Die-to-Die Focus Correction for Semiconductor Inspection
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Solution Overview
Problem
Existing autofocus techniques in semiconductor inspection systems fail to accurately maintain focus between dies, leading to false defect detection and missed defects due to relative die-to-die focus errors, which are exacerbated by the finite speed of focus adjustment systems and pattern effects.
Innovation Solution
A method that constructs an initial focus trajectory using confocal targets and generates a corrected z offset vector by averaging focus errors across multiple dies, ensuring consistent focus settings across die positions, thereby minimizing relative die-to-die focus errors and improving defect detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional autofocus techniques are used to control focus during inspection, then the focus adjustment speed is limited by system constraints, but relative die-to-die focus errors increase leading to false defect detection
Solution Approach 1:
The system performs preliminary autofocus measurements on multiple dies before the actual inspection scan. These measurements are used to construct a corrected z offset vector that compensates for focus variations across different die positions. By pre-characterizing the focus trajectory and applying corrections beforehand, the system eliminates the need for slow real-time focus adjustments during scanning, thereby maintaining both high speed and high reliability in defect detection
Solution Approach 2:
The system implements a feedback mechanism where autofocus data collected from multiple dies is analyzed to generate correction vectors. These correction vectors are then applied to adjust the focus trajectory for subsequent inspection. The feedback loop continuously refines the focus compensation based on measured die-to-die variations, ensuring consistent focus across all dies without requiring slow mechanical adjustments during the actual inspection process
2Measurement precision
If focus settings are adjusted for each die position in real-time, then focus accuracy between dies improves, but inspection throughput decreases due to finite adjustment speed
Solution Approach 1:
The system pre-measures focus positions on multiple dies and constructs a corrected z offset vector before the actual inspection. This preliminary characterization of focus variations allows the system to apply computational corrections rather than mechanical adjustments during scanning, thereby maintaining high focus accuracy across all dies while preserving inspection throughput
Solution Approach 2:
The system replaces mechanical focus adjustment mechanisms with a computational approach. Instead of physically moving the focus mechanism to adjust for each die position, the system uses a corrected z offset vector to computationally compensate for focus variations. This substitution of mechanical adjustment with computational correction eliminates the throughput penalty associated with finite mechanical adjustment speeds while maintaining high focus accuracy
3Measurement precision
If multiple autofocus measurements are taken across different dies, then die-to-die focus variations are detected, but data processing complexity increases
Solution Approach 1:
The system applies local quality by generating individual z offset correction vectors for each die based on its specific focus measurements. Each die's focus characteristics are independently characterized and corrected, allowing for precise local compensation of focus variations while maintaining a systematic approach to data processing
Solution Approach 2:
The system transforms the raw autofocus measurement data into corrected z offset parameters that can be directly applied during inspection. By changing the parameter representation from raw measurements to correction vectors, the system simplifies the data processing required for focus compensation while maintaining high measurement precision
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 significantly reduces false defect detection and improves the accuracy of die-to-die inspection by ensuring consistent focus across die positions, thereby enhancing the reliability of semiconductor defect detection.
Implementation Method 1
locating a plurality of confocal targets that are distributed across the first swath, obtaining a focus setting for each confocal target
Data Source
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AI summary
Disclosed are methods and apparatus for detecting defects in a semiconductor sample having a plurality of identically designed areas. An inspection tool is used to construct an initial focus trajectory for a first swath of the sample. The inspection tool is then used to scan the first swath by following the initial focus trajectory for the first swath while collecting autofocus data. A z offset measurement vector for each identically designed area in the first swath is generated based on the autofocus data. A corrected z offset vector is constructed for inspection of the first swath with the inspection tool. Constructing the corrected z offset vector is based on combining the z offset measurement vectors for two or more of the identically designed areas in the first swath so that the corrected z offset vector specifies a same z offset for each set of same positions in the two or more identically designed areas.