Specimen Focus Map Generation for 3D Inspection
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Solution Overview
Problem
In semiconductor manufacturing, maintaining accurate focus during specimen scans is challenging due to non-flat specimens and varying flatness, leading to focus tracking errors and inaccuracies in defect detection and metrology, especially with 3D structures where existing autofocus methods often mis-track features, resulting in out-of-focus images and missed defects.
Innovation Solution
A system and method that generate a focus map by scanning pre-focus swaths across a specimen, interpolating the data to determine best focus settings, and storing these settings for use during the scan, ensuring consistent in-focus conditions across the inspection area using an output acquisition subsystem and computer subsystems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional autofocus methods are used to track the top surface during scanning, then the system can maintain focus on the uppermost surface, but it fails to maintain focus on underlying features causing out-of-focus images and missed defects
Solution Approach 1:
The system performs preliminary scanning at multiple z-positions to collect focus metric data before the actual inspection scan. This pre-scan data is used to generate a focus map that predicts the best focus position at each x-y location, allowing the system to maintain accurate focus on underlying features rather than just the top surface during the inspection scan.
Solution Approach 2:
The system extends the traditional two-dimensional scanning (x-y plane) by incorporating the z-dimension (focus depth) as a third dimension. By scanning at multiple z-positions and creating a three-dimensional focus map, the system can determine the optimal focus position for features at different depths, not just the top surface, thereby improving defect detection reliability for embedded features.
2Productivity
If the scanning speed is increased to improve productivity, then more wafers can be inspected per unit time, but focus tracking errors increase leading to out-of-focus images
Solution Approach 1:
The system performs preliminary scanning at multiple z-positions to collect focus metric data before the actual inspection scan. This pre-scan data is used to generate a focus map that predicts the best focus position at each x-y location, allowing the system to maintain accurate focus on underlying features rather than just the top surface during the inspection scan.
Solution Approach 2:
The system extends the traditional two-dimensional scanning (x-y plane) by incorporating the z-dimension (focus depth) as a third dimension. By scanning at multiple z-positions and creating a three-dimensional focus map, the system can determine the optimal focus position for features at different depths, not just the top surface, thereby improving defect detection reliability for embedded features.
3Measurement precision
If multiple z-positions are scanned to improve focus accuracy, then better focus settings can be determined, but the scanning time increases reducing productivity
Solution Approach 1:
The system performs preliminary scanning at multiple z-positions to collect focus metric data before the actual inspection scan. This pre-scan data is used to generate a focus map that predicts the best focus position at each x-y location, allowing the system to maintain accurate focus on underlying features rather than just the top surface during the inspection scan.
Solution Approach 2:
The system extends the traditional two-dimensional scanning (x-y plane) by incorporating the z-dimension (focus depth) as a third dimension. By scanning at multiple z-positions and creating a three-dimensional focus map, the system can determine the optimal focus position for features at different depths, not just the top surface, thereby improving defect detection reliability for embedded features.
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 improves focus tracking and accuracy, reducing the likelihood of missed defects and enhancing the reliability of inspection and metrology processes by maintaining consistent focus throughout the scanned area, even with complex 3D structures.
Implementation Method 1
an output acquisition subsystem configured to direct energy to a specimen, to detect energy from the specimen, and to generate output responsive to the detected energy
Data Source
AI summary
Methods and systems for determining focus settings for use in a specimen scan are provided. One method includes generating a focus map defined as values of best focus as a function of position on a specimen using output generated in one or more pre-focus swaths scanned on the specimen by an output acquisition subsystem configured to direct energy to a specimen, to detect energy from the specimen, and to generate output responsive to the detected energy. The method also includes interpolating the focus map to generate focus settings for a scan performed on the specimen during a process and storing information for the generated focus settings for use in the scan performed on the specimen during the process.