Single-Pad Overlay Measurement Using Dual-Pitch Moiré Gratings
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Solution Overview
Problem
Current semiconductor manufacturing processes face challenges in accurately measuring and controlling critical dimensions and overlay errors in multi-layer structures due to the limitations of existing lithographic projection apparatuses, particularly when features are smaller than the classical resolution limit, making it difficult to reproduce intended patterns and ensure electrical functionality.
Innovation Solution
A measurement structure comprising a first and second grating at different pitches in separate layers of a multi-layer stack, which generates a Moire interference pattern used to determine parameters of interest, such as overlay offset, by analyzing the interference components formed when illuminated by radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If lithographic projection apparatuses are used to print features smaller than the classical resolution limit, then the critical dimension can be reduced, but the manufacturing precision deteriorates due to difficulty in reproducing intended patterns
Solution Approach 1:
The patent transitions from direct spatial measurement to frequency domain measurement by analyzing Moire interference patterns. The measurement structure uses overlapping gratings with slightly different pitches to generate Moire fringes, where the interference pattern's frequency and phase encode overlay information. This dimensional transformation from real space to frequency space enables precise measurement of sub-resolution features.
Solution Approach 2:
The patent introduces Moire interference patterns as an intermediary measurement mechanism. Instead of directly measuring the overlay between two sub-resolution gratings, the system uses the interference pattern generated by their superposition as a mediator. The Moire fringes amplify the overlay signal into a measurable form, allowing indirect but accurate measurement of alignment errors that would otherwise be below the resolution limit.
2Productivity
If overlay measurement structures are made smaller to fit more devices on a substrate, then the productivity increases, but the measurement precision deteriorates due to reduced signal quality
Solution Approach 1:
The patent measures overlay parameters in the frequency domain rather than directly in spatial domain. By transforming the measurement problem into analyzing the frequency and phase of Moire interference patterns, the system achieves high measurement precision even with compact measurement structures. The Fourier transform of the Moire pattern provides precise overlay information without requiring large physical dimensions.
Solution Approach 2:
The patent changes the measurement approach from direct spatial measurement to frequency-based measurement. By analyzing the spectral characteristics (frequency and phase) of the Moire interference pattern rather than direct spatial positions, the system maintains high measurement precision while using smaller measurement structures that can be densely packed on the substrate.
3Productivity
If the pitch of gratings is reduced to increase device density, then the productivity increases, but the difficulty of detecting and measuring worsens due to sub-resolution features
Solution Approach 1:
The patent uses Moire interference patterns as an intermediary that translates sub-resolution grating overlay information into a detectable form. The interference pattern generated by superimposing two gratings with slightly different pitches creates visible Moire fringes whose frequency and phase encode the overlay error, making measurement of sub-resolution features possible through indirect optical measurement.
Solution Approach 2:
The patent transforms the measurement from direct spatial domain observation to frequency domain analysis. By measuring the frequency and phase of Moire interference patterns rather than directly observing grating positions, the system can accurately measure overlay of sub-resolution gratings that would be undetectable in the spatial domain.
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
Enhances the accuracy of measuring and controlling critical dimensions and overlay errors, allowing for improved process monitoring and correction in semiconductor manufacturing, thereby ensuring consistent pattern reproduction and device performance.
Implementation Method 1
when illuminated by incident radiation, scattered radiation from the measurement structure forms an interference pattern at a detector, wherein the interference pattern comprises at least a first Moire interference component and a second Moire interference component
Implementation Method 2
when illuminated by incident radiation, scattered radiation from the measurement structure forms an interference pattern at a detector
Data Source
AI summary
A structure including a first grating at a first pitch in a first layer of a multi-layer stack structure; and a second grating at a second pitch in a second layer of the multi-layer stack structure, wherein, when illuminated by incident radiation, scattered radiation from the measurement structure forms an interference pattern at a detector, wherein the interference pattern includes at least a first Moire interference component and a second Moire interference component. A method for measuring a parameter of interest in a manufacturing process based on the measurement structure, which includes obtaining an interference pattern for the measurement structure, identifying a first Moire interference component and identifying a second Moire interference component in the interference pattern; and determining the measurement of a parameter of interest based on the first Moire interference component and the second Moire interference component.