Phase Shift Interferometry for Vibrating Wafer Surface Inspection
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Solution Overview
Problem
Existing systems for detecting irregularities on a vibrating wafer surface, such as in a Fizeau interferometer, face challenges with numerical accuracy due to reliance on limited wavelength sets and require extensive processing, leading to inefficiencies and potential errors from residual vibrations and wavelength miscalibration.
Innovation Solution
A method and system that emit a beam of light at multiple wavelengths, cyclically fit signals to the exposed images while the wafer is vibrating, and determine vibration levels and surface irregularities when vibrations drop below a threshold, using computing devices to process images from an image capture device in an interferometer setup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Fourier based phase shift interferometry is used to suppress measurement errors from vibrations, then measurement accuracy is improved, but computational processing complexity and time requirements increase significantly
Solution Approach 1:
The patent segments the interferometry process by capturing multiple images at different phases of vibration cycles rather than requiring complete vibration suppression. This allows the system to process smaller, more manageable data sets from each phase while collectively achieving accurate measurements without the computational burden of full Fourier analysis.
Solution Approach 2:
The patent adapts to the dynamic vibration state of the wafer by capturing images throughout the vibration cycle rather than waiting for static conditions. This dynamic approach enables the system to extract measurement data from moving surfaces while reducing computational requirements compared to traditional methods that require vibration cessation or complex post-processing.
2Productivity
If a limited set of wavelengths is used to increase processing speed, then productivity is improved, but measurement accuracy deteriorates
Solution Approach 1:
The patent employs periodic action by capturing multiple images at different phases of the vibration cycle. This allows the system to accumulate sufficient measurement data through repeated sampling at strategic moments during vibration, achieving both speed and accuracy without requiring a limited wavelength set.
Solution Approach 2:
The patent maintains continuous capture of interference patterns throughout the vibration cycle, ensuring that useful measurement data is collected continuously rather than intermittently. This continuous action enables the system to process data in real-time while maintaining measurement accuracy, eliminating the need to wait for vibrations to cease.
3Measurement precision
If image capture is performed after vibrations stop to ensure stability, then measurement accuracy is improved, but measurement time increases significantly
Solution Approach 1:
The patent performs preliminary capture of interference patterns during the vibration period rather than waiting for vibrations to stop. By capturing images at multiple phases during the vibration cycle, the system prepares measurement data in advance, eliminating the time loss associated with waiting for stable conditions.
Solution Approach 2:
The patent introduces the vibration phase as an intermediary parameter that enables measurement during motion. By using the vibration cycle itself as a timing mechanism for image capture, the system can reference the phase information to accurately measure surface irregularities even though the wafer is vibrating, thus eliminating the need to wait for vibration cessation.
4Reliability
If n-times averaging is performed to suppress noise and vibration errors, then measurement reliability is improved, but computational complexity and processing time increase
Solution Approach 1:
The patent segments the measurement process into discrete capture events at specific vibration phases rather than performing repeated average measurements. This segmentation allows the system to achieve reliable measurements by selecting optimal capture moments during the vibration cycle, reducing the computational burden of extensive averaging while maintaining measurement reliability.
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 approach enables precise and accurate detection of surface irregularities on a vibrating wafer, reducing computational complexity and avoiding delays associated with waiting for vibrations to cease, thereby enhancing the efficiency and accuracy of phase shift interferometry.
Implementation Method 1
emit a beam of light at each of a plurality of wavelengths at a reference plane of the interferometer and at the wafer
Implementation Method 2
exposing an image capture device to reflected light from the reference plane and the wafer
Implementation Method 3
exposing an image capture device to reflected light from the reference plane and the wafer
Implementation Method 4
cyclically fitting, by at least one computing device, a fitted signal to the exposed signal while the wafer is vibrating
Implementation Method 5
cyclically determining, by at least one computing device, a level of vibration of the wafer, based at least in part on the exposed signal
Data Source
AI summary
A method performs phase shift interferometry to detect irregularities of a surface of a wafer after the wafer has been placed into an interferometer and while the wafer is vibrating. Additionally, a system and a non-transitory computer-readable storage medium have computer-executable instructions embodied thereon for performing phase shift interferometry to detect irregularities of a surface of a wafer after the wafer has been placed into an interferometer and while the wafer is vibrating.