Wavelength Combining of Multiple Light Sources
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Solution Overview
Problem
Current alignment system illumination systems in lithographic apparatuses face challenges in efficiently providing a range of ultraviolet (UV) wavelengths, which is necessary for accurate substrate positioning and metrology in lithographic operations.
Innovation Solution
A light combiner system utilizing multiple light sources with specific filters that reflect and transmit light from different sources, optimizing the angle of incidence to enhance light combination efficiency and reduce polarization splitting, allowing for a broader UV spectrum coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple UV light sources are combined to provide a range of wavelengths, then the wavelength coverage and metrology performance are improved, but the system complexity and difficulty of combining sources increase
Solution Approach 1:
The illumination system is segmented into multiple independent light sources, each emitting at a specific UV wavelength. This allows the system to cover a broader wavelength range by combining discrete sources rather than using a single broadband source, thereby improving wavelength coverage while maintaining manageable system complexity through modular design
Solution Approach 2:
The illumination system is designed to perform multiple functions using a single integrated structure. The same optical train and illumination optics are used for all multiple light sources, allowing the system to provide wavelength-tunable illumination for different metrology applications without requiring separate optical paths for each wavelength
2Productivity
If filters are used to combine multiple light sources, then wavelength selection and combination efficiency are improved, but polarization splitting and optical losses occur
Solution Approach 1:
Dichroic mirrors are used as intermediary optical elements to combine multiple light sources. These mirrors are designed to reflect specific UV wavelengths while transmitting others, enabling efficient wavelength selection and combination. The intermediary filters minimize optical losses by being optimized for high reflectivity and transmissivity in their respective wavelength bands, thereby maintaining high light combination efficiency
3Measurement precision
If the angle of incidence is increased for filter optimization, then wavelength separation is improved, but polarization splitting increases
Solution Approach 1:
The angle of incidence for the dichroic mirrors is optimized to a specific value that balances wavelength separation performance with polarization effects. By carefully selecting and adjusting this geometric parameter, the system achieves sufficient wavelength separation for effective source combination while minimizing polarization splitting that could degrade illumination quality and metrology measurements
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 solution enables improved alignment and metrology by efficiently combining UV light sources, providing a more accurate and stable range of wavelengths for precise substrate positioning and height measurement, thereby enhancing the overall performance of lithographic processes.
Implementation Method 1
The first filter is designed to substantially reflect light generated from a first source of the plurality of light sources
Implementation Method 2
to substantially transmit light generated from a second source of the plurality of light sources
Implementation Method 3
The second filter is designed to substantially reflect light generated from the first source and the second source of the plurality of light sources
Implementation Method 4
to substantially transmit light generated from a third source of the plurality of light sources
Data Source
AI summary
A light combiner (500) for use in a metrology tool includes a plurality of light sources (LED 1, LED 2, LED 3, LED 4, LED 5), a first filter (502), and a second filter (504). The first filter is designed to substantially reflect light generated from a first source of the plurality of light sources, and to substantially transmit light generated from a second source of the plurality of light sources. The second filter is designed to substantially reflect light generated from the first source and the second source of the plurality of light sources, and to substantially transmit light generated from a third source of the plurality of light sources. An angle of incidence of the light generated from the first source on a surface of the first filter is less than 30 degrees.