Optical Foreign Matter Inspection With Multistage Laser Attenuation
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Solution Overview
Problem
Existing optical-type foreign matter inspection devices face challenges in maintaining uniform laser irradiation energy density across the entire inspection region, particularly when rotating samples, due to the difficulty in adjusting illuminance ratios effectively.
Innovation Solution
The device employs a rotary stage with variable optical attenuators of multiple stages to adjust laser beam intensity based on the sample's rotational speed, using a combination of ½ wavelength plates and polarized beam splitters, along with a control system to maintain consistent energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single variable optical attenuator is used to adjust illuminance, then the device complexity is low, but the adjustment ratio is insufficient (about 20 times) to cover the required range (50 times or more) for uniform irradiation energy density across the entire sample surface
Solution Approach 1:
The patent divides the single attenuator function into multiple stages, with each variable optical attenuator handling a portion of the total attenuation range. The first variable optical attenuator adjusts illuminance in a first range, and the second variable optical attenuator adjusts illuminance in a second range, collectively achieving the required 50 times or more adjustment ratio for uniform irradiation energy density across the sample surface.
2Productivity
If the rotation speed of the sample is increased to improve productivity, then the inspection throughput increases, but the laser irradiation energy density becomes non-uniform across different radial positions
Solution Approach 1:
The patent applies different illuminance adjustment strategies to different radial positions on the sample. The variable optical attenuators are controlled to provide position-dependent attenuation, ensuring that the laser irradiation energy density remains uniform across the entire sample surface even when the sample rotates at high speed for improved throughput.
3Measurement precision
If the illuminance of the illumination spot is increased in the outer peripheral portion to compensate for signal decrease, then the detection sensitivity is improved, but the temperature rise of the sample surface becomes excessive
Solution Approach 1:
The patent dynamically adjusts the illuminance parameter of the laser beam using variable optical attenuators to compensate for the decrease in scattered light signal in the outer peripheral portion. By controlling the transmittance of the attenuators, the system increases illuminance where needed to maintain detection sensitivity while managing the overall energy input to prevent excessive temperature rise of the sample surface.
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 ensures uniform laser irradiation energy density across the entire inspection region, enhancing detection sensitivity and reducing variations in foreign matter size detection.
Implementation Method 1
using a combination of ½ wavelength plates and polarized beam splitters
Implementation Method 2
variable optical attenuators of two or more stages configured to adjust a light amount of the laser beam
Implementation Method 3
a sensor configured to detect light scattered or reflected from the surface of the sample
Implementation Method 4
an A/D conversion circuit configured to convert an intensity of light received by the sensor into a digital pixel
Data Source
AI summary
An optical-type foreign matter inspection device that inspects a foreign matter on a surface of a sample includes a rotary stage that is driven to rotate and on which the sample is placed, a laser light source configured to irradiate the surface of the sample with a laser beam, variable optical attenuators of two or more stages configured to adjust a light amount of the laser beam, a sensor configured to detect light scattered or reflected from the surface of the sample, an A/D conversion circuit configured to convert an intensity of light received by the sensor into a digital pixel based on an output signal of the sensor, a data processor configured to receive an output signal of the A/D conversion circuit and coordinate information output from the rotary stage and associate the coordinate information with the output signal of the A/D conversion circuit to output the associated information as detection data, and an attenuator controller configured to control transmittances of the variable optical attenuators based on the coordinate information.