Microscope Polarization Module for Lithographic Mask Measurement
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Solution Overview
Problem
Current microscopes for space-resolved measurements do not account for the polarization condition of electromagnetic radiation, leading to measurement errors due to polarization-dependent properties of optics and structures, which affects image contrast and edge position accuracy.
Innovation Solution
A microscope with an optical system having two eigen polarization conditions, where a polarization module sets the radiation polarization to known quantities matching these conditions, minimizing polarization-dependent errors and allowing precise measurement by accounting for intrinsic polarization properties of the system and structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional microscopy methods are used without accounting for polarization conditions, then the measurement process is simple, but measurement precision deteriorates due to polarization-dependent errors in image contrast and edge position
Solution Approach 1:
The patent applies parameter changes by systematically varying the polarization condition of the incident light (e.g., changing from linear to circular polarization) to compensate for polarization-dependent errors. By controlling and changing the polarization parameter of the illumination light, the system achieves higher measurement precision while maintaining manageable device complexity through computational correction methods.
2Measurement precision
If polarization conditions are not controlled, then the optical system is simple, but image contrast and edge position accuracy deteriorate due to polarization-dependent optical properties
Solution Approach 1:
The patent implements feedback by measuring the polarization state of light after it passes through the optical system and using this information to computationally correct the image data. The system feeds back the polarization information to adjust the measurement results, thereby improving edge position accuracy without requiring complex polarization-controlled optical components throughout the entire system.
3Reliability
If polarization-dependent properties of optics are ignored, then the measurement process is straightforward, but measurement errors increase due to intrinsic birefringence and stress-induced birefringence
Solution Approach 1:
The patent introduces an intermediary computational correction step that mediates between the raw image data and the final measurement results. This intermediary process accounts for polarization-dependent properties such as intrinsic birefringence and stress-induced birefringence by applying correction algorithms that translate the polarization effects into measurable errors, thereby improving reliability without requiring complex physical compensation mechanisms.
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 high-precision space-resolved measurement by maintaining consistent polarization conditions, reducing measurement errors and maximizing image contrast, particularly suitable for structures like lithographic masks and semiconductor wafers.
Implementation Method 1
the polarization condition of the electromagnetic radiation for illumination of the predetermined structure has not been taken into account in such microscopes so far. Also, changes in polarization properties, which change results from the optics of the microscope, e.g. from polarization-dependent properties of the lens coatings, intrinsic birefringence, stress-induced birefringence of glasses, as well as, in particular, of mirrors and beam splitters
Implementation Method 2
the predetermined structure is imaged onto a detector, with the contrast in the optical image on the detector strongly depending on the polarization condition of the irradiated light
Implementation Method 3
effects of electromagnetic interaction can cause a variation in the position of an edge of the structure in the optical image, depending on the polarization condition of the electromagnetic radiation used to illuminate the structure
Data Source
AI summary
A microscope is provided for space-resolved measurement of a predetermined structure. The microscope includes a source of radiation, which emits electromagnetic radiation of a predetermined wavelength, an optical system, which irradiates the electromagnetic radiation onto the structure to be measured and images the structure, irradiated with the electromagnetic radiation, onto a detector. The optical system has two eigen polarization conditions, and the optical system includes a polarization module by which a polarization condition can be set for the electromagnetic radiation of the source of radiation, the polarization conditions corresponding to the eigen polarization conditions.