Model-Based Photomask Registration and Critical Dimension Metrology
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Solution Overview
Problem
Traditional target-based registration methods in metrology face limitations such as registration differences between functional device patterns and targets, limited mask coverage, inability to measure high spatial frequency components, and interference with device function, leading to inaccurate measurements and restricted mask types and pattern sizes.
Innovation Solution
A model-based registration and critical dimension metrology method that uses imaging devices to obtain optical images, generates simulated images based on mask designs, and adjusts parameters to minimize dissimilarity, allowing for accurate measurement of functional device patterns without pre-defined metrology targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional target-based registration methods are used, then registration measurement can be performed, but measurement accuracy deteriorates due to registration differences between functional device patterns and targets
Solution Approach 1:
The invention extracts and removes the metrology targets from the measurement process entirely. Instead of using separate targets, the method directly measures functional device patterns on the mask, eliminating the registration difference problem between targets and functional patterns.
Solution Approach 2:
The functional device patterns serve dual purposes: they are both the actual device patterns to be manufactured and the measurement targets for registration verification. This eliminates the need for separate metrology targets and ensures measurement relevance to actual device performance.
2Measurement precision
If traditional target-based registration methods are used, then registration can be measured, but mask coverage is limited
Solution Approach 1:
Functional device patterns across the entire mask serve as measurement targets, enabling registration verification at all locations where devices are manufactured, not just at discrete target locations. This dramatically increases mask coverage.
Solution Approach 2:
The functional device patterns themselves provide the measurement information needed for registration verification, eliminating the need for separate dedicated measurement targets and enabling full-mask utilization for both manufacturing and measurement.
3Measurement precision
If traditional target-based registration methods are used, then simple patterns can be measured, but high spatial frequency components cannot be measured
Solution Approach 1:
The invention changes the measurement approach from direct geometric target measurement to model-based simulation comparison. By using aerial image simulation and comparing simulated versus actual aerial images, the system can extract high spatial frequency registration information that is not directly observable in simple optical images.
Solution Approach 2:
An aerial image simulation model serves as an intermediary between the mask pattern and the measurement system. The model translates mask patterns into expected aerial images, allowing indirect measurement of high spatial frequency components through comparison with actual aerial images from the lithography process.
4Measurement precision
If metrology targets are inserted in mask layout, then registration measurement is enabled, but device function is interfered with
Solution Approach 1:
The invention extracts and eliminates the separate metrology targets from the mask layout. Registration measurement is performed directly on functional device patterns, removing the harmful element (targets) that interfered with device function while preserving measurement capability.
Solution Approach 2:
Functional device patterns serve the dual function of being both the actual device structures to be manufactured and the measurement targets for registration verification. This eliminates the need for separate metrology targets that caused interference.
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 accurate registration and critical dimension measurements directly from functional device patterns, improving measurement accuracy, increasing mask coverage, and effectively measuring high spatial frequency components, thus enhancing the understanding and control of mask contributions to overlay budgets.
Implementation Method 1
utilizing an imaging device to obtain at least one optical image of a measurement site specified for a photomask
Data Source
AI summary
A method and system for performing model-based registration and critical dimension measurement is disclosed. The method includes: utilizing an imaging device to obtain at least one optical image of a measurement site specified for a photomask; retrieving a design of photomask and utilizing a computer model of the imaging device to generate at least one simulated image of the measurement site; adjusting at least one parameter of the computer model to minimize dissimilarities between the simulated images and the optical images, wherein the parameters includes at least a pattern registration parameter or a critical dimension parameter; and reporting the pattern registration parameter or the critical dimension parameter of the computer model when dissimilarities between the simulated images and the optical images are minimized.