Optical Path Length Scanning for Low-Noise Wafer Inspection
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Solution Overview
Problem
The challenge of capturing images of semiconductor wafers and photomasks is exacerbated by fine irregularities causing noise due to deviations from the focal position, leading to reduced inspection accuracy.
Innovation Solution
An optical apparatus with an optical path length adjustment mechanism that changes the distance between the object and detector, acquiring multiple images at varying focal positions to integrate and cancel noise from irregularities, using a detector, optical system, and processors to generate a cumulative image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an image of the sample is captured at a fixed focal position, then the inspection process is simple and fast, but noise caused by minute irregularities deteriorates inspection accuracy
Solution Approach 1:
The optical path length adjustment mechanism periodically changes the optical path length between the object and detector to capture multiple images at different focal positions. This periodic variation in focal position allows the system to distinguish between noise from irregularities and actual defects, thereby improving inspection accuracy without requiring complex post-processing
Solution Approach 2:
The system changes the optical path length parameter to capture multiple images at different focal positions. By varying this physical parameter, the system can separate noise signals from actual defects, improving measurement precision while maintaining a relatively simple inspection process
2Measurement precision
If the optical path length is adjusted to capture multiple images, then noise from irregularities is reduced, but the inspection time increases
Solution Approach 1:
The optical path length adjustment mechanism continuously captures multiple images at different focal positions during a single inspection process. This continuous action allows the system to accumulate sufficient data to reduce noise while minimizing the total inspection time compared to repeated separate measurements
Solution Approach 2:
By using periodic changes in optical path length to capture multiple images efficiently, the system reduces noise through cumulative data while maintaining inspection speed. The periodic nature allows for optimized capture rates that balance noise reduction with time efficiency
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 reduces noise in captured images, enhancing the accuracy of defect inspection by integrating images in different focal states, thereby improving inspection quality.
Implementation Method 1
an optical system configured to irradiate an object with illumination light and guide a secondary ray generated when the object is irradiated with the illumination light to the detector
Implementation Method 2
an optical system configured to irradiate an object with illumination light and guide a secondary ray generated when the object is irradiated with the illumination light to the detector
Implementation Method 3
a detector configured to detect light
Data Source
AI summary
An optical system irradiates an object with illumination light and guides a secondary ray generated when the object is irradiated with the illumination light to a detector. Optical path length adjustment mechanism adjusts an optical path length between the object and the detector. one or more processors execute a program stored in a memory to: generate an image of the object based on detection results of the secondary ray by the detector, control the optical path length adjustment mechanism to change the optical path length between the object and the detector, acquire multiple images of the object while changing the optical path length between the object and the detector, and generate the image of the object based on a cumulative result of the acquired multiple images.