Lithographic Level Sensor Using Variable Wavelength Interferometry
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Solution Overview
Problem
Current level sensors in lithographic apparatuses face challenges in accurately measuring the position of reflective surfaces on substrates due to interference effects from underlying layers, leading to errors and the need for costly safety measures to prevent machine safety issues.
Innovation Solution
A method and arrangement using a variable broadband radiation source to split beams into measurement and reference paths, detecting interference patterns with varying component wavelengths and intensity levels, allowing for precise determination of reflective surface positions by resolving overlapping peaks and reducing apparent surface depression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a level sensor uses a fixed wavelength radiation source to measure substrate surfaces, then the measurement process is simple and fast, but measurement precision deteriorates due to interference effects from underlying layers causing overlapping peaks and apparent surface depression
Solution Approach 1:
The patent applies dynamics by making the radiation source wavelength variable rather than fixed. The level sensor dynamically changes the wavelength of radiation across a broad spectrum range, allowing the measurement system to adapt to different layer structures and resolve interference patterns by observing how peaks shift with wavelength changes.
Solution Approach 2:
The patent changes the wavelength parameter of the radiation source across a broad spectrum. By varying the wavelength and measuring how interference peaks shift, the system can distinguish between peaks from different layers, thereby resolving the apparent surface depression problem and improving measurement precision.
2Productivity
If a level sensor operates at a larger working distance for parallel wafer measurement, then productivity improves and safety increases, but measurement precision deteriorates due to reduced signal intensity and increased apparent surface depression
Solution Approach 1:
The system dynamically adjusts the wavelength across a broad spectrum to compensate for the reduced signal intensity at larger working distances. By utilizing multiple wavelengths and analyzing peak shifts, the system maintains measurement precision even when operating at distances that enable parallel wafer measurement and improved safety.
Solution Approach 2:
The patent utilizes parameter changes in wavelength to enhance measurement capability at larger working distances. The broad spectral range allows the system to find optimal wavelengths that provide sufficient signal intensity and resolution even when the sensor is positioned farther from the substrate, thereby maintaining precision while improving productivity.
3Measurement precision
If a level sensor uses broadband radiation with varying wavelengths to resolve interference patterns, then measurement precision improves by resolving overlapping peaks, but device complexity increases due to the need for variable wavelength sources and complex data processing
Solution Approach 1:
The patent employs a tunable broadband radiation source that can dynamically adjust its wavelength output. This dynamic capability allows the system to sweep through different wavelengths and observe peak shifts, enabling resolution of overlapping interference patterns from multiple layers without requiring overly complex hardware architectures.
Solution Approach 2:
By changing the wavelength parameter across a broad spectrum, the system exploits the physical phenomenon of peak shifting to distinguish between interference patterns from different layers. This approach achieves high measurement precision through relatively straightforward spectral analysis compared to more complex spatial or temporal measurement methods.
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 provides accurate and efficient measurement of substrate surfaces with reduced apparent surface depression, enabling higher precision and safety while decreasing manufacturing costs by allowing parallel wafer measurement at a larger working distance.
Implementation Method 1
splitting a broadband source beam of radiation into a measurement beam directed along a first path, and a reference beam directed along a second path
Implementation Method 2
combining the reflected measurement beam and the reflected reference beam; and detecting an interference pattern of the combined beams
Data Source
AI summary
Disclosed is a method of measuring a position of at least one substantially reflective layer surface on a substrate in a lithographic apparatus, and associated level sensor and lithographic apparatuses. The method comprises performing at least two interferometrical measurements using a broadband light source. Between each measurement, the component wavelengths and/or intensity levels over the component wavelengths of the broadband source beam is varied such that, where it is only the intensity levels that are varied, the intensity variation is different for at least some of the beam's component wavelengths. Alternatively, a single measurement and subsequent processing of the measurement to obtain measurement data whereby the component wavelengths and/or intensity levels over the component wavelengths are different can be applied as well to obtain the position.