Confocal Laser Scanning Microscope Focus Adjustment
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Solution Overview
Problem
Optical microscopes face challenges in rapidly and accurately adjusting focus, especially when dealing with semiconductor wafers and transparent materials, due to the need for high magnification and resolution in defect detection, which is hindered by the complexity of achieving a clear focal point.
Innovation Solution
A focusing device for optical microscopes that uses a combination of laser scanning and a confocal-type mechanism, incorporating a wedge mirror, light emitting and receiving units, and a control unit to calculate focus error and adjust the specimen or objective lens position, along with a spatial filter to eliminate out-of-focus light, enabling rapid and accurate focus adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional focus adjustment methods are used, then the optical microscope can achieve focus, but the focus adjustment time is long and the focusing speed is slow
Solution Approach 1:
The patent replaces conventional mechanical focus adjustment methods with a laser scanning-based optical system. A laser beam scans the specimen surface, and the reflected light is detected by photodetectors to generate focus error signals, eliminating the need for slow mechanical movement and manual focusing while dramatically reducing focus adjustment time and increasing focusing speed.
Solution Approach 2:
The system implements automatic focus adjustment by using the specimen's own reflected light as the signal source. The laser scans the specimen, collects reflected light, and the system automatically generates focus error signals to drive the focus motor, enabling self-service focus adjustment without external intervention or complex additional illumination systems.
2Measurement precision
If high magnification is used to improve defect detection accuracy, then measurement precision improves, but the ability to accurately detect the focal point deteriorates
Solution Approach 1:
The patent segments the detected light into in-focus and out-of-focus components using a spatial filter (pinhole aperture). The pinhole blocks out-of-focus light while allowing in-focus light to pass through to the photodetector, enabling accurate focal point detection even at high magnifications where the depth of field is extremely shallow and focal point precision is critical.
3Loss of information
If conventional light receiving methods are used, then the system can detect reflected light, but out-of-focus light interferes with accurate focus detection
Solution Approach 1:
The patent extracts only the in-focus light component from the total reflected light using a spatial filter (pinhole aperture) positioned at the focal plane of a lens. The pinhole physically blocks out-of-focus light while transmitting in-focus light to the photodetector, eliminating signal interference and enabling precise focus detection by taking out only the useful in-focus signal.
Solution Approach 2:
The spatial filter (pinhole aperture) acts as an intermediary between the lens and photodetector. It selectively transmits in-focus light while blocking out-of-focus light, serving as a mediator that cleans the optical signal before it reaches the detector, thereby improving focus detection accuracy without requiring changes to the laser scanning system or photodetector.
4Adaptability or versatility
If the optical microscope is used for transparent materials with small thickness, then the application scope is expanded, but accurate focus adjustment becomes more difficult
Solution Approach 1:
The patent replaces mechanical focus estimation methods with laser scanning-based optical focus detection. The laser beam scans the transparent material surface, and the reflected light intensity variations are detected by photodetectors to generate precise focus error signals, enabling accurate focus adjustment on transparent materials with small thickness where mechanical methods fail due to inability to detect surface features.
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 solution significantly reduces focus adjustment time and improves accuracy by using laser scanning and confocal-type mechanisms to determine the correct focal point, even with transparent materials, enhancing defect detection in semiconductor manufacturing.
Implementation Method 1
first and second light receiving units configured to detect an amount of laser light reflected from the surface of the specimen
Implementation Method 2
a spatial filter configured to eliminate out-of-focus light from light beams reflected from the surface of the specimen and to detect an amount of in-focus light
Data Source
AI summary
A focusing device for an optical microscope may include a light emitting unit configured to emit laser light having a specific wavelength, a wedge mirror configured to enable the emitted laser light to be incident on a plurality of locations of a surface of a specimen, first and second light receiving units configured to detect an amount of laser light reflected from the surface of the specimen, a spatial filter configured to eliminate out-of-focus light from light beams reflected from the surface of the specimen and to detect an amount of in-focus light, and a control unit configured to generate a control signal used to carry out focus adjustment of the optical microscope using a plurality of light-amount information detected by the first and second light receiving units and the spatial filter.