Mask Metrology Sensor Linearity Adaptation
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Solution Overview
Problem
Mask-metrology measurement apparatuses face accuracy and repeatability losses when replacing image sensors due to non-linearity differences between old and new sensors, affecting measurement results and user routines.
Innovation Solution
A method that involves recording an image with a first image sensor, generating an aerial image through clear normalization, applying linearity correction, and imprinting a linearity signature of a second image sensor to adapt the image data, ensuring measurement results match those from the old sensor by mathematically combining and normalizing the images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If an image sensor is replaced in the measurement apparatus, then the device can continue to operate with updated components, but the measurement precision deteriorates due to non-linearity differences between old and new sensors
Solution Approach 1:
The patent creates a digital copy of the old image sensor's linearity characteristics by recording reference images with the old sensor and applying its linearity correction values to images taken with the new sensor. This copying approach allows the new sensor to replicate the measurement behavior of the old sensor, maintaining measurement precision while enabling sensor replacement and extending the operational lifespan of the measurement apparatus.
2Measurement precision
If linearity correction is applied to raw images directly, then measurement results can be corrected, but accuracy is lost due to non-linearity differences between old and new sensors
Solution Approach 1:
The patent performs preliminary action by recording reference images and determining linearity correction values with the old image sensor before replacing it with the new sensor. These pre-determined correction values are then applied to images taken with the new sensor, ensuring that the measurement accuracy is preserved by using correction data from the original sensor that established the measurement baseline.
3Adaptability or versatility
If different image sensors are used before and after replacement, then the measurement apparatus can maintain operation, but repeatability deteriorates due to non-identical non-linearity behaviours
Solution Approach 1:
The patent changes the parameter approach by instead of trying to make different sensors identical, it transfers the linearity correction parameters (characteristics) from the old sensor to the new sensor through the application of reference image data. This parameter transfer enables different sensors to produce identical measurement results, maintaining repeatability while allowing sensor replacement and demonstrating adaptability.
Data Source
AI summary
Method for operating a mask-metrology measurement apparatus, wherein an image of a section of a photomask is recorded with a first image sensor and wherein an aerial image is generated by virtue of the image raw data obtained with the image sensor being subjected to a clear normalization. The aerial image is subjected to a non-linearity adaptation, which comprises the following steps. In step a., the aerial image is mathematically combined with a clear image (CT2T). In step b., linearity correction (Plin1) is applied to the image data generated in step a. to correct a linearity error of the first image sensor. In step c., a non-linearity adaptation (P−1lin2) is applied to the linearity-corrected image data obtained in step b. to imprint a linearity signature of a second image sensor not arranged in the beam path of the measurement apparatus on the image data. In step d., a clear normalization is applied to the linearity-adapted image data generated in step c. The invention also relates to a mask-metrology measurement apparatus and to a computer program product.