Tunable Acoustic Gradient Lens for Imaging Ellipsometer Depth Scanning
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Solution Overview
Problem
Conventional imaging ellipsometer systems face challenges with speed, repeatability, and accuracy due to motorized focusing mechanisms and rotating optical components, which can lead to beam walking and reduced precision in measurements, especially for precision metrology applications requiring high spatial resolution.
Innovation Solution
The implementation of a tunable acoustic gradient index (TAG) lens that modulates the focus position at a resonant frequency, eliminating the need for mechanical translation and integrating polarizers onto the camera sensor to enhance focus accuracy and speed, thereby reducing the time required for depth scanning and improving measurement precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If motorized focusing mechanisms are used to achieve focus across the entire image field, then measurement coverage is improved, but measurement time increases and repeatability deteriorates
Solution Approach 1:
The patent replaces motorized focusing mechanisms with a fixed-focus optical design that uses a carefully selected focal length to achieve adequate focus across the entire inclined image field without mechanical translation. This substitution eliminates the time-consuming scanning process while maintaining full field coverage.
Solution Approach 2:
The patent employs dynamic range compression techniques and computational imaging methods to achieve extended depth of field without mechanical focusing. By using software-based refocusing and image processing, the system maintains focus across the entire field of view while eliminating the need for time-consuming mechanical scans.
2Measurement precision
If motorized focusing mechanisms are used to scan through depth, then focus accuracy across the field is improved, but repeatability and precision deteriorate due to mechanical translation
Solution Approach 1:
The patent eliminates mechanical translation by using a fixed-focus optical system with carefully selected focal length and aperture settings. This mechanical-free approach removes the sources of repeatability errors while maintaining adequate focus accuracy across the entire image field through optical design and computational methods.
Solution Approach 2:
The patent uses computational imaging techniques including dynamic range compression and software-based refocusing to achieve extended depth of field. These digital methods provide repeatable, precise focus control without the mechanical errors inherent in motorized focusing systems.
3Adaptability or versatility
If rotating optical components are used to control polarization state, then measurement capability is improved, but beam walking occurs reducing precision
Solution Approach 1:
The patent extracts and removes rotating optical components from the system. By using fixed polarizing elements and alternative measurement approaches, the system eliminates beam walking while retaining the necessary polarization control capability for ellipsometric measurements.
Solution Approach 2:
The patent uses fixed optical components with carefully controlled orientations to achieve the same measurement objectives as rotating components would provide. By using fixed elements with predetermined angles, the system achieves polarization control without the beam position instability caused by rotation.
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
The TAG lens enables fast depth scanning and improves repeatability and accuracy by maintaining focus across the entire image field without mechanical translation, reducing measurement time and minimizing the effects of beam walking, thus enhancing the precision and reliability of ellipsometric measurements.
Implementation Method 1
tunable acoustic gradient index of refraction (TAG) lens... The TAG lens is controlled to provide a modulation of a focus position of the imaging ellipsometer system at or near a resonant frequency of operation of the TAG lens
Implementation Method 2
The polarizer is located along the illumination path and is configured to polarize the source light that is directed toward the workpiece
Implementation Method 3
the reflected light is analyzed to determine the magnitude and phase of light reflected by the two constituent, orthogonal polarizations (s- and p-)
Implementation Method 4
lens configuration including a tunable acoustic gradient index of refraction (TAG) lens... located along the imaging optical path
Data Source
AI summary
A imaging ellipsometer system is provided including a lens configuration with tunable acoustic gradient index of refraction (“TAG”) lens. The imaging ellipsometer system further includes a light source, a polarizer, a compensator, an analyzer and a camera. Light from the light source passes through the polarizer and is directed toward a workpiece. In various implementations, the compensator is located and configured to elliptically polarize the light either before or after the light is reflected from the workpiece. The lens configuration receives the reflected workpiece light and the TAG lens is controlled to provide a modulation of a focus position. The camera receives workpiece light that passes through the TAG lens and the analyzer during an image exposure and provides a corresponding camera image. An ellipsometry analysis is performed (e.g., to determine at least one of a refraction index, or a thickness of one or more layers of the workpiece, etc.)