Phase-Based Metrology for Overlay Precision
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Solution Overview
Problem
Current metrology techniques, such as scatterometry, face challenges in accurately measuring overlay sensitivity due to the swing curve's wavelength dependence, leading to insensitivity at certain wavelengths and variability across different stacks, making it difficult to ensure sufficient overlay sensitivity and precision in lithographic processes.
Innovation Solution
A method and apparatus that measure a characteristic of a substrate by calculating the effect of the characteristic on the phase of illuminating radiation after scattering, allowing for direct determination of overlay from phase-sensitive measurements, thereby overcoming the limitations of wavelength dependence and stack variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If scatterometry is used to measure overlay, then measurement capability is provided, but measurement precision deteriorates at certain wavelengths due to the swing curve effect
Solution Approach 1:
The patent changes the measurement parameter from intensity-based detection to phase-based detection. By measuring the phase of scattered radiation rather than its intensity, the method eliminates sensitivity to the swing curve effect, maintaining consistent overlay measurement precision across all wavelengths including those where traditional scatterometry fails.
2Reliability
If traditional scatterometry is used, then overlay measurement is possible, but measurement reliability varies considerably across different stacks
Solution Approach 1:
The patent transitions from measuring intensity parameters to measuring phase parameters of scattered radiation. This parameter change makes the measurement independent of stack-specific optical properties, providing consistent reliability across different stacks and eliminating the need for careful wavelength selection and stack-specific optimization.
3Measurement precision
If intensity-based scatterometry is used, then measurement simplicity is maintained, but measurement precision is limited by the swing curve
Solution Approach 1:
The patent measures the phase parameter of scattered radiation instead of intensity. While phase measurement requires additional capabilities, it provides superior precision by eliminating the swing curve limitation, and the phase information can be extracted from scattered radiation using established interferometric techniques.
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 accurate overlay measurement at all wavelengths, improving sensitivity and precision, and eliminating the swing curve's impact, allowing for more reliable process control in lithographic applications.
Implementation Method 1
calculating a value for the characteristic of interest directly from the effect of the characteristic of interest on at least the phase of illuminating radiation when scattered by the structure
Data Source
AI summary
Disclosed is a method and associated apparatus for measuring a characteristic of interest relating to a structure on a substrate. The method comprises calculating a value for the characteristic of interest directly from the effect of the characteristic of interest on at least the phase of illuminating radiation when scattered by the structure, subsequent to illuminating said structure with said illuminating radiation.