Point Spread Function Extraction Using Isofocal Dose Measurements
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Solution Overview
Problem
Existing methods for determining the point spread function in electron beam lithography struggle with accurately decoupling electron-resist interactions from processing effects, leading to inaccuracies in proximity effect correction.
Innovation Solution
A method involving the exposure and development of a test substrate with a test pattern comprising sub-patterns of varying control widths, followed by isofocal dose measurements, to determine the imaging transfer function, specifically the point spread function, by modulating imaging parameters and calculating function parameters from the isofocal dose variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing methods are used to determine the point spread function, then the determination process can be completed, but the accuracy is insufficient due to inability to decouple electron-resist interactions from processing effects
Solution Approach 1:
The method segments the determination process into distinct phases: first determining the point spread function through electron-resist interaction analysis, then separately accounting for processing effects. This segmentation allows accurate decoupling of the two factors that were previously mixed in conventional single-step fitting methods.
Solution Approach 2:
The invention extracts the electron-resist interaction component (point spread function) as a separate determinable quantity from the combined measurement data. By using isofocal dose measurements and specific pattern geometries, the method isolates and determines the PSF parameters independently before applying processing effect corrections.
2Measurement precision
If conventional fitting methods are used, then the point spread function can be determined, but computational complexity is high and time-consuming
Solution Approach 1:
The method performs preliminary determination of the point spread function using isofocal dose measurements and specific pattern geometries before finalizing the complete exposure model. This preliminary action reduces the computational burden of subsequent processing effect corrections by having the PSF parameters already determined.
Solution Approach 2:
The invention changes the measurement approach by using isofocal dose measurements with specific pattern geometries (isolines, lines and spaces, gratings) instead of conventional critical dimension measurements. This parameter change simplifies the fitting process and reduces computational complexity while maintaining accuracy.
3Productivity
If isofocal dose measurements are used, then the determination process is faster and computationally simpler, but requires specific pattern geometries and measurement conditions
Solution Approach 1:
The method uses universal pattern geometries (isolines, lines and spaces, gratings) that can serve multiple purposes: determining the point spread function, verifying isofocality, and characterizing electron-resist interactions. These patterns are applicable across different exposure conditions and apparatus configurations.
Solution Approach 2:
The invention changes from conventional critical dimension measurements to isofocal dose measurements, which fundamentally alters the measurement paradigm. This parameter change enables faster determination with reduced computational complexity, as isofocal dose is inherently insensitive to certain processing variations that affect CD measurements.
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 allows for a more accurate determination of the point spread function, decoupling electron-resist interactions from processing effects, and enables faster and reduced computational complexity in determining isofocal doses and other PSF parameters.
Implementation Method 1
the interaction of the electron beam and the resist and substrate employed for the writing process... additional dose from backscattered electrons
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A method for determining parameters of an imaging transfer function (point spread function) is presented. With regard to a model that describes the imaging transfer function including a number of model parameters, a test substrate is exposed and developed using a test pattern (50) which comprises multiple sub-patterns (55) that are based on the same sub-pattern template but with varying control width of a feature in the template, such as the width of a line or a distance between lines. On the test substrate, isofocal dose measurements are performed using the structures thus formed on a test substrate with varying control and imaging parameters. The isofocal dose thus determined are utilized to determine the model parameters of the imaging transfer function.