Striped Detector for Layer Thickness Measurement
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Solution Overview
Problem
Current methods for measuring the thickness of layers in semiconductor wafers, such as SOI wafers, are limited by their slow speed, low spatial resolution, and systematic errors due to neglecting the influence of the second layer's thickness variation, making them unsuitable for high-resolution and high-speed production control.
Innovation Solution
A method and assembly that use a detector with striped sensitivity to different wavelength ranges, allowing simultaneous measurement of layer thicknesses with high accuracy and speed, employing a continuous light source and imaging optics to generate images on a detector array, with relative movement to capture multiple wavelength ranges per image point, enabling the determination of multiple layer thicknesses using Taylor series approximations and calibration curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ellipsometric measurements are used to determine layer thickness, then measurement accuracy is improved, but measurement speed deteriorates (requiring several seconds per point)
Solution Approach 1:
The patent extracts only the necessary wavelength information by using a narrow bandwidth filter (10-50 nm) to select a specific wavelength range from the broad spectrum light source. This extraction approach allows the system to achieve ellipsometry-level accuracy for thickness measurement while avoiding the need for full spectral analysis, thereby significantly improving measurement speed for production control applications.
Solution Approach 2:
Instead of performing complete spectral reflectometry across hundreds of wavelength points, the patent applies partial action by measuring reflectance at a limited, optimized wavelength range (10-50 nm bandwidth). This partial measurement approach provides sufficient accuracy for thickness determination while dramatically reducing the number of measurements required, thus resolving the speed-accuracy contradiction.
2Measurement precision
If spectral reflectometry with hundreds of wavelength points is used, then measurement accuracy is improved, but measurement speed deteriorates (too slow for high speed mapping)
Solution Approach 1:
The patent extracts only the critical wavelength information needed for thickness measurement by using a narrow bandwidth filter (10-50 nm) to select a specific wavelength range. This extraction eliminates the need to collect and process hundreds of spectral points, achieving sufficient accuracy while enabling high-speed mapping suitable for production control.
Solution Approach 2:
The patent applies partial action by performing reflectance measurement at a limited wavelength range (10-50 nm bandwidth) rather than across the full spectrum. This partial measurement provides adequate accuracy for thickness determination while dramatically reducing measurement time, thus resolving the speed-accuracy contradiction for high-speed mapping applications.
3Productivity
If intensity measurement at a single wavelength is used, then measurement speed is improved, but measurement precision deteriorates (systematic errors from neglecting second layer influence)
Solution Approach 1:
The patent applies partial action by measuring reflectance at a narrow bandwidth (10-50 nm) rather than a single wavelength point. This partial spectral information captures enough variation to account for the influence of the second layer on the optical response, thereby improving measurement accuracy while maintaining the speed advantage of single-point spectral measurement.
Solution Approach 2:
The patent changes the measurement parameter from a single wavelength intensity measurement to a narrow bandwidth spectral measurement. By measuring reflectance across a small wavelength range (10-50 nm), the system captures the spectral variation caused by interference effects that reveal the second layer's thickness influence, thus improving precision while maintaining high speed.
4Measurement precision
If narrow bandwidth filtering (10-50 nm) is applied, then measurement precision is improved by capturing spectral variation, but device complexity increases (additional optical components)
Solution Approach 1:
The patent segments the broad spectrum light into multiple wavelength ranges using a narrow bandwidth filter (10-50 nm). This segmentation allows the system to capture the essential spectral variation needed for accurate thickness measurement while keeping the filtering mechanism simple and the optical path straightforward, thus balancing precision improvement with acceptable device complexity.
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 accurate and efficient measurement of layer thicknesses with high lateral resolution and speed, reducing the need for extensive spectral evaluation methods like ellipsometry, and providing precise thickness determination of multiple layers without significant systematic errors.
Implementation Method 1
The light is reflected at the interfaces between the layers or transmitted by the layers and finally detected
Implementation Method 2
The intensity of the light reflected by a two layer stack on top of a substrate varies strongly with the wavelength range due to the interference of the optical waves in dependence of the thicknesses of the layers
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
A method and an inspection assembly for determining the thickness of one or more layers of a sample stack of layers or other properties influencing the intensity of light reflected by the sample stack with an assembly comprising a light source for illuminating the sample stack of layers and a camera with a detector for detecting the intensity of light reflected by the sample stack of layers in defined wavelength ranges, the method comprising the steps of illuminating the sample stack of layers with light from the light source; detecting the intensity of light reflected by the sample stack of layers with the detector in different wavelength ranges; and determining the thickness or other property from the intensity detected by the detector; are characterized in that the detector is an array detector with a plurality of detector elements in lines and columns; an image of the sample stack of layers is generated on the detector; the detector comprises a plurality of sections in the form of parallel stripes, the stripes detecting the light reflected by the sample stack of layers simultaneously; light of one selected wavelength range only is detected by each of the plurality of sections of the detector; and a movement of the image of the sample stack of layers on the detector or of the parallel stripes is generated in a direction perpendicular to the longitudinal direction of the parallel stripes such that each point of the inspected sample stack of layers is detected at least once in each of the different wavelength ranges.