Motorized Spatial Filter for Target Mark Asymmetry Measurement
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Solution Overview
Problem
Current metrology apparatuses face challenges in accurately measuring target mark asymmetry across multiple wavelengths, which affects capture speed and precision in lithographic processes.
Innovation Solution
A system comprising an imaging system, a spatial filter with obscurations having an angular dependent radius that varies azimuthally, and a detector to receive and measure the intensity of desired diffraction orders, allowing for the blocking of undesired diffraction orders and improved measurement of target mark asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spatial filter blocks all high-order diffraction orders, then measurement precision of target mark asymmetry is improved, but capture speed decreases due to loss of useful diffraction information
Solution Approach 1:
The spatial filter applies selective blocking rather than uniform filtering - it blocks high-order diffraction orders in specific angular regions while preserving useful diffraction information in other regions. This local differentiation allows the system to improve measurement precision for target mark asymmetry while maintaining capture speed by retaining beneficial diffraction orders.
Solution Approach 2:
The spatial filter configuration is dynamically adjusted based on the specific measurement requirements. By adapting which diffraction orders are blocked versus preserved, the system can optimize between measurement precision and capture speed depending on the measurement context, rather than using a fixed filtering approach.
2Ease of manufacture
If a spatial filter uses fixed circular obscurations, then manufacturing simplicity is maintained, but measurement accuracy of target mark asymmetry deteriorates due to insufficient angular discrimination
Solution Approach 1:
The spatial filter transitions from symmetric circular obscurations to asymmetric sector-shaped or angularly-dependent obscurations. This asymmetric geometry provides superior angular discrimination capability, enabling more accurate measurement of target mark asymmetry while remaining manufacturable through standard photolithographic processes.
Solution Approach 2:
The obscuration geometry extends from simple radial dimensions to include angular dependencies. By defining obscurations that vary in both radial and angular dimensions (e.g., sector shapes with specific angular spans), the filter achieves enhanced angular discrimination without significantly increasing manufacturing complexity.
3Adaptability or versatility
If all diffraction orders are captured for multi-wavelength measurements, then wavelength versatility is improved, but measurement precision of target mark asymmetry deteriorates due to contamination from undesired diffraction orders
Solution Approach 1:
The diffraction order spectrum is segmented into desired and undesired regions. The spatial filter selectively blocks undesired high-order diffraction orders while preserving desired lower-order diffraction orders across multiple wavelengths. This segmentation allows the system to maintain wavelength versatility while improving measurement precision by eliminating contaminating diffraction orders.
Solution Approach 2:
The spatial filter converts the potentially harmful effect of overlapping diffraction orders from multiple wavelengths into a benefit by selectively blocking only the harmful high-order overlaps while preserving the useful lower-order signals. This allows multi-wavelength measurements to proceed with improved precision.
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
The system enhances the capture speed and accuracy of target mark asymmetry measurements across various wavelengths, improving the overall precision and efficiency of lithographic processes.
Implementation Method 1
A fast and non-invasive form of a specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Implementation Method 2
The detector is configured to receive and measure an intensity of the one or more desired diffraction orders
Data Source
AI summary
A system includes an imaging system, a spatial filter, and a detector. The system is configured to receive a plurality of diffraction orders. The spatial filter is configured to block one or more undesired diffraction orders of the plurality of diffraction orders and to pass one or more desired diffraction orders of the plurality of diffraction orders. The spatial filter includes one or more obscurations having an angular dependent radius that varies azimuthally. The detector is configured to receive and measure an intensity of the one or more desired diffraction orders. The spatial filter is motorized.