Point Spread Function Calibration Using Isofocal Dose Measurements
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Solution Overview
Problem
Current methods for determining the point spread function in charged-particle exposure apparatuses are inaccurate due to incorporation of processing effects and require determining the full range of parameters, making it difficult to isolate backscattering parameters and resulting in high computational complexity and slow determination speed.
Innovation Solution
A method that involves exposing a test substrate with a test pattern having varying control parameters, performing isofocal dose measurements, and calculating the imaging transfer function by determining the isofocal dose and other parameters, allowing for decoupling of electron-resist interactions and processing effects, and using a mathematical model to fit the measurable quantities and imaging parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods are used to determine the point spread function, then the full range of parameters is determined, but the backscattering parameters cannot be isolated and the computational complexity increases
Solution Approach 1:
The patent extracts and isolates the backscattering parameters from the full set of point spread function parameters by using isofocal dose measurements. This is achieved by measuring the dose required to maintain constant focus across different aperture sizes, which specifically characterizes the backscattering component without requiring determination of all PSF parameters, thereby reducing computational complexity while maintaining accuracy
Solution Approach 2:
The patent segments the parameter determination process into distinct components: isofocal dose measurements for backscattering parameters and separate measurements for other parameters. This segmentation allows independent determination of backscattering characteristics, reducing the coupled complexity of determining the full parameter set simultaneously
2Measurement precision
If conventional methods are used to determine the point spread function, then all parameters are measured, but the determination speed is slow
Solution Approach 1:
The patent extracts the backscattering parameters through isofocal dose measurements, which can be performed independently and more quickly than full PSF characterization. This extraction approach separates the backscattering measurement from the complete PSF determination process, enabling faster acquisition of critical backscattering data without requiring time-consuming measurements of all other parameters
Solution Approach 2:
The patent performs partial action by measuring only the isofocal dose for backscattering parameter determination rather than conducting the complete set of measurements required for full PSF characterization. This partial measurement approach achieves the specific goal of obtaining backscattering parameters with reduced measurement time and faster determination speed
3Reliability
If processing effects are included in the measurement, then the full exposure process is captured, but the electron-resist interactions cannot be isolated
Solution Approach 1:
The patent extracts the electron-resist interaction characteristics by using isofocal dose measurements that specifically probe the resist response to backscattered electrons. By measuring the dose required to maintain constant focus in the resist, the method isolates the electron-resist interaction from other processing effects such as development and etching, enabling precise characterization of the primary exposure physics
Solution Approach 2:
The patent segments the exposure process characterization into distinct components: isofocal dose measurements for electron-resist interactions and separate process measurements for development and etching. This segmentation allows independent and precise measurement of electron-resist interactions without the confounding influence of subsequent processing effects
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 faster and more accurate determination of the point spread function, particularly isolating backscattering parameters, with reduced computational complexity and improved precision in proximity effect correction in electron beam lithography.
Implementation Method 1
describing the distribution of dose or energy generated at the target plane resulting from a single active element... in response to a particle beam generated by means of a single active element
Data Source
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 which comprises multiple sub-patterns 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.