Metrology Method for Overlay Measurement on Thick Stacks
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Solution Overview
Problem
Current metrology systems face challenges in accurately measuring overlay on thick stacks due to rapid oscillation of stack sensitivity with wavelength, which is exacerbated by the finite bandwidth of measurement radiation, leading to unreliable results.
Innovation Solution
A method and apparatus that estimate narrowband measurement values from wideband measurement values using a processor-controlled system, capable of illuminating targets with wideband radiation and detecting scattered radiation, allowing for improved accuracy in overlay metrology without requiring narrowband radiation sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wideband measurement radiation is used, then measurement speed and signal strength are improved, but measurement precision deteriorates due to rapid oscillation of stack sensitivity with wavelength
Solution Approach 1:
The patent segments the wideband measurement into multiple narrowband measurements by dividing the broadband spectrum into discrete wavelength bands. Each narrowband measurement is performed at a specific wavelength where stack sensitivity is relatively stable, avoiding the rapid oscillations that occur across the entire broadband range. This segmentation allows the system to maintain both speed and precision by processing multiple narrowband measurements simultaneously or sequentially.
Solution Approach 2:
The patent changes the wavelength parameter of the measurement radiation to specific values within the broadband range, selecting wavelengths where stack sensitivity oscillations are minimized or where measurements can be reliably taken. By adjusting the wavelength parameter rather than using a fixed broadband source, the system adapts to the oscillating sensitivity characteristics and maintains measurement accuracy across thick stacks.
2Measurement precision
If narrowband measurement radiation is used, then measurement precision is improved, but device complexity increases due to requirements for narrowband radiation sources
Solution Approach 1:
The patent makes the broadband radiation source universal by enabling it to perform multiple measurement functions across different wavelength bands. Instead of requiring separate narrowband sources for each measurement, the single broadband source is used to perform all necessary narrowband measurements by selectively filtering or modulating the broadband signal. This multi-functionality eliminates the need for complex narrowband radiation sources while maintaining measurement precision.
Solution Approach 2:
The patent creates virtual narrowband measurements by processing and analyzing specific wavelength portions of the broadband signal. Rather than physically generating narrowband radiation, the system copies the characteristics of narrowband measurements by extracting and analyzing specific spectral components from the broadband source, effectively simulating narrowband measurement conditions using a broadband source.
3Adaptability or versatility
If thick stack targets are measured, then overlay measurement capability is extended, but reliability deteriorates due to rapid oscillation of stack sensitivity
Solution Approach 1:
The patent introduces dynamic wavelength selection or modulation to adapt the measurement system to the oscillating stack sensitivity characteristics of thick stacks. By dynamically adjusting the wavelength or combining multiple wavelength measurements, the system can track and compensate for the oscillations in stack sensitivity, maintaining reliable measurements even as the stack thickness increases and sensitivity oscillations become more rapid.
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 enables reliable and accurate overlay measurements on thick stacks using existing metrology hardware, improving measurement precision by modeling wideband data to simulate narrowband conditions, thus overcoming the limitations of current systems.
Implementation Method 1
a detection system configured to detect scattered radiation arising from illumination of the target
Implementation Method 2
measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of reflected angle; or polarization as a function of reflected angle—to obtain a 'spectrum' from which a property of interest of the target can be determined
Data Source
AI summary
Disclosed is a method and associated apparatus of determining a performance parameter (e.g., overlay) of a target on a substrate, and an associated metrology apparatus. The method comprises estimating a set of narrowband measurement values from a set of wideband measurement values relating to the target and determining the performance parameter from said set of narrowband measurement values. The wideband measurement values relate to measurements of the target performed using wideband measurement radiation and may correspond to different central wavelengths. The narrowband measurement values may comprise an estimate of the measurement values which would be obtained from measurement of the target using narrowband measurement radiation having a bandwidth narrower than said wideband measurement radiation.