Angularly Resolved Scatterometer Acousto-Optic Tunable Filter
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Solution Overview
Problem
Current inspection devices for lithographic processes face challenges in efficiently measuring parameters at multiple wavelengths due to the need for expensive optical multiplexing and alignment issues with multiple laser sources, as well as time-consuming filter swapping for different wavelength measurements.
Innovation Solution
An angularly resolved scatterometer utilizing a broadband radiation source and an acousto-optical tunable filter with a high-NA objective lens and driver circuit to select and control the wavelength range of the radiation beam, allowing for rapid and efficient measurements at multiple wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple laser sources are used to provide different wavelengths, then measurement capability at multiple wavelengths is improved, but device complexity and cost increase due to expensive optical multiplexing and alignment requirements
Solution Approach 1:
The patent replaces the mechanical/optical system of multiple laser sources with acoustic waves to control wavelength selection. An acousto-optical tunable filter uses sound waves (acoustic field) instead of mechanical laser alignment and optical multiplexing to select different wavelengths from a single broadband source, thereby reducing device complexity while maintaining multi-wavelength measurement capability.
Solution Approach 2:
The patent introduces an acousto-optical tunable filter as an intermediary device between the broadband radiation source and the sample. This filter uses acoustic waves as a mediator to select specific wavelengths from the broadband source, eliminating the need for direct mechanical alignment of multiple laser sources and reducing optical complexity.
2Adaptability or versatility
If filters are swapped into and out of the inspection beam for different wavelength measurements, then measurement versatility is improved, but productivity decreases due to time-consuming filter swapping
Solution Approach 1:
The patent employs a dynamic acousto-optical tunable filter that can rapidly switch between different wavelengths by changing the acoustic frequency, rather than physically swapping static filters. This dynamic control allows for fast wavelength switching without mechanical movement, thereby maintaining measurement versatility while significantly improving inspection throughput and productivity.
Solution Approach 2:
The patent replaces the mechanical filter swapping process with an acoustic field-based wavelength selection mechanism. By using acoustic waves to modulate the optical properties of the crystal, the system achieves rapid wavelength changes without any physical movement or mechanical intervention, thereby eliminating the throughput bottleneck associated with filter swapping.
3Device complexity
If a broadband radiation source is used, then device complexity is reduced by eliminating multiple laser sources, but measurement precision may worsen due to wavelength-dependent optical properties of substrate layers
Solution Approach 1:
The patent uses an acousto-optical tunable filter as an intermediary to select specific narrow wavelength bands from the broadband source. This filter acts as a wavelength-selective gate that isolates the desired wavelength range, thereby maintaining measurement precision comparable to using a monochromatic source while retaining the simplicity of a single broadband source.
Solution Approach 2:
The patent applies the principle of local quality by selecting a specific narrow wavelength range from the broadband source at each measurement point. Rather than using the entire broadband spectrum simultaneously, the system locally selects the appropriate wavelength band needed for the specific measurement, thereby maintaining precision while using a simple broadband source.
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 solution enables fast and accurate measurements at various wavelengths without the need for expensive multiplexing devices and reduces measurement time, improving the throughput of inspection devices.
Implementation Method 1
an acousto-optical tunable filter including an acousto-optical crystal arranged to receive the first beam of radiation, a transducer coupled to the acousto-optical filter and arranged to excite acoustic waves therein
Implementation Method 2
measure the intensity of the scattered radiation as a function of angle
Data Source
AI summary
An angularly resolved scatterometer uses a broadband radiation source and an acousto-optical tunable filter to select one or more narrowband components from the broadband beam emitted by the source for use in measurements. A feedback loop can be used to control the intensity of the selected narrowband components to reduce noise.