Multiplexed Metrology Apparatus for Substrate Signal Noise Reduction
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Solution Overview
Problem
Current metrology apparatuses face challenges in accurately measuring characteristics of structures on substrates due to dominant detector noise, especially in infrared applications, which affects the signal-to-noise ratio and requires costly cooling methods to reduce noise, and existing multi-wavelength measurements are sequential, increasing complexity and cost.
Innovation Solution
A method and apparatus that perform multiplexed measurements using a plurality of wavelengths, where each measurement acquisition uses a different subset of wavelengths, and the signals are de-multiplexed to obtain separated signals for each wavelength, improving the signal-to-noise ratio by reducing additive sensor noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple wavelengths are used to improve metrology accuracy, then measurement precision is improved, but device complexity increases due to sequential measurements
Solution Approach 1:
The patent combines multiple wavelength measurements into a single simultaneous measurement process. The illumination source emits multiple wavelengths at the same time, and the detector captures all wavelength components in one measurement acquisition, eliminating the need for sequential measurements and reducing system complexity.
Solution Approach 2:
The detector is designed to simultaneously detect multiple wavelengths, making it a multi-functional device that can handle the entire spectral range in a single operation. This universal detection capability eliminates the need for multiple specialized detectors or wavelength-specific measurement setups.
2Measurement precision
If detector cooling is applied to reduce noise, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent converts the harmful effect of detector noise into a manageable parameter by using signal processing techniques. Instead of trying to eliminate noise through physical cooling, the system processes the noisy signals computationally to extract accurate measurements, thereby avoiding complex cooling infrastructure.
Solution Approach 2:
The patent replaces the mechanical/thermal cooling system with a computational signal processing approach. By using algorithms to filter and process the multiplexed signals, the system achieves noise reduction without requiring physical cooling mechanisms, thereby simplifying the device architecture.
3Measurement precision
If sequential multi-wavelength measurements are performed, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent implements continuous multi-wavelength illumination and simultaneous detection, ensuring that all wavelength measurements occur continuously in parallel rather than sequentially. This continuous action maintains measurement precision while dramatically reducing the total time required for overlay measurements.
4Measurement precision
If multiple detectors are used to capture different wavelengths, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs a universal detector that can simultaneously sense multiple wavelengths, eliminating the need for multiple specialized detectors. This single multi-functional detector reduces system complexity while maintaining the ability to perform wavelength-specific measurements through signal processing.
Solution Approach 2:
The patent merges the functionality of multiple wavelength-specific detectors into a single detector that captures all wavelength components simultaneously. This consolidation reduces the number of components, simplifies the optical path, and lowers system cost while preserving measurement capabilities.
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 enhances the signal-to-noise ratio by increasing the signal while maintaining the same number of sensor noise introductions, reducing error variance, and improving measurement accuracy without the need for extensive cooling, thus simplifying and cost-reducing the measurement process.
Implementation Method 1
a detector for detecting a plurality of multiplexed measurement signals following scattering by the structure
Data Source
AI summary
Disclosed is a method and associated inspection apparatus for measuring a characteristic of interest relating to a structure on a substrate. The inspection apparatus uses measurement radiation comprising a plurality of wavelengths. The method comprises performing a plurality of measurement acquisitions of said structure, each measurement acquisition being performed using measurement radiation comprising a different subset of the plurality of wavelengths, to obtain a plurality of multiplexed measurement signals. The plurality of multiplexed measurement signals are subsequently de-multiplexed into signal components according to each of said plurality of wavelengths, to obtain a plurality of de-multiplexed measurement signals which are separated according to wavelength.