Photolithographic Mask Pixel Stress Birefringence Calibration
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Solution Overview
Problem
Current methods for correcting defects in photolithographic masks, such as registration errors and optical transmission variations, rely on indirect calibration processes that are not suitable for future EUV masks, as they use actinic wavelength calibration which is not applicable to reflective optical elements and do not accurately measure the primary effect of error-correcting pixels, leading to potential introduction of new errors.
Innovation Solution
The method determines the effect of pixels introduced into the mask substrate by measuring the change in birefringence caused by stress, allowing for direct calibration of the defect correction process independent of the actinic wavelength, using stress birefringence as the primary quantity for determining the effect of error-correcting pixels, and linking this with optical transmission variation to ensure precise control of the laser beam parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If actinic wavelength calibration is used to determine the effect of error-correcting pixels, then calibration can be performed for conventional masks, but the method is not applicable to EUV masks and may introduce new errors due to indirect measurement
Solution Approach 1:
The patent replaces the indirect optical transmission measurement method with a direct stress measurement method using birefringence. Instead of measuring optical effects at actinic wavelengths, the invention uses stress-optic coefficients to directly measure the physical stress induced by pixels, substituting an indirect optical measurement system with a direct mechanical stress measurement system that is applicable to all mask types including EUV masks.
Solution Approach 2:
The patent introduces stress birefringence as an intermediary measurement parameter that links the physical effect of pixel-induced stress to the final optical transmission impact. By measuring stress through birefringence changes and using stress-optic coefficients as a mediator, the method enables accurate prediction of optical effects without direct actinic wavelength measurement, making the process applicable to both conventional and EUV masks.
2Ease of manufacture
If indirect calibration processes are used to correct mask defects, then the correction process can be simplified, but new errors may be introduced due to inaccurate measurement of pixel effects
Solution Approach 1:
The patent implements a feedback mechanism where stress birefringence measurements are taken before and after pixel writing, and the change in birefringence is used to calculate the actual stress induced. This feedback information is then used to adjust subsequent pixel writing parameters, ensuring accurate control of optical transmission effects and preventing the introduction of new errors while maintaining correction simplicity.
3Productivity
If laser beam parameters are not precisely controlled during pixel writing, then the correction process is faster and simpler, but optical transmission variation exceeds tolerable limits and introduces new errors
Solution Approach 1:
The patent performs preliminary stress birefringence measurements on the mask substrate before writing correction pixels. This preliminary characterization of the substrate's stress-optic properties enables precise prediction of how each pixel will affect optical transmission, allowing for pre-calculation of optimal pixel parameters that will achieve the desired correction without exceeding transmission tolerances, thus maintaining both speed and precision.
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 effectively corrects defects in photolithographic masks without introducing new errors, enabling precise control of pixel writing to maintain optical transmission within tolerable limits, and is applicable to both conventional and EUV masks by decoupling the calibration from the actinic wavelength, ensuring accurate and reliable defect correction.
Implementation Method 1
A laser beam has been used for inducing stress into a mask substrate or simply for ablation of a mask substrate
Implementation Method 2
determining the effect of the one or more introduced pixels by determining a change in birefringence of the substrate of the photolithographic mask
Data Source
AI summary
The present invention refers to a method for determining an effect of one or more of pixels to be introduced into a substrate of a photolithographic mask, the photolithographic mask having one or more pattern elements, wherein the one or more pixels serve to at least partly correct one or more errors of the photolithographic mask, the method comprising: determining the effect of the one or more introduced pixels by determining a change in birefringence of the substrate of the photolithographic mask having the one or more pattern elements.