Pattern Inspection Optics With Integrated Autofocus for Mask Defects
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Solution Overview
Problem
Existing pattern inspection apparatuses face challenges in accurately adjusting focus due to shallow focal depth and dependency on illumination conditions and patterns, leading to insufficient accuracy in detecting ultrafine defects on semiconductor masks.
Innovation Solution
A pattern inspection apparatus with a movable stage, imaging sensor, and autofocus mechanism that uses multiple detection elements to capture images at different focus positions, allowing for independent focus adjustment without relying on illumination conditions or patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an independent autofocus mechanism is used near the inspection optical system, then the autofocus operation is simplified, but the measurement accuracy is insufficient because it cannot detect temperature and mechanical deformation fluctuations of the inspection optical system
Solution Approach 1:
The patent combines the autofocus function with the inspection optical system itself, merging the measurement function into the inspection system. The inspection optical system performs both defect inspection and focal position detection, eliminating the need for a separate autofocus mechanism and ensuring that temperature and mechanical deformation fluctuations are detected accurately.
Solution Approach 2:
The inspection optical system is given multiple functions: it serves both as the defect inspection system and as the autofocus measurement system. By using the same optical system for both purposes, the patent ensures that the measurement of focal position accurately reflects the actual inspection conditions, including temperature and mechanical deformation effects.
2Measurement precision
If the focal depth of the inspection optical system is reduced to detect ultrafine defects, then the measurement precision is improved, but the focal depth becomes shallower making focus maintenance more difficult
Solution Approach 1:
The patent implements a feedback mechanism where the inspection optical system continuously measures the focal position by detecting the reflected light from the mask surface. The measured focal position information is fed back to adjust the stage height or objective lens position, maintaining the inspection plane within the shallow focal depth and enabling stable focus during inspection.
Solution Approach 2:
The inspection optical system performs self-measurement of its own focal position by utilizing the reflected light from the inspection object itself. This self-service capability allows the system to autonomously detect and correct focus deviations without requiring external autofocus mechanisms, maintaining stable focus despite the shallow focal depth.
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
Enables precise focus adjustment, improving the accuracy of defect detection on semiconductor masks by capturing and comparing images at varying focus positions, thereby enhancing the inspection process.
Implementation Method 1
a plurality of first detection elements that detect light flux transmitted through or reflected by the target object illuminated with inspection light and capture a pattern image of the target object
Implementation Method 2
a plurality of second detection elements that are arranged adjacent to the plurality of first detection elements, detect light fluxes obtained by shifting a focus position of the light flux front side and rear side, and capture images for focus adjustment
Data Source
AI summary
According to one aspect of the present invention, a pattern inspection apparatus includes: an imaging sensor including a plurality of first detection elements that detect light flux transmitted through or reflected by a target object illuminated with inspection Light and capture a pattern image of the target object, and a plurality of second detection elements that are arranged adjacent to the plurality of first detection elements, detect Light fluxes obtained by shifting a focus position of the light flux front side and rear side, and capture images for focus adjustment; an adjustment mechanism configured to adjust a focal position of the light flux by using the images for the focus adjustment captured by the plurality of second detection elements; and a comparison circuit configured to compare the pattern image captured by the plurality of first detection elements and a predetermined reference image.