Simultaneous Phase-Shifting Interferometer for Vibration-Insensitive Surface Profiling
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Solution Overview
Problem
Current interferometric systems face challenges in measuring large surface areas at high resolutions efficiently due to sensitivity to vibrations and the need for sequential phase-shifting methods, which are inadequate in dynamic environments or when objects are in motion.
Innovation Solution
A simultaneous phase-shifting interferometer combined with a mechanical scanner and linear pixilated detectors to enable rapid measurement and data transfer, allowing for the generation of multiple phase-shifted interferograms in a single cycle, thereby reducing sensitivity to vibrations and enabling high-speed surface profiling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential phase-shifting methods are used to acquire multiple interferograms, then measurement accuracy is improved, but sensitivity to vibrations and environmental changes increases
Solution Approach 1:
The patent combines multiple phase-shifted interferogram acquisitions into a single temporal instant by using spatially multiplexed optical paths. Four interferograms with different phase shifts (0, 90, 180, 270 degrees) are captured simultaneously through separate optical channels that recombine at a detector array, eliminating temporal separation and thus vibration sensitivity while maintaining measurement accuracy.
Solution Approach 2:
The patent transitions from temporal phase shifting (acquiring interferograms at different times) to spatial phase shifting (acquiring interferograms at different spatial locations/optical paths). By encoding phase information in the spatial domain rather than the temporal domain, the system achieves vibration immunity while preserving measurement precision.
2Measurement precision
If multiple interferograms are acquired sequentially, then phase-shifting accuracy is improved, but measurement time increases
Solution Approach 1:
The patent merges the acquisition of multiple phase-shifted interferograms into a single temporal instant by using spatially multiplexed optical paths. Four interferograms with different phase shifts (0, 90, 180, 270 degrees) are captured simultaneously through separate optical channels that recombine at a detector array, eliminating temporal separation and thus reducing measurement time while maintaining phase-shifting accuracy.
3Productivity
If simultaneous phase-shifting interferometry is used, then measurement speed is improved, but complexity of optical system increases
Solution Approach 1:
The patent segments the optical system into four distinct channels, each handling a specific phase shift. This segmentation allows independent optimization of each channel while maintaining overall system coherence. The use of separate optical paths for each phase shift simplifies the design compared to attempting to implement phase shifting through complex modulators in a single path.
Solution Approach 2:
The patent introduces beam splitters and combiners as intermediary optical elements that facilitate the simultaneous acquisition of multiple phase-shifted interferograms. These intermediaries enable the division and recombination of light paths without requiring complex phase modulation devices, thereby achieving simultaneous measurement while keeping the optical system relatively simple and manageable.
4Device complexity
If temporal phase-shifting methods are used, then device complexity is reduced, but susceptibility to environmental changes increases
Solution Approach 1:
The patent transitions from temporal phase shifting (acquiring interferograms at different times) to spatial phase shifting (acquiring interferograms at different spatial locations/optical paths). By encoding phase information in the spatial domain rather than the temporal domain, the system achieves vibration immunity while preserving measurement precision and maintaining relatively simple 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
This approach allows for accurate and rapid measurement of large surfaces at high resolutions, such as a 300 mm semiconductor wafer in minutes, while maintaining insensitivity to vibrations and environmental changes.
Implementation Method 1
Interferograms are generated by the interference of a test wavefront and a reference wavefront
Implementation Method 2
These methods usually require that the reference and test beams ('beams' and 'wavefronts' used interchangeably herein, with a 'wavefront' being understood as propagating along the optical axis and sweeping out a volume that defines the light beam) be orthogonally polarized
Data Source
AI summary
An optical measuring apparatus for comprising, in combination, a polarization type interferometer including a polarization type beam splitter in which a polarized beam of light is split into orthogonally polarized reference and test beams, an array of detectors arranged in a line for creating a plurality of phase shifting interferograms, and a scanning device for moving the object in a direction perpendicular to a long axis of the detectors.