Variable Direction Differential Interference Optical System for Mask Defect Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional defect inspecting apparatuses for mask patterns face challenges in reliably detecting defects across all directions due to limitations in differential interference optical systems, particularly with phase shift masks where the boundary between trench and un-trenched regions has low contrast, making it difficult to detect defects sensitively in all directions.
Innovation Solution
A defect inspecting apparatus utilizing a differential interference optical system that varies the direction of light ray separation to produce differential interference images, allowing for comparison with reference images to detect defects across various orientations, ensuring reliable detection of defects in phase difference patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a differential interference optical system with a fixed separating direction is used, then the boundary detection sensitivity is significantly improved when the separating direction is perpendicular to the boundary line, but the detection capability is lost when the separating direction is parallel to the boundary line
Solution Approach 1:
The patent applies the dynamics principle by making the separating direction of the differential interference optical system variable rather than fixed. The control unit dynamically adjusts the separating direction based on the orientation of the boundary line, ensuring that the separating direction is always substantially perpendicular to the boundary line. This dynamic adaptation resolves the contradiction by maintaining high detection sensitivity for boundaries in any orientation without requiring multiple fixed-direction systems.
Solution Approach 2:
The patent employs parameter changes by varying the orientation parameter of the differential interference optical system. The control unit changes the separating direction parameter according to the boundary line orientation, transforming the system from a static fixed-direction configuration to a dynamic variable-direction configuration. This parameter adjustment enables the system to maintain optimal detection sensitivity across all boundary orientations.
2Measurement precision
If the separating direction is fixed perpendicular to a specific boundary line, then high detection sensitivity is achieved for that specific orientation, but defects in other directions cannot be reliably detected
Solution Approach 1:
The system dynamically adjusts the separating direction to match the boundary line orientation, ensuring reliable defect detection in all directions. The control unit receives boundary line orientation information and automatically adjusts the differential interference optical system's separating direction accordingly, making the system adaptable to any boundary orientation rather than being limited to a fixed direction.
Solution Approach 2:
The patent implements universality by enabling a single differential interference optical system to effectively detect boundaries in all orientations. By making the separating direction variable and controllable, the system achieves multi-functional capability to handle various boundary line orientations (0°, 45°, 90°, etc.) with a single device, rather than requiring multiple specialized systems for different orientations.
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
The apparatus effectively detects defects in mask patterns by varying the differential interference effect across different directions, enhancing sensitivity and reliability in detecting defects on phase shift masks, regardless of the boundary orientation, thereby improving the detection of defects in all directions.
Implementation Method 1
The differential interference optical system is implemented utilizing a birefringence prism that separates a bundle of light rays into smaller bundles separated from each other by a very small angle. Specifically, the birefringence prism separates a bundle of transmitted light rays or reflected light rays from a mask into a bundle of ordinary rays and a bundle extraordinary rays separated from each other by a very small angle.
Implementation Method 2
The two bundles of light rays resulting from the separation interfere with each other at an image formed surface. The intensities of the bundles of light rays vary depending on a phase difference.
Data Source
AI summary
In a defect inspecting apparatus, a differential interference optical system forms a differential interference image which is produced from an optical interference of images in a predetermined direction, the images corresponding to inspecting parts of a pattern formed on a mask. A control part varies the predetermined direction so as to cause the differential interference optical system to produce another differential interference image. An image pickup sensor picks up the differential interference images in accordance with the variation of the predetermined direction. A defect detecting unit detects a defect in the pattern formed on the mask from comparing the differential interference images with reference images, respectively.