EUV Mask Inspection Synchronization for Luminance Correction
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Solution Overview
Problem
Existing inspection methods for EUV masks using pulsed light sources suffer from luminance unevenness errors due to variations in light emission, which are not adequately corrected by existing technologies, leading to inaccuracies in defect detection.
Innovation Solution
A detection method and apparatus that utilize a synchronization control between inspection and correction detectors, along with a cut mirror to adjust the luminance distribution, ensuring accurate correction of luminance unevenness by controlling light emission timing and pixel alignment, thereby minimizing errors caused by differences in pulse numbers between detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a pulsed light source is used for illumination, then the luminance of illumination light is improved, but luminance unevenness occurs due to variations in light emission from one pulse to another
Solution Approach 1:
The patent employs a correction detector to monitor the luminance distribution of each pulse in real-time and feeds this information back to correct the inspection image data. The processing unit uses the detected luminance distribution to calculate correction values and apply them to remove artifacts caused by luminance unevenness, thereby maintaining reliable defect detection despite pulsed light variations.
Solution Approach 2:
The correction detector acts as an intermediary between the pulsed light source and the inspection system. It separately detects the luminance distribution of the illumination light without being affected by the inspection object, providing correction data that mediates the impact of luminance unevenness on the final inspection results.
2Measurement precision
If a correction detector is added to detect luminance distribution, then luminance unevenness correction capability is improved, but device complexity increases
Solution Approach 1:
The correction detector uses the same TDI sensor structure and pulsed light illumination as the inspection detector, allowing a single light source to serve dual purposes. The system processes both inspection image data and luminance distribution data through a unified detection platform, reducing overall system complexity while maintaining high measurement precision.
Solution Approach 2:
The correction detector creates a copy of the luminance distribution information separately from the inspection imaging path. This copied data represents the illumination characteristics without containing object information, enabling independent correction processing that simplifies the overall system architecture by separating measurement functions.
3Adaptability or versatility
If the number of pixels in transfer direction differs between inspection detector and correction detector, then detection flexibility is improved, but errors occur due to difference in number of pulses emitted within cumulative time period
Solution Approach 1:
The patent introduces dynamic adjustment of the transfer cycle for the correction detector based on the pulse emission frequency. By making the transfer cycle variable and synchronized with the light source pulse rate, the system maintains accurate pulse-counting correspondence even when pixel numbers differ, allowing flexible detector configurations without sacrificing measurement precision.
Solution Approach 2:
The system changes the transfer cycle parameter of the correction detector to match the pulse emission characteristics. By adjusting this temporal parameter rather than requiring identical spatial parameters (pixel numbers), the system achieves accurate pulse counting and luminance correction while maintaining detection flexibility for different detector configurations.
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 accurate detection and correction of luminance unevenness, ensuring precise inspection of EUV masks by maintaining synchronization and adjusting pixel alignment, thus preventing errors in defect determination.
Implementation Method 1
acquiring image data of a luminance distribution of the illumination light, the luminance distribution being detected by illuminating a correction detector by using part of the illumination light
Implementation Method 2
acquiring image data of the object to be inspected by concentrating light from the object to be inspected illuminated by the illumination light and detecting the concentrated light by an inspection detector
Data Source
AI summary
A detection method, an inspection method, a detection apparatus, and an inspection apparatus capable of preventing an error in a luminance unevenness correction and thereby accurately inspecting an object to be inspected are provided. A detection method according to the present disclosure includes illuminating an object to be inspected by using illumination light including pulsed light, acquiring image data of the object to be inspected by concentrating light from the object to be inspected illuminated by the illumination light and detecting the concentrated light by an inspection detector, acquiring image data of a luminance distribution of the illumination light, the luminance distribution being detected by illuminating a correction detector by using part of the illumination light, and detecting inspection image data by correcting the image data of the object to be inspected based on the image data of the luminance distribution.