial distance between maxima and shape feature comparisons, eliminating the need for high spectral resolution equipment
Solution Approach 2:
The patent changes the measurement parameter from spectral wavelength to axial position. By varying the axial position of the object plane and capturing intensity distributions at different z-positions, the system encodes layer thickness information in the axial distance between maxima and refractive index information in the shape feature differences, avoiding spectral analysis entirely
2Measurement precision
If ellipsometry is used to ascertain layer thickness and refractive index, then both parameters can be determined, but spectrally resolved measurement and multiple assumptions about the sample are required
Solution Approach 1:
The patent replaces the ellipsometry measurement system with confocal optical imaging. Instead of measuring polarization changes and performing complex mathematical modeling with multiple assumptions about sample properties, the system directly images the layer at multiple axial positions and determines thickness and refractive index from the axial distance and shape feature comparisons of the captured intensity distributions
Solution Approach 2:
The patent uses the optical system's inherent depth sectioning capability and point spread function characteristics to self-determine layer parameters. The confocal system naturally provides axial resolution and the shape features of the intensity distributions contain encoded information about the layer properties, eliminating the need for external spectral measurements and complex modeling assumptions
3Device complexity
If a single monochromatic light source is used in confocal microscopy, then technical complexity and resource requirements are reduced, but traditionally only intensity information without spectral content is available
Solution Approach 1:
The patent compensates for the loss of spectral information by utilizing the axial dimension. By capturing intensity distributions at multiple axial positions and analyzing the axial distance between maxima and shape feature differences, the system extracts both layer thickness and refractive index information from the spatial distribution of light intensity along the optical axis, replacing the spectral dimension with an axial dimension
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
Enables independent determination of layer thickness and refractive index, reducing technical complexity and resource requirements, and allowing for characterization of multilayer systems without altering existing microscope optics.
Implementation Method 1
the layer is imaged at a plurality of axial positions along an optical axis in confocal microscopic fashion
Implementation Method 2
A respective intensity distribution along the optical axis is captured from these image representations of the two faces
Data Source
AI summary
The invention relates to a method for determining the thickness and refractive index of a layer (6) on a substrate (26). The layer (6) having a layer boundary surface (30) facing the substrate (26) and a layer top side (28) facing away from the substrate (26). In said method, the following steps are performed; imaging the layer (6), by confocal microscopy, along an optical axis (8), determining a point spread function resolved along the optical axis (8) al the layer boundary surface (30) and the layer lop side (28), determining an apparent thickness of the layer at a lateral point of the layer from the distance between two maxima of the point spread function, determining the widening of a maximum that the point spread function has at the layer boundary surface (30) relative to the width of the same maximum that the point spread function has at the layer top side (28), at the lateral point, and determining the thickness and refractive index of the layer (6) at the lateral point from the apparent thickness and the widening.