Tunable Light Source Interferometer for Semiconductor Surface Metrology
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Solution Overview
Problem
Current interferometers face challenges in accurately determining the distance between a reference surface and raised surface features on a sample, particularly in semiconductor devices, due to limitations in measuring small displacements and surface topography over large areas with high precision.
Innovation Solution
The implementation of a tunable light source system that emits multiple light beams of different wavelengths, combined with digital imagers and a processor system, generates interference patterns to determine distances between reference and raised surface features by coherent addition of reflections, utilizing techniques like Fast Fourier Transform to analyze intensity values and construct fringe patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional interferometers are used to measure surface topography, then measurement capability is provided, but measurement precision deteriorates for small displacements and large areas
Solution Approach 1:
The patent segments the measurement process by using multiple discrete wavelength beams (e.g., 405nm, 532nm, 635nm) to measure different depth ranges. Each wavelength provides optimized precision for specific displacement magnitudes, allowing the system to maintain high measurement precision across large areas by selecting appropriate wavelengths for different regions.
Solution Approach 2:
The system changes the optical parameter (wavelength) of the light source to adapt to different measurement requirements. By tuning the wavelength of the laser beams, the interferometer can optimize the coherence length and sensitivity for measuring both small displacements and large area topography, thereby improving measurement precision across varying scales.
2Measurement precision
If multiple wavelengths are used to improve measurement range, then measurement capability is enhanced, but device complexity increases
Solution Approach 1:
The patent combines multiple wavelength lasers and their respective optical paths into a single integrated interferometer system. The beam combining optics merge the different wavelength beams into a common measurement path, allowing simultaneous multi-wavelength measurement without requiring separate interferometer systems for each wavelength, thus enhancing measurement capability while controlling device complexity.
Solution Approach 2:
The interferometer system is designed with universal components that can handle multiple wavelengths simultaneously. The optical system, including beam splitters, mirrors, and detectors, is configured to process different wavelength beams through the same measurement path, enabling the single device to perform multiple measurement functions across different depth ranges and surface conditions.
3Measurement precision
If coherent addition of reflections is used to determine distance, then measurement accuracy is improved, but difficulty of detecting and measuring increases
Solution Approach 1:
The patent replaces complex manual analysis of interference patterns with automated digital image processing and computational algorithms. The detector captures interference fringes, and software automatically analyzes the fringe patterns to extract precise distance measurements, eliminating the need for manual measurement and reducing the difficulty of detecting and measuring surface topography.
Solution Approach 2:
The system introduces digital imaging technology as an intermediary between the optical interference process and the final measurement result. The detector converts optical interference patterns into digital images, which can then be processed using image processing algorithms to automatically determine surface height and topography, thereby simplifying the detection and measurement process while maintaining high accuracy.
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 measurement of distances and topography of semiconductor surfaces, improving the accuracy and efficiency of surface feature inspection and defect detection, allowing for simultaneous brightfield, darkfield, and fluorescence imaging.
Implementation Method 1
The reflected beam may be a coherent addition of a first reflection of the beam off the surface of the reference plate, a second reflection of the beam off the raised surface feature and a third reflection off the floor of the sample or substrate
Implementation Method 2
a first reflection of the beam off the surface of the reference plate, a second reflection of the beam off the raised surface feature and a third reflection off the floor of the sample
Data Source
AI summary
An interferometer and an imager may include a tunable light source, a beam splitter, a digital imager, and a processor system. The tunable light source may be configured to emit a beam. The beam splitter may be configured to direct the beam toward a sample with a floor surface and a raised surface feature. The digital imager may be configured to receive a reflected beam and to generate an image based on the reflected beam. The reflected beam may be a coherent addition of a first reflection of the beam off a reference plate and a second reflection of the beam off the raised surface feature and third reflection of the beam off the floor surface. The processor system may be coupled to the digital imager and may be configured to determine a distance between the reference surface and the feature surface based on the image. A second digital imager may also be configured to receive a reflected beam and scattered beam to generate a two-dimensional grayscale image of the surface based on these beams and may also be configured to receive fluorescent light generated by the incident light to generate a two-dimensional gray scale an image of the surface based on fluorescent emission.