Rotating Wafer Brightfield Inspection With Synchronized Line Cameras
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Solution Overview
Problem
Current brightfield inspection methods for circular rotating wafers in semiconductor manufacturing face challenges due to non-uniform thickness and the need for precise focus adjustment, as traditional TDI cameras struggle with integrating pixel data across rows and require individual focus measurement at each point, leading to inefficiencies in inspection time and sensitivity.
Innovation Solution
A method and system utilizing a plurality of line cameras synchronized with a rotating wafer, employing time and space synchronization, auto-correlation, and a light modulator to integrate images and achieve in-focus inspection, including a spoke pattern arrangement and artificial neural networks for curvature matching and focus adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional TDI cameras are used to scan the wafer in rectangular swathes with linear motion, then the inspection mechanism can identify defects with nm level precision, but the time taken for inspection of the whole wafer is approximately 153 minutes
Solution Approach 1:
The patent transitions from rectangular linear scanning to circular rotational scanning, matching the wafer's circular geometry. The wafer rotates on a turntable while line cameras capture images along the circular path, enabling continuous scanning without stage repositioning and reducing inspection time while maintaining nm-level defect detection precision through synchronized circular motion
Solution Approach 2:
The patent implements continuous rotational scanning where the wafer rotates continuously on a turntable while line cameras continuously capture images. This eliminates the stop-and-go nature of linear scanning with stage repositioning, maintaining continuous inspection action and significantly reducing the 153-minute inspection time to a much shorter duration
2Adaptability or versatility
If a circular rotating wafer is scanned with TDI camera, then the scanning can be performed on circular wafer, but each pixel in a first column observes a different scene and pixels cannot be integrated across rows
Solution Approach 1:
The patent uses dynamic synchronization where the turntable rotates at a controlled speed and the line cameras are synchronized to capture images at specific angular positions. The rotation speed and camera exposure timing are dynamically coordinated so that corresponding pixels across multiple line cameras observe the same scene, enabling proper integration while maintaining circular wafer compatibility
Solution Approach 2:
The patent implements feedback control where the rotation position of the turntable is continuously monitored and used to trigger camera exposures at precise moments. This feedback mechanism ensures that images captured by multiple line cameras are properly synchronized in time and space, allowing pixel integration across rows while maintaining adaptability to circular wafer geometry
3Measurement precision
If focus of the wafer is measured at each inspection point, then in-focus images can be obtained, but due to non-uniformities in thickness of chuck and wafer, a same focus does not work at all points
Solution Approach 1:
The patent divides the wafer surface into multiple radial zones and measures focus at representative points in each zone rather than at every single inspection point. This segmentation approach captures the non-uniform thickness variations across different radial positions while reducing the overall number of measurements needed, balancing focus accuracy with reduced complexity
Solution Approach 2:
The patent applies different focus settings to different radial zones of the wafer based on local thickness characteristics. Instead of using a single global focus setting, the system adjusts focus parameters locally for each zone to account for non-uniform chuck and wafer thickness, achieving accurate focus at each location without requiring measurements at every inspection point
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
Enhances inspection efficiency by reducing noise, increasing sensitivity, and ensuring uniform focus across the wafer surface, thereby improving the speed and accuracy of defect detection in circular rotating wafers.
Implementation Method 1
The light modulator includes a two-dimensional (2D) micro lens or a spatial light modulator (SLM)
Data Source
AI summary
Systems and methods for brightfield inspection of a circular rotating wafer are provided. A method includes: acquiring a plurality of images of a circular wafer, that is rotating, by using a plurality of line cameras; obtaining a plurality of synchronized images, based on the plurality of images, by synchronizing a motion of the circular wafer, that is rotating, with at least one line camera from among the plurality of line cameras; obtaining a single wafer map by integrating together the plurality of synchronized images; obtaining an in-focus image of the single wafer map while the circular wafer is moving; and performing brightfield inspection of the circular wafer based on the in-focus image of the single wafer map.