Photomask Critical Dimension Mapping via DUV Scatterometry
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Solution Overview
Problem
Current methods for determining line-width size distributions on photomasks are limited by low accuracy and speed, particularly due to the small dynamic range of detection devices and the need for destructive or slow measurement techniques, which restricts the ability to detect sub-nanometer variations in critical dimensions essential for semiconductor manufacturing.
Innovation Solution
A non-imaging optical system measures Deep-Ultra-Violet (DUV) transmission across photomasks, allowing for fast and non-destructive determination of critical dimension distributions by transforming transmission variations into CD distributions using a linear ratio, enabling accurate mapping without removing the pellicle and with measurement times under one second.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical image processing inspection tools are used to measure CD distribution on photomasks, then measurement can be performed non-destructively, but measurement precision is limited to about 1 nm due to small dynamic range of detection devices
Solution Approach 1:
The patent replaces direct optical image processing with a scatterometry-based optical metrology system that measures scattered light intensity and angle distributions. This substitution enables non-destructive measurement while achieving sub-nanometer precision by analyzing the angular distribution of scattered light rather than relying on direct imaging with limited dynamic range detectors
Solution Approach 2:
The patent transforms the measurement parameter from direct intensity measurement (limited dynamic range) to angular distribution measurement of scattered light. By measuring the angular distribution of scattered light at multiple angles and wavelengths, the system achieves enhanced precision in CD determination while maintaining non-destructive measurement capability
2Measurement precision
If scatterometry techniques are used to measure CD distributions on photomasks, then measurement precision can reach about 1 nm, but measurement speed is slow and requires predefined geometrical features on scribe-lines
Solution Approach 1:
The patent extends scatterometry measurement capability from predefined scribe-line features to arbitrary pattern geometries across the entire photomask. The system can measure CD distributions on any pattern type (contact holes, trenches, lines, curves) without requiring predefined geometrical features, thereby enabling full-mask mapping while maintaining sub-nanometer precision
Solution Approach 2:
The patent implements a calibration procedure that establishes the relationship between scattered light parameters and CD values before actual measurement. This preliminary calibration enables rapid measurement of arbitrary patterns without requiring complex simulation algorithms during the measurement phase, significantly improving measurement speed while maintaining precision
3Measurement precision
If scanning electron microscope is used to measure CD on photomasks, then measurement precision can reach about 1 nm, but the method is destructive and measurement speed is slow
Solution Approach 1:
The patent replaces electron beam-based SEM measurement with optical scatterometry measurement using photons in the DUV range. This substitution eliminates the destructive electron beam interaction with the photomask pattern while achieving comparable or better measurement precision through analysis of scattered light angular distributions
4Measurement precision
If atomic-force microscope is used to measure CD distributions on photomasks, then measurement precision is sufficient, but measurement speed is extremely slow (tens of minutes per point)
Solution Approach 1:
The patent replaces mechanical AFM scanning with optical scatterometry measurement. This substitution eliminates the extremely slow mechanical scanning process while maintaining sufficient measurement precision by analyzing the angular distribution of scattered light, enabling full-mask mapping in minutes rather than hours
Solution Approach 2:
The patent implements rapid periodic measurement cycles using pulsed DUV illumination and fast detectors to capture scattered light angular distributions. This periodic measurement approach enables high-speed data acquisition across multiple points on the photomask while maintaining the precision needed for CD distribution mapping
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 provides high accuracy (less than 0.1% transmission level) and speed, enabling efficient mapping of full-size photomasks with improved precision and throughput, overcoming the limitations of existing methods by using a wideband DUV optical measurement system and fast detection devices.
Implementation Method 1
measuring deep Ultra-Violet (DUV) transmission across the photomask
Data Source
AI summary
In general, in one aspect, a method includes determining a critical dimension (CD) distribution on a photomask by measuring deep Ultra-Violet (DUV) transmission across the photomask.