Metrology Apparatus Calibration Stability via Virtual Target Library
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Solution Overview
Problem
Current monitoring approaches for lithographic processes face challenges in maintaining measurement stability, with indirect monitoring being unreliable due to unknown system parameters and direct monitoring interrupting tool operations and potentially providing false indications of instability.
Innovation Solution
A method involving defining monitoring target profiles, collecting and storing initial calibration data, compiling a library of spectra, and periodically updating calibration data to model metrology measurements, allowing for the determination of differences in modeling parameters and assessing tool stability without interrupting operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct monitoring of output measurements is performed by making measurements of actual physical targets, then measurement stability can be monitored directly, but tool operations are interrupted and false indications of instability may occur due to target property changes
Solution Approach 1:
The patent creates virtual copies of physical monitoring targets in the form of simulated targets with known properties. These virtual targets are used to generate reference measurements that can be compared against actual measurements without requiring physical target measurements, thereby avoiding tool interruptions while maintaining monitoring capability
Solution Approach 2:
The patent performs preliminary actions by pre-calculating and storing reference measurements for virtual targets under various conditions. This allows the system to have reference data ready for comparison before actual monitoring is needed, eliminating the need to interrupt operations for reference measurements
2Productivity
If indirect monitoring of system parameters is performed, then tool operations continue without interruption, but the monitoring reliability is reduced due to unknown relationships between monitored parameters and output measurements
Solution Approach 1:
The patent introduces virtual targets as an intermediary between direct physical target measurement and indirect system parameter monitoring. This intermediary provides a known reference framework that links system parameters to output measurements through simulated relationships, thereby improving monitoring reliability without requiring direct physical measurements
Solution Approach 2:
The patent utilizes parameter changes in virtual targets to simulate various measurement conditions and generate comprehensive reference data. By varying parameters such as target geometry, material properties, and measurement conditions in the virtual model, the system builds a robust reference framework that improves monitoring reliability
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 enhances measurement stability by continuously monitoring tool performance without user intervention, reducing logistical issues and avoiding false indications of instability, while maintaining tool availability and accuracy.
Implementation Method 1
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
properties of the scattered or reflected beam are measured
Data Source
AI summary
A method defines one or more monitoring target profiles, collects and stores initial calibration data of the metrology apparatus, compiling a library of spectra that would be observed from inspection of the monitoring target profiles using the metrology apparatus calibrated according to the initial calibration data. Some operations can be performed periodically, e.g., on a daily basis: obtaining current calibration data from the apparatus, modeling the effect of the current calibration data on the metrology apparatus operation, and using the result of the modeling and the contents of the library to determine any differences between one or more values of the initial calibration data and the current calibration data, and how these changes will be translated into changes in the measurement output for a given number of stacks and geometries.