Projection Objective Distortion Measurement via Positional Deviation
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Solution Overview
Problem
Current methods for measuring distortion of a projection objective in lithography machines are either limited by high dependency on reticle alignment systems, costly and complex image quality sensors, or lack adaptability across different lithography machines, making them unsuitable for precise and high-order distortion measurement.
Innovation Solution
A method involving a stepping and exposing process where positional deviations between patterns formed on a substrate are calculated to derive distortion of the projection objective, using common overlay marks and integrating the measurement into the normal operation of the lithography machine, reducing the need for external devices and enhancing adaptability across various machine types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If reticle alignment sensors are used to measure distortion, then measurement can be performed using existing lithography machine components, but measurement precision is limited and high-order distortions cannot be accurately measured
Solution Approach 1:
The patent introduces a specialized alignment mark grating as an intermediary measurement target with precisely controlled periodic structures. This grating serves as a mediator between the projection objective and measurement system, enabling high-precision distortion measurement through its known geometric features that amplify and reveal optical path deviations
Solution Approach 2:
The patent transforms the measurement approach by changing from direct distortion measurement to measuring positional deviations of alignment marks. By converting distortion effects into measurable position shifts of the grating patterns, the system achieves high-precision measurement capability while maintaining compatibility with existing lithography machine alignment sensors
2Measurement precision
If image quality sensors are used to measure distortion, then high-order distortions can be measured with high precision, but the sensors are costly and have complex structure reducing adaptability
Solution Approach 1:
The patent creates a simplified copy or model of the alignment mark grating pattern on the substrate. By measuring the positional deviation of this copied pattern from its expected position, the system derives distortion information without requiring complex image quality sensors. The measurement is achieved through comparing the actual marked positions with the known original grating geometry
Solution Approach 2:
The patent replaces expensive, delicate image quality sensors with a disposable or consumable alignment mark grating. The grating is a simple optical element that can be manufactured at low cost and does not require complex maintenance or calibration, making the measurement system adaptable to various lithography machines regardless of their budget constraints
3Ease of manufacture
If reticle alignment approach is used, then measurement can be performed with existing components, but the method is limited by specific alignment approaches and cannot work with CCD alignment approaches
Solution Approach 1:
The patent designs the alignment mark grating and measurement method to be universal across different alignment approaches. The periodic grating pattern and its deviation measurement principle work equally well with optical alignment sensors, CCD cameras, or other detection methods, making the measurement system adaptable to various lithography machine configurations without requiring approach-specific modifications
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 achieves high precision and adaptability in measuring projection objective distortion, reducing manufacturing costs and improving measurement accuracy, making it suitable for both high-end and low-end lithography machines without limitations on alignment approaches.
Implementation Method 1
a projection objective, configured to project the plurality of marks onto the substrate
Implementation Method 2
expose and transfer a reticle pattern onto a photoresist
Data Source
Figure 1~2
Figure 3~4C
Figure 5
AI summary
A method for measuring distortion of a projection objective, which includes: obtaining a plurality of first positional deviations between two groups of patterns formed respectively after two exposures performed in a same exposure field during a stepping and exposing process of the reticle stage (S21); obtaining a plurality of second positional deviations between two groups of patterns formed respectively after another two exposures performed in a same exposure field during a stepping and exposing process of the workpiece stage (S22); subtracting motional errors of the reticle stage and/or workpiece stage from each of the plurality of first and second positional deviations to obtain corresponding first and second corrected deviations (S43, S44); calculating differences each between a pair of corrected deviations (S45); and calculating the distortion of the projection objective by a fitting process (S46).