Acousto-Optic Device Etendue Expansion for Wafer Inspection
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Solution Overview
Problem
Current semiconductor wafer inspection systems face limitations in etendue and energy efficiency due to the use of traveling lens acousto-optic devices, which result in reduced numerical aperture and field of view, hindering high-throughput and high-resolution imaging.
Innovation Solution
The system employs an acousto-optic device with a controlled illuminated region and an etendue expanding optical module, including a Dammann grating and lenses, to convert collimated input beams into collimated output beams that scan the substrate with increased angular range and energy efficiency, forming spaced apart spots for improved inspection capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traveling lens acousto-optic device is used to focus the input beam, then the beam can be focused to generate flying spot beams, but the energy usage efficiency is reduced and the etendue is reduced
Solution Approach 1:
The patent divides the single acousto-optic device into multiple virtual sub-devices by applying multiple RF signals with different frequencies and phases. This creates multiple independent beam control channels, allowing precise focusing at multiple locations simultaneously while distributing the energy usage across segmented control regions, thereby improving both focusing precision and energy efficiency.
Solution Approach 2:
The patent introduces temporal dimension by using phase-modulated RF signals to create time-varying acoustic fields. This allows the system to achieve spatial focusing precision through temporal phase control, where the phase of RF signals is modulated to dynamically focus beams at different positions, resolving the contradiction between precision and energy efficiency.
2Area of stationary object
If the illuminated area of the acousto-optic device is increased to improve field of view, then the field of view increases, but the etendue is reduced
Solution Approach 1:
The patent applies different RF signal parameters (frequency, phase, amplitude) to different spatial regions of the acousto-optic device. This creates locally optimized beam control where each region is tailored for its specific function, allowing the system to maintain high etendue while achieving wide field of view through localized beam steering and focusing operations.
3Measurement precision
If shorter wavelengths and higher numerical aperture optics are used to achieve high resolution imaging, then the imaging resolution improves, but the system complexity increases
Solution Approach 1:
The patent replaces complex mechanical optical systems with acousto-optic field control. Instead of using multiple physical lenses and mirrors to achieve high numerical aperture, the system uses acoustic field modulation to achieve beam focusing and steering, thereby achieving high imaging resolution while reducing mechanical system complexity.
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 configuration enhances the etendue and throughput of the inspection system, achieving better energy efficiency and enabling higher numerical aperture and field of view, thus supporting high-resolution and high-speed imaging for semiconductor wafer inspection.
Implementation Method 1
illuminating an illuminated region of a surface of an active region of an acousto-optic device with a collimated input beam while feeding the acousto-optic device with a control signal that causes the illuminated region to output illuminated region output beams that are collimated and exhibit deflection angles
Implementation Method 2
The etendue expanding optical module may include a Dammann grating
Data Source
AI summary
A method and a system for illuminating a substrate, the system may include an acousto-optic device (AOD); and an etendue expanding optical module. The AOD may include a surface having an illuminated region; wherein the illuminated region is configured to receive a collimated input beam while being fed with a control signal that causes the illuminated region to output illuminated region output beams that are collimated and exhibit deflection angles that scan, during a scan period, a deflection angular range. The etendue expanding optical module is configured to convert the illuminated region output beams to collimated output beams that impinge on an output aperture; wherein a collimated output beam has a width that exceeds a width of an illuminated region output beam; and wherein the etendue expanding optical module comprises a Dammann grating that is configured to output diffraction patterns, each diffraction pattern comprises diffraction orders that cover a continuous angular range.