Vibration-Insensitive Interferometry for Multilayer Thin-Film Thickness
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Solution Overview
Problem
Existing methods for measuring the thickness and profile of multilayer thin films are limited by large spot sizes, long measurement times, and inability to account for external vibrations and environmental changes, making them unsuitable for industrial production settings.
Innovation Solution
A vibration-insensitive interferometry method using a polarizing beam splitter, quarter-wave plates, a shutter, and a pixelated polarizing camera to acquire phase-shifted interference signal images and reflectance images, enabling simultaneous thickness and profile measurement of multilayer films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large spot size of 25 μm or more is used in ellipsometer measurement, then the measurement can be performed, but the measurement time becomes long and spatial resolution is low
Solution Approach 1:
The measurement system divides the measurement process into multiple parallel channels: a reference flat measurement channel and a measurement object measurement channel. Each channel can independently acquire interference signals, allowing simultaneous measurement of multiple parameters without sequential scanning, thus reducing total measurement time while maintaining precision.
Solution Approach 2:
The patent introduces a wavelength dimension by using a broad-band light source and measuring interference signals across multiple wavelengths simultaneously. This allows the system to extract multiple film parameters (thickness, refractive index, profile) from a single measurement process, reducing measurement time compared to single-wavelength sequential measurement.
2Measurement precision
If a single point measurement manner is used, then thickness measurement is possible, but profile measurement of each layer is not allowed
Solution Approach 1:
The measurement system is designed to perform multiple measurement functions simultaneously. The same interference measurement apparatus can measure both the thickness of individual layers and the overall profile of the multilayer film structure by analyzing interference signals at different wavelengths and positions, eliminating the need for separate measurement processes.
Solution Approach 2:
The patent measures film profile by analyzing interference signals across different spatial positions and wavelengths, adding spatial and spectral dimensions to the measurement. This allows extraction of profile information (layer thickness variations, surface morphology) in addition to single-point thickness measurements.
3Measurement precision
If conventional ellipsometer measurement is used, then film parameters can be measured, but the system is sensitive to external vibrations and environmental changes
Solution Approach 1:
The patent introduces a reference flat as an intermediary element in the measurement system. By measuring the interference signal from the reference flat and using it to compensate for environmental variations, the system eliminates the harmful effect of vibrations and environmental changes on measurement precision. The reference flat acts as a stabilizing intermediary that references out external disturbances.
4Measurement precision
If continuous changing of incident angle and wavelength is performed, then polarization state changes can be measured, but the measurement process becomes complex and time-consuming
Solution Approach 1:
The patent pre-calculates and stores the expected interference signal patterns for different film structures and parameters. During measurement, the system compares actual interference signals against these pre-computed references to quickly identify film characteristics, eliminating the need for complex real-time analysis and reducing measurement time while maintaining precision.
Solution Approach 2:
The measurement system continuously acquires interference signals across multiple wavelengths simultaneously rather than sequentially changing parameters. This continuous multi-wavelength measurement approach maintains measurement precision while significantly reducing the time required compared to sequential parameter scanning.
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 method allows for rapid and accurate measurement of both thickness and profile of multilayer thin films, while being insensitive to external vibrations and environmental changes, making it suitable for industrial production testing.
Implementation Method 1
a polarizing beam splitter that reflects a first polarized wave of light emitted from the illumination optical module, and transmits a second polarized wave
Implementation Method 2
a third quarter-wave plate that generates interference signals by occurring phase lag of the second polarized reflected wave and the first polarized reflected wave
Implementation Method 3
generating interference signals by occurring phase lag of the second polarized reflected wave and the first polarized reflected wave
Data Source
AI summary
The present disclosure relates to an apparatus and a method for a thickness and a profile of a multilayer thin film using a vibration insensitive interference method are provided, which allow measuring the phase of a measurement object by acquiring a plurality of different phase-shifted interference signal images at a time through interference signals between a reference flat and the measurement object by a polarizing beam splitter, a quarter-wave plate, a shutter and a pixelated polarizing camera, and which also allow measuring reflectance of the measurement object by acquiring a plurality of reflected signal images obtained at a time through respective reflected lights for each of a reference surface and the measurement object by a plurality of different polarizers.