TDI Sensor Feedback Control for Photomask Inspection Image Clarity
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Solution Overview
Problem
Existing photomask inspection apparatuses face issues with image blurring and distortion due to mismatched stage moving speed and accumulating time, leading to inaccurate defect detection, especially when the stage moves in the pixel direction perpendicular to the accumulating direction.
Innovation Solution
The apparatus includes a moving amount detecting unit to correct the stage movement in the pixel direction by calculating and adjusting the drive amount of the sensor drive unit based on detected moving amounts, ensuring synchronized image capture and preventing blurring, utilizing a TDI sensor with feedback control to maintain accurate defect inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the stage moves in the pixel direction perpendicular to the accumulating direction, then the inspection coverage is improved, but image blurring and distortion occur due to mismatched stage speed and accumulating time
Solution Approach 1:
The patent employs a feedback control mechanism where the actual stage position is continuously monitored and compared with the expected position based on stage speed and accumulating time. When deviations are detected, the system adjusts the stage speed or accumulating time to correct the mismatch, thereby preventing image blurring and distortion while maintaining inspection coverage
Solution Approach 2:
The system dynamically adjusts the stage speed or sensor accumulating time based on real-time position feedback. This dynamic adjustment allows the stage to move in the pixel direction for expanded inspection coverage while maintaining synchronized image capture to prevent blurring, resolving the contradiction between productivity and manufacturing precision
2Productivity
If the stage speed is increased to improve inspection efficiency, then productivity is improved, but image blurring occurs due to mismatch with sensor accumulating time
Solution Approach 1:
The feedback control unit continuously monitors the actual stage position and compares it with the expected position calculated from stage speed and accumulating time. When speed increases cause position mismatches, the system provides feedback to adjust either the stage speed or the sensor accumulating time, ensuring image accuracy is maintained even at higher inspection efficiencies
Solution Approach 2:
The system changes operational parameters dynamically - specifically adjusting the stage speed or the sensor accumulating time based on the inspection requirements and actual stage performance. This parameter adjustment allows the system to operate at higher speeds for improved productivity while maintaining the synchronized capture needed for image accuracy
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 enables precise defect inspection by maintaining image clarity and contrast, ensuring accurate detection of patterns on photomasks and semiconductor wafers by synchronizing stage movement with image accumulation, thereby improving inspection accuracy.
Implementation Method 1
a TDI (Time Delay and Integration) sensor 27 to output image data D1 of the photomask M
Data Source
AI summary
An inspecting apparatus includes an illuminating optical system which irradiates irradiation light onto an object to be inspected, an object placing stage which moves the object along a first direction, an accumulative sensor which converts a transmitted image of the object into an electric signal, a sensor drive unit which moves the accumulative sensor in the irradiation direction and a second direction crossing the first direction, a moving amount detecting unit which detects a moving amount of the object placing stage in the second direction, a control unit which controls a drive amount of the sensor drive unit in the second direction on the basis of the moving amount in the second direction detected by the moving amount detecting unit, and a data comparing unit which compares the transmitted image data of the object with a reference data to detect a defect of the object.