Defect Detection Device Using Microlens Array and Digital Mask Processing
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Solution Overview
Problem
Current defect detection systems for unpatterned semiconductor wafers face challenges in high sensitivity and throughput for multiple defect types, particularly due to misalignment issues between appearance inspection devices and scanning electron microscopes, and the complexity of incorporating spatial filters in optical systems.
Innovation Solution
A defect detection device and method utilizing a microlens array and imaging element to form and process scattered light images, with a mask image storage unit and calculation unit for mask processing, allowing for high-speed detection of multiple defect types without the need for a spatial filter between objective and imaging lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spatial filter is incorporated in the optical path between objective lens and imaging lens to detect multiple types of defects with high sensitivity, then defect detection sensitivity is improved, but device complexity increases and optical system size increases
Solution Approach 1:
The patent extracts the spatial filtering function from the physical optical path and implements it through digital image processing. Instead of placing physical spatial filters in the optical path between the objective lens and imaging lens, the system captures images and applies digital filtering algorithms to achieve the same defect detection sensitivity for multiple defect types without adding physical filter components.
Solution Approach 2:
The patent replaces the mechanical/optical spatial filter system with a digital image processing system. The spatial filtering operation that would traditionally require physical filters and complex optical paths is substituted with digital algorithms applied to captured images, thereby simplifying the optical system while maintaining defect detection sensitivity.
2Adaptability or versatility
If multiple spatial filters are switched to detect different types of defects, then defect detection versatility is improved, but detection time increases due to multiple image captures
Solution Approach 1:
The patent enables continuous defect detection for multiple defect types by capturing a single image and applying multiple digital filtering algorithms sequentially in software. This eliminates the need to switch between multiple physical filters and capture multiple images, maintaining continuous detection capability while reducing detection time.
Solution Approach 2:
The patent creates digital copies of spatial filter characteristics through algorithms rather than using multiple physical filter copies. Each defect type detection is achieved by applying a corresponding digital filter algorithm to the same captured image, eliminating the need for multiple physical filter switching operations.
3Speed
If a digital mirror device is used as a spatial filter to enable quick switching for multiple defect types, then defect detection speed is improved, but device complexity and optical system size increase
Solution Approach 1:
The patent replaces the digital mirror device (DMD) or liquid crystal filter with pure software-based digital image processing algorithms. This substitution eliminates the need for complex electro-optical switching devices while achieving the same functionality of detecting multiple defect types through digital filtering applied to captured images.
Solution Approach 2:
The patent extracts the filtering functionality from the optical domain and relocates it to the digital signal processing domain. By taking out the need for physical or electro-optical filter switching devices, the system achieves defect type versatility through software algorithms without adding complex hardware components.
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 high sensitivity and speed in detecting multiple defect types, improving the success rate of automatic imaging and throughput in SEM observation, while allowing for a compact optical system design.
Implementation Method 1
a scanning electron microscope (SEM) is used in an observation device
Implementation Method 2
an optical system configured to form scattered light produced by a light irradiation into an image
Implementation Method 3
a microlens array disposed at an image plane of the optical system; an imaging element disposed at a position offset from the imaging plane of the optical system and configured to image light that passes through the microlens array
Data Source
AI summary
The invention is to provide a defect detection device capable of using a compact optical system to detect a plurality of types of defects with high sensitivity and high speed. The defect detection device includes an irradiation system that irradiates light onto an object to be inspected; an optical system that forms scattered light produced by a light irradiation into an image; a microlens array disposed at an image plane of the optical system; an imaging element that is disposed at a position offset from the imaging plane of the optical system and that images light that passes through the microlens array; a mask image storage unit that stores a plurality of mask images generated for each type of defect or each defect direction; and a calculation unit that carries out mask processing on an image obtained from the imaging element using the plurality of mask images and carries out defect detection processing.