Photolithographic Mask Critical Dimension Variation Analysis
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Solution Overview
Problem
Current methods for determining critical dimension variation (CDU) in photolithographic masks are inefficient, requiring complex and costly equipment like SEM and AFM, and are not suitable for mapping CD variations across the entire mask due to limitations in resolution and time consumption, especially as masks degrade during operation.
Innovation Solution
A method using layout data to identify sub-areas on the mask, measuring optical transmission within these areas, determining sub-area specific constants, and combining these to calculate CD variations without the need for additional equipment like SEM or AFM, allowing for faster and more cost-effective CDU analysis across the mask.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SEM or AFM tools are used to measure CD variation, then measurement precision is improved, but device complexity and time consumption increase significantly
Solution Approach 1:
The patent replaces complex mechanical measurement systems (SEM, AFM) with a simplified optical measurement system that uses light transmission through the mask. This substitution maintains measurement capability while dramatically reducing equipment complexity and measurement time by using optical properties rather than mechanical scanning or electron beam methods.
Solution Approach 2:
The patent creates an optical copy or representation of the mask's CD characteristics by measuring light transmission patterns. Instead of directly measuring physical dimensions with complex equipment, the system captures optical transmission data that replicates the CD variation information, enabling indirect but accurate measurement through simpler means.
2Measurement precision
If SEM or AFM scanning is performed across the mask, then CD variation mapping is improved, but productivity decreases due to time consumption
Solution Approach 1:
The patent employs periodic or systematic scanning of light across the mask area, measuring transmission at multiple predetermined positions in a structured sequence. This periodic measurement approach enables comprehensive mapping of CD variations across the entire mask while maintaining high speed, replacing the slow sequential scanning of traditional methods with parallel optical measurements.
Solution Approach 2:
The patent measures transmission at multiple positions across the mask, potentially exceeding the minimum required measurements. By taking more measurements than strictly necessary (excessive action), the system ensures comprehensive coverage and accurate mapping of CD variations while maintaining high productivity through the efficiency of optical measurement at each position.
3Ease of operation
If pellicle is removed for CD measurements, then measurement access is improved, but reliability decreases due to uncertainty from re-mounting
Solution Approach 1:
The patent enables measurements to be performed on the mask in its normal operational state with the pellicle attached. The measurement system is designed to work through or alongside the pellicle structure, allowing the mask to serve itself for measurement purposes without requiring external intervention to remove protective components, thereby maintaining both accessibility and reliability.
4Measurement precision
If high energy electrons from SEM are used for measurement, then measurement capability is improved, but mask performance deteriorates
Solution Approach 1:
The patent replaces the harmful high-energy electron beam of SEM with harmless optical radiation (light) for measurement purposes. This substitution eliminates the damaging effect on the mask while maintaining the ability to achieve high measurement precision through optical transmission measurements, avoiding the trade-off between measurement capability and mask integrity.
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 method provides a fast and cost-effective way to analyze CDU across photolithographic masks, reducing the need for complex measurements and extending the operational lifetime of masks by enabling regular CDU control and correction, thus improving yield and reducing yield loss.
Implementation Method 1
measuring a distribution of a transmission of each sub-area
Data Source
AI summary
The invention relates to a method for determining a critical dimension variation of a photolithographic mask which comprises (a) using layout data of the photolithographic mask to determine at least two sub-areas of the photolithographic mask, each sub-area comprising a group of features, (b) measuring a distribution of a transmission of each sub-area, (c) determining a deviation of the transmission from a mean transmission value for each sub-area, (d) determining a constant specific for each sub-area, and (e) determining the critical dimension variation of the photolithographic mask by combining for each sub-area the deviation of the transmission and the sub-area specific constant.