Focus Metrology Mark for Lithography Defocus Monitoring
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Solution Overview
Problem
As semiconductor device integration densities increase, existing lithography techniques face challenges in precisely monitoring critical dimension (CD) uniformity and focal variations during the manufacturing process, which can lead to defects in integrated circuit (IC) devices.
Innovation Solution
A photomask and substrate target with a focus metrology mark, comprising reference and shift photoresist patterns, are used to analyze light beam characteristics and measure focal variations through diffraction-based methods, allowing for precise and non-destructive in-line monitoring of focal variations during the lithographic process without adding additional manufacturing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If integration density of semiconductor devices is increased, then device functionality and performance are improved, but measurement precision of critical dimension and focal variation deteriorates
Solution Approach 1:
The substrate is divided into multiple regions including a first region with feature patterns and a second region with focus metrology marks. This segmentation allows separate measurement areas that do not interfere with each other, enabling precise focal variation measurement through the focus metrology mark while maintaining high integration density in the feature pattern region.
Solution Approach 2:
The focus metrology mark serves as an intermediary structure between the exposure process and measurement process. It includes reference and shift photoresist patterns that are exposed simultaneously with feature patterns but can be measured separately using diffraction-based methods, thus enabling indirect measurement of focal variations without directly measuring the critical dimensions of feature patterns.
2Measurement precision
If separate measurement process is added to monitor lithographic process, then measurement precision is improved, but manufacturing complexity and time increase
Solution Approach 1:
The focus metrology mark is merged with the feature patterns on the same substrate and exposed simultaneously in the same lithographic process. The reference and shift photoresist patterns are formed together with feature patterns using the same exposure conditions, combining the measurement target creation with the manufacturing process rather than adding a separate measurement process.
Solution Approach 2:
The focus metrology mark structure serves multiple functions: it acts as both a measurement target for focal variation monitoring and as part of the overall lithographic pattern set. The same exposure process that creates feature patterns also creates the focus metrology mark, making the measurement structure universal to the manufacturing process.
3Ease of operation
If conventional lithography monitoring is used, then process simplicity is maintained, but measurement precision of minute focal variations deteriorates
Solution Approach 1:
The patent replaces direct mechanical or physical measurement methods with diffraction-based optical measurement. Light beams are diffracted by the focus metrology mark and the characteristics of diffracted light are analyzed to determine focal variations, substituting direct measurement with indirect optical detection that achieves higher precision for minute variations.
Solution Approach 2:
The measurement approach changes from directly measuring critical dimensions to measuring diffraction parameters of light beams. By analyzing the characteristics of diffracted light (such as diffraction efficiency, intensity distribution) instead of directly measuring physical dimensions, the system achieves higher sensitivity to focal variations while maintaining process simplicity.
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 enables improved CD uniformity and reliable IC device manufacturing by accurately determining focal variations and overlay errors, thereby enhancing the precision and reliability of the lithographic process.
Implementation Method 1
characteristics of diffracted light beams, as diffracted by a focus metrology mark
Data Source
AI summary
A photomask includes a focus metrology mark region that includes a plurality of focus monitor patterns. To measure a focal variation of a feature pattern formed on a substrate, a substrate target for lithography metrology including a focus metrology mark formed on the same level as the feature pattern is used. A lithography metrology apparatus includes a projection device including a polarizer; a detection device detecting the powers of ±n-order diffracted light beams from among output beams diffracted by the focus metrology mark of a to-be-measured substrate; and a determination device which determines, from a power deviation between the ±n-order diffracted light beams, defocus experienced by the feature pattern.