Magnetic Disk Inspection Using Multi-Angle Light Detection
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Solution Overview
Problem
Conventional methods for inspecting magnetic disks fail to accurately distinguish between small concave and convex defects on glass substrates, leading to incorrect defect classification and potential double counting of defects, which can result in defective products being overlooked or misidentified.
Innovation Solution
A disk surface inspection apparatus and method that utilizes a stage unit, illumination units, regular reflection light detection, low angle scattered light detection, and high angle scattered light detection to process signals from multiple detectors, enabling the accurate differentiation and classification of concave and convex defects on the surface of magnetic disks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical inspection methods using single detector or simple reflected light detection are used, then the device complexity is low, but the measurement precision for distinguishing concave and convex defects is insufficient
Solution Approach 1:
The detection system is segmented into multiple specialized detectors: a first detector for regular reflection light, a second detector for scattered light in the vicinity of regular reflection, and a third detector for scattered light at higher angles. Each detector captures specific light characteristics to enable precise differentiation between concave and convex defects through pattern analysis.
Solution Approach 2:
The inspection system transitions from single-dimensional reflected light detection to multi-dimensional detection by capturing light intensity distribution across different angular dimensions. The multiple detectors are positioned to receive light at different angles, creating a dimensional expansion that enables accurate defect classification.
2Reliability
If simple reflected light intensity detection is used, then the ease of operation is high, but the reliability of defect identification is insufficient leading to erroneous determination
Solution Approach 1:
The system employs feedback mechanisms where detection signals from multiple detectors are processed to determine light intensity distribution patterns. The processing unit analyzes these patterns and provides feedback to classify defects as concave or convex, ensuring reliable identification through systematic pattern recognition rather than simple threshold detection.
Solution Approach 2:
The inspection method changes parameters by detecting light intensity distribution across multiple angular positions rather than relying on a single intensity value. By analyzing how light intensity varies across different detection angles, the system reliably distinguishes between concave and convex defects regardless of contamination or surface conditions.
3Measurement precision
If comprehensive multi-detector optical inspection system is implemented, then the measurement precision for defect classification is improved, but the productivity is reduced due to complex signal processing
Solution Approach 1:
The system performs preliminary action by capturing all necessary light detection data simultaneously through multiple detectors positioned at different angles. The processing unit receives and analyzes these signals in an integrated manner, enabling rapid classification of defects as concave or convex without requiring sequential measurements or complex iterative processing.
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 the precise detection of small concave and convex defects, allowing for their separation from other defects and foreign materials, thereby increasing production yield by removing defective substrates early in the production process.
Implementation Method 1
a first regular reflection light detection unit for detecting the regular reflection light reflected from the surface on the front side of the sample irradiated with the light by the first illumination unit
Implementation Method 2
a first low angle scattered light detection unit for detecting the scattered light in the vicinity of the regular reflection light reflected from the surface on the front side of the sample irradiated with the light by the first illumination unit, by separating the scattered light from the regular reflection light
Implementation Method 3
a first high angle scattered light detection unit for detecting the scattered light scattered in the direction at a higher angle than the direction of the regular reflection light with respect to the normal direction of the sample
Data Source
AI summary
In a method and apparatus for optically inspecting a magnetic disk, irradiating the surface of the sample with a light by rotating and moving the sample in the direction orthogonal to the center axis of the rotation, detecting the regular reflection light from the surface of the sample, detecting the scattered light in the vicinity of the regular reflection light from the surface of the sample by separating the scattered light from the regular reflection light, detecting the scattered light scattered in the direction at a higher angle with respect to the normal direction of the surface of the sample, and detecting the defects by processing the detection signal of the regular reflection light, the detection signal of the scattered light in the vicinity of the regular reflection light, and the detection signal of the scattered light in the high angle direction.