Lithography Pattern Verification via Sectorized Surface Area
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Solution Overview
Problem
Current methods for verifying printed patterns on semiconductor devices using lithographic masks are inadequate, particularly for features with complex geometries, as they fail to accurately measure critical dimensions and process windows, leading to unreliable print quality, especially at sub-32nm nodes.
Innovation Solution
A method that involves sectorizing the printed and reference patterns to calculate surface area-based parameters, such as Line-end Area Contour Ratio (LECR), Corner Area Contour Ratio (CCR), and Space Area Contour Ratio (SCR), which provide a more accurate assessment of print quality and process windows by comparing the surface areas of defined regions in the printed and reference patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CD-SEM measurement technique is used to measure critical dimensions, then specific feature types such as regular line/space widths can be measured, but complex geometry features and critical positions such as corners and line-ends cannot be measured
Solution Approach 1:
The verification method segments the pattern into different feature types (line-end, corner, space, bridge features) and applies specific measurement approaches to each segment. This allows the system to measure complex geometries by breaking them down into measurable components rather than attempting to measure them as a whole
Solution Approach 2:
The invention introduces contour extraction and parameter calculation as intermediary steps between the CD-SEM measurement and the final verification. By extracting contours and calculating parameters like LECR, CCR, LCR, and SCR, the system bridges the gap between what CD-SEM can directly measure and the comprehensive verification needed for complex features
2Reliability
If contour-based parameters are determined as a function of focus and dose with best fitting polynomial, then process window can be estimated, but measured values deviate from best fitting polynomial in an important way
Solution Approach 1:
The invention segments the pattern into different feature types and calculates specific parameters for each type. This segmentation allows the system to capture the nuanced behavior of different feature types under varying focus and dose conditions, rather than using a single polynomial fit for all features
Solution Approach 2:
The invention changes the parameters being measured from traditional CD and EPE to area-based parameters (LECR, CCR, LCR, SCR) that better capture the actual print deviations. These parameter changes enable more accurate modeling of the relationship between focus/dose and print quality
3Productivity
If traditional verification methods are used for printed patterns, then manufacturing process can be maintained, but print quality assessment is unreliable especially at sub-32nm nodes
Solution Approach 1:
The invention creates a virtual reference pattern that represents the ideal print outcome, then compares the actual measured pattern against this reference. This copying approach allows verification without changing the physical manufacturing process, maintaining productivity while improving precision
Solution Approach 2:
The invention introduces new area-based parameters (LECR, CCR, LCR, SCR) that are specifically suited for sub-32nm node verification. These parameter changes enable reliable print quality assessment at advanced nodes while maintaining compatibility with existing manufacturing processes
Data Source
Figure 1~2
Figure 3a~3c
Figure 4~6b
AI summary
The invention is related to a method for verifying a printed pattern comprising polygon-shaped features (1-7) as printed by a lithographic tool using a lithographic mask, wherein a number of sectors of features of the pattern are first defined, and wherein the surface area of these sectors is used for calculating one or more parameters that express the print quality of the features, said parameters being suitable for determining a process window. The surface area of the sectors is determined on a contour of the printed pattern, obtainable from an CD-SEM image of the printed pattern. According to preferred embodiments, the parameters are ratios of surface area-based values divided by reference values. The reference values may be determined on the basis of the design intent of a pattern or on the basis of a contour extracted from a simulated print of the pattern.