Tilted Reference Beam White Light Interferometry for High-Throughput 3D Inspection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional white light interferometry methods face limitations such as low throughput, speckle issues, and fixed sensitivity due to low coherence of the illumination source, which affects the precision and efficiency of 3D measurements in sample inspection systems like PCBs and wafers.
Innovation Solution
A characterization system using a tilted reference beam in white light interferometry, combined with a spatial filter to demodulate interference patterns, allowing for continuous focal adjustment during lateral scanning without the need for multiple z-direction scans, thereby overcoming occlusions and improving sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional white light interferometry is used to scan the z-axis for nanometric precision 3D measurements, then measurement precision is improved, but throughput deteriorates due to the need for multiple z-direction scans
Solution Approach 1:
The patent introduces a tilted reference beam that creates lateral displacement of interference patterns in the x-direction corresponding to z-axis height variations. This transforms the measurement from a one-dimensional z-scanning problem into a two-dimensional problem where height information is encoded in the lateral position of interference fringes, enabling simultaneous capture of 3D information across the entire field of view in a single shot.
Solution Approach 2:
The patent replaces the mechanical z-scanning system with an optical interference-based height encoding system. Instead of physically moving the sample or objective through multiple z-positions to obtain focus information, the tilted beam interferometry encodes height information optically in the lateral displacement of interference patterns, which are then decoded through image processing to retrieve 3D surface topology.
2Productivity
If a tilted reference beam is used to enable lateral scanning without z-direction scans, then throughput is improved, but measurement precision deteriorates without proper demodulation of interference patterns
Solution Approach 1:
The patent introduces a spatial filter as an intermediary optical element that selectively transmits only the tilted reference beam while blocking scattered light and other unwanted optical paths. This spatial filter acts as a mediator that cleans up the interference pattern by removing noise components, thereby preserving measurement precision while enabling the throughputs benefits of single-shot lateral scanning.
Solution Approach 2:
The patent replaces mechanical z-scanning with optical interference pattern demodulation. The lateral displacement of interference fringes caused by the tilted beam is decoded through image processing algorithms that extract height information from the fringe positions, substituting mechanical movement with optical encoding and computational decoding to maintain precision while improving throughput.
3Measurement precision
If conventional interferometry is used, then sensitivity is fixed by the coherence of the illumination source, but adaptability deteriorates when dealing with samples having different spectral responses
Solution Approach 1:
The patent employs a broadband white light source with low temporal coherence, which provides a broad spectral range. The system achieves adaptability to different sample spectral responses by utilizing the wide bandwidth of the white light source, allowing interference to occur across multiple wavelengths simultaneously. This parameter change from monochromatic to broadband illumination enables the system to adapt to varying sample optical properties while maintaining sensitivity through the interference measurement principle.
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 enhances the throughput and sensitivity of 3D measurements by enabling occlusion-free lateral scanning and precise focal adjustment, improving the accuracy of surface height topologies and distance measurements.
Implementation Method 1
white light interferometry using a tilted reference beam relative to the measurement beam... reference element configured to tilt an optical axis of a reference beam relative to an optical axis of a measurement beam... interfere upon the sensor with the light reflected from the reference mirror
Implementation Method 2
utilize a spatial filter to demodulate an interference pattern of the image... utilizing a filter to demodulate an interference pattern of the image
Data Source
AI summary
Systems and methods for characterizing a sample utilizing white light interferometry are disclosed. Such systems and methods may include an optical sub-system. The optical sub-system may include a reference element configured to tilt an optical axis of a reference beam relative to an optical axis of a measurement beam and a sample positioning stage configured to adjust a sample position of a sample along a Z-direction of the sample. Such systems and methods may include receiving an image of the sample. Such systems and methods may include utilizing a filter to demodulate an interference pattern of the image. Such systems and methods may include determining a location of the interference pattern on the image; and directing the focal adjustment based on the location of the interference pattern.