Oblique Spectral Interferometry Optical System
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Solution Overview
Problem
Conventional optical wafer metrology tools lack optimization of both spectral and interferometric measurements, limiting the amount of information extracted from samples, particularly when performing oblique angle measurements.
Innovation Solution
A novel optical system utilizing an oblique measurement scheme for spectral interferometry, which includes a beam splitting/combining device and a reference reflector, allows for controllable adjustment of optical path differences between sample and reference arms, enabling both oblique spectral interferometric and reflectometric modes, and potentially normal-channel configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional optical wafer metrology tools use separate illumination and collection objectives for oblique measurements, then the measurement setup is straightforward, but the amount of information extracted from the sample is limited
Solution Approach 1:
The patent combines the illumination and collection channels into a single optical path by using a beam splitting/combining device that directs light through the same objective lens. This merging of channels allows the system to maintain the simplicity of separate objectives while enabling interferometric measurements that extract additional phase information from the sample, thereby increasing the total information content without proportionally increasing system complexity.
Solution Approach 2:
The optical system is designed to perform multiple measurement modes (spectral interferometry and reflectometry) using the same hardware components. The beam splitting/combining device and single objective configuration enable the system to function as both an interferometer and a reflectometer, maximizing the information extracted from the sample while avoiding the need for separate specialized measurement systems.
2Measurement precision
If spectral interferometry is implemented with oblique measurement, then phase information can be accessed, but maintaining coherence between reference and sample arms becomes difficult
Solution Approach 1:
The patent employs an asymmetric optical configuration where the beam splitting/combining device creates unequal optical paths for the reference and sample arms. By using a single objective lens for both channels and positioning the beam splitter at a specific angle, the system maintains coherence between the arms despite the oblique measurement geometry, enabling accurate phase extraction while preserving measurement reliability.
3Device complexity
If a single objective is used for both illumination and collection channels, then the optical system becomes more compact, but aligning the channels becomes more difficult
Solution Approach 1:
The beam splitting/combining device is designed to automatically align the illumination and collection channels through its inherent optical geometry. The device uses the reflection and transmission properties of the beam splitter to self-align the two channels, eliminating the need for complex manual alignment procedures and making the compact single-objective configuration easy to operate and maintain.
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 accuracy and quality of measurements by optimizing spectral and interferometric data extraction, providing more detailed information about patterned samples, such as semiconductor wafers, through improved alignment and coherence maintenance.
Implementation Method 1
the interference signal from these two components is then used to extract the spectral phase, since the phase change incurred by the sample causes a change in the fringe pattern of the recombined beams that may be measured
Implementation Method 2
broadband light specularly reflected from the sample is directed along a collection channel
Data Source
AI summary
A measurement system is presented for use in metrology measurements on patterned samples. The system comprises: at least one light source device configured to generate broadband light, at least one detection device configured to provide spectral information of detected light, and an optical system. The optical system comprises at least an oblique channel system for directing incident light generated by the light source(s) along an oblique illumination channel onto a measurement plane, on which a sample is to be located, and directing broadband light specularly reflected from the sample along a collection channel to the detection device(s). The optical system further comprises an interferometric unit comprising a beam splitting/combining device and a reference reflector device. The beam splitting/combining device is accommodated in the illumination and collection channels and divides light propagating in the illumination channel into sample and reference light beams propagating in sample and reference paths, and combines reflected reference and sample paths into the collection channel to thereby create a spectral interference pattern on a detection plane.