Dual Mechanical Stage Wafer Scanning for Defect Review Speed
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Solution Overview
Problem
The defect review process for wafers is slow due to the time required for the heavy mechanical stage to accelerate and decelerate, especially when scanning multiple suspected defects, which limits the efficiency of the inspection process.
Innovation Solution
A system comprising a first mechanical stage and a second mechanical stage, where the second stage introduces additional movements to enhance the field of view and image acquisition of the first stage, allowing for constant velocity movements along scan lines and optimizing the scan pattern to increase the time a defect is within the optics' view, thereby accelerating the defect review process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a heavy mechanical stage is used to support the wafer for high-resolution scanning electron microscope inspection, then the stability and precision of the inspection are improved, but the acceleration and deceleration time increases significantly, reducing productivity
Solution Approach 1:
The mechanical stage system is segmented into two independent stages: a first mechanical stage for coarse positioning and scanning movements, and a second mechanical stage for fine positioning adjustments. This segmentation allows each stage to be optimized for its specific function, with the first stage handling high-speed scanning and the second stage providing precise defect positioning, thereby resolving the contradiction between inspection precision and review speed
Solution Approach 2:
The second mechanical stage is nested on top of the first mechanical stage, creating a hierarchical structure where the lighter second stage performs fine adjustments while the heavier first stage handles gross movements. This nesting arrangement allows the system to achieve both high precision (through the second stage) and high speed (through the first stage's faster acceleration and deceleration capabilities)
2Measurement precision
If the mechanical stage stops at each suspected defect location for image acquisition, then the inspection accuracy is improved, but the total inspection time increases due to repeated acceleration and deceleration cycles
Solution Approach 1:
The system performs preliminary coarse positioning using the first mechanical stage to bring the defect into the approximate field of view before the optics begin image acquisition. This preliminary action allows the heavier stage to be in motion rather than stopping completely, significantly reducing the time penalty associated with acceleration and deceleration cycles while still maintaining sufficient image quality
Solution Approach 2:
The system transitions from a static inspection approach (stopping at each defect location) to a dynamic approach where the first mechanical stage continues moving during image acquisition. The second mechanical stage dynamically adjusts to track the defect position, allowing continuous scanning without complete stops and thereby reducing overall inspection time while maintaining measurement precision
Data Source
AI summary
A method for scanning an object, the method may include moving an object by a first mechanical stage that follows a first scan pattern; introducing multiple movements, by a second mechanical stage, between the object and the first mechanical stage while the first mechanical stage follows the first scan pattern; and obtaining, by optics, images of multiple suspected defects while the first mechanical stage follows the first scan pattern; wherein a weight of the first mechanical stage exceeds a weight of the second mechanical stage.