TDI Sensor Beam Control for Inspection Luminance Uniformity
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Solution Overview
Problem
Current inspection systems using TDI sensors face challenges in maintaining consistent image data quality due to variations in the moving speed of the inspection target, leading to uneven luminance and reduced accuracy in defect type determination.
Innovation Solution
The implementation of a prevention module that controls the arrival of the beam or secondary charged particles at the TDI sensor during the integration period, ensuring a constant exposure time and reducing uneven charge-up, along with a normalization module that adjusts image data based on the time required for the movable unit to move a predetermined distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inspection target is moved at high speed through the beam irradiation position, then productivity is improved, but the moving speed variations cause uneven luminance and reduce measurement precision
Solution Approach 1:
The system performs preliminary actions by resetting the TDI sensor and controlling beam irradiation timing before each integration period. The control unit resets the TDI sensor before the integration period starts and controls the beam to be irradiated only during the integration period, ensuring consistent exposure conditions regardless of stage speed variations.
Solution Approach 2:
The system implements periodic action by using discrete integration periods with regular resetting. The TDI sensor is reset before each integration period, and the beam irradiation is controlled to occur only during these periodic intervals, creating consistent measurement cycles that eliminate cumulative errors from speed variations.
2Measurement precision
If the beam is continuously irradiated during TDI sensor operation, then measurement precision is maintained, but uneven charge-up occurs due to speed variations
Solution Approach 1:
The control unit performs preliminary resetting of the TDI sensor before each integration period begins. This preliminary action clears any residual charge from previous measurements, ensuring that each integration period starts with a clean state and preventing uneven charge-up accumulation.
Solution Approach 2:
The system uses periodic integration periods with regular resetting intervals. The TDI sensor is reset before each period and the beam is controlled to irradiate only during these periodic windows, creating consistent charge-up patterns that eliminate unevenness caused by speed variations.
3Measurement precision
If the TDI sensor integrates secondary charged particles over extended periods, then measurement precision improves, but the system becomes more sensitive to speed variations
Solution Approach 1:
The control unit resets the TDI sensor before each integration period as a preliminary action. This ensures that each integration starts from a known zero state, allowing consistent signal integration regardless of how long the overall inspection process takes or what the stage speed variations are.
Solution Approach 2:
The system implements periodic integration periods with regular resetting. By confining beam irradiation to these periodic intervals and resetting the sensor before each period, the system achieves consistent integration accuracy that is independent of stage speed variations occurring between or during periods.
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 enhances the accuracy of inspection by minimizing the impact of moving speed variations on image data quality and improves the reliability of defect type determination by maintaining consistent luminance and exposure times.
Implementation Method 1
irradiating either of a charged particle and an electromagnetic wave as a beam onto an inspection target
Implementation Method 2
a secondary charged particle which is obtained according to the properties of a surface of an inspection target
Implementation Method 3
integrating an amount of secondary charged particles in a predetermined direction through a time delay integration to sequentially transfer the integrated amount of secondary charged particles
Data Source
AI summary
An inspection system includes a primary optical system configured to irradiate a charged particle or an electromagnetic wave as a beam, a movable unit configured to hold an inspection target and move the target through a position where the beam is irradiated, and a TDI sensor configured to integrate an amount of secondary charged particles in a predetermined direction to sequentially transfer the integrated amount. The secondary charged particles are obtained by irradiating the beam onto the target while moving the movable unit in the predetermined direction. The inspection system further includes a prevention module configured to prevent an arrival of the beam at the target side or an arrival of the secondary charged particles at the TDI sensor during a time period from one transfer to the following transfer after the elapse of a predetermined length of time from the one transfer and until the following transfer.