Pupil Plane White Light Interferometry for Sub-Diffraction Semiconductor Metrology
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Solution Overview
Problem
Current scanning white-light interferometry systems face limitations in achieving diffraction-limited spot sizes for characterizing patterned semiconductor features, as they are constrained by the diffraction limit and struggle to accurately determine the center of the pupil plane, especially when dealing with patterned structures.
Innovation Solution
A white light interferometric metrology device operates in the image and objective pupil plane, extracting an electric field with complex parameters to determine sample characteristics using an electric field model specific to the zero diffraction order, allowing for a Fourier transform of interferometric data to determine the pupil center and convert pixel data into unique sets of angle of incidence and azimuth angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If scanning white-light interferometry operates in the image plane, then surface height profiles can be obtained, but the spot size is limited by diffraction and structural information of patterned features cannot be accurately extracted
Solution Approach 1:
The patent inverts the conventional operation plane from the image plane to the objective pupil plane. By capturing interferometric data in the pupil plane and performing Fourier transform to convert pixels into angle of incidence and azimuth angle, the system extracts structural information with enhanced precision while achieving spot sizes below the diffraction limit.
Solution Approach 2:
The patent transitions from two-dimensional image plane detection to three-dimensional pupil plane detection by incorporating angular information (angle of incidence and azimuth angle) as additional dimensions. This dimensional expansion enables simultaneous measurement of wavelength and angle dependencies, providing comprehensive structural characterization beyond conventional height profiling.
2Adaptability or versatility
If conventional interferometric measurement is used, then intensity data can be obtained, but wavelength-angle dependencies and continuous spectral information cannot be simultaneously measured
Solution Approach 1:
The patent creates a multi-functional measurement system that simultaneously captures wavelength spectrum, angle of incidence, and azimuth angle information in a single pupil plane measurement. The Fourier transform processing converts the pupil plane data into a universal representation that provides continuous spectral and angular dependencies, enabling comprehensive material and structural characterization.
3Manufacturing precision
If diffraction-limited optics are used, then the resolution is determined by the diffraction limit, but sub-diffraction structural information cannot be resolved
Solution Approach 1:
The patent overcomes the diffraction limit by inverting the detection approach from image space to frequency space (pupil plane). By measuring the angular spectrum of the scattered light in the pupil plane and performing Fourier transform, the system retrieves sub-diffraction structural information that would be inaccessible to conventional image-plane detection, achieving manufacturing precision beyond the diffraction barrier.
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 structural information extraction with spot sizes less than 10 μm, allowing for simultaneous measurement of a continuous range of wavelengths and angles of incidence, improving the characterization of patterned semiconductor features beyond diffraction limits.
Implementation Method 1
A scanning white-light interferometer uses broadband light that is split to produce a probe beam and a reference beam, which when combined produces an interference pattern
Implementation Method 2
an interferometric objective lens that receives the illumination beam and focuses the illumination beam on the sample
Implementation Method 3
a beam splitter that directs the illumination beam toward the sample and directs the illumination beam through an aperture stop at an objective pupil plane, wherein the illumination beam is reflected by the sample to form a reflected beam
Data Source
AI summary
A white light interferometric metrology device operates in the image plane and objective pupil plane. The interferometric metrology device extracts the electric field with complex parameters and that is a function of azimuth angle, angle of incidence and wavelength from interferometric data obtained from the pupil plane. Characteristics of the sample are determined using the electric field based on an electric field model of the azimuth angle, the angle of incidence and the wavelength that is specific for a zero diffraction order. A center of the pupil in the pupil plane may be determined based on a Fourier transform of the interferometric data at each new measurement and used to convert each pixel from the camera imaging the objective pupil plane into a unique set of angle of incidence and azimuth angle of light incident on the sample.