Stereoscopic Hole Depth Measurement With Split FOV Imaging
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Solution Overview
Problem
Existing stereoscopic imaging techniques for determining the depth of milled holes in samples, such as semiconductor wafers, lack the accuracy and precision needed for precise measurements.
Innovation Solution
The method involves forming registration marks on both the top and bottom levels of the milled hole and taking high-resolution, small field of view images at two different tilt angles to capture each registration mark separately, allowing for accurate depth determination using stereoscopic measurement techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large field of view is used to capture both registration marks in a single image, then the imaging process is simpler and faster, but the pixel resolution decreases leading to lower measurement precision
Solution Approach 1:
The patent divides the imaging process into multiple separate images, each capturing a unique registration mark. Instead of attempting to capture both top and bottom registration marks in a single large FOV image, the system takes multiple small FOV images at different tilt angles, where each image focuses on one registration mark. This segmentation allows for higher pixel resolution on each mark while maintaining a manageable imaging workflow through automated processing.
2Measurement precision
If multiple small FOV images are taken at different tilt angles, then the pixel resolution increases improving measurement accuracy, but the number of images and processing steps increases
Solution Approach 1:
The patent performs preliminary actions by taking multiple images at different tilt angles with registration marks already in place before the actual depth measurement calculation. The registration marks are formed in advance on the sample surface, and the multi-angle imaging is performed as a preparatory step to capture the necessary geometric information for subsequent automated depth calculation, reducing the need for repeated measurements.
Solution Approach 2:
The system uses feedback from the captured images to automatically adjust and refine the depth measurement calculation. The stereoscopic processing algorithm analyzes the positions of registration marks across multiple tilt angles, using this feedback information to compute the third coordinate value and verify measurement accuracy, thereby reducing the need for manual intervention or repeated imaging.
3Area of stationary object
If registration marks are captured in overlapping images, then the field of view is larger covering more area, but the pixel resolution for each mark decreases
Solution Approach 1:
The patent applies local quality by optimizing the field of view for each specific registration mark rather than using a uniform large FOV for the entire area. Each small FOV image is tailored to capture one registration mark with high pixel resolution, allocating imaging resources locally to where they are most needed for precise measurement, rather than spreading them out over a larger area.
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 enables highly accurate measurement of the milled hole depth with improved pixel resolution, enhancing the precision of depth calculations.
Implementation Method 1
a ROI on a specimen can be bombarded with ions of Xenon, Gallium or other elements generated by a focused ion beam (FIB) column to erode the surface layer of the specimen in the ROI
Implementation Method 2
a scanning electron microscope (SEM) to study a specific characteristic feature in the wafer
Data Source
AI summary
A method of determining a depth of a hole milled into a first region of a sample, comprising: positioning the sample in a processing chamber having a charged particle beam column; milling a hole in the first region of the sample using a charged particle beam generated by the charged particle beam column; identifying a first registration mark at an upper level of the milled hole; identifying a second registration mark at a lower level of the milled hole; taking a first set of images at a first tilt angle, the first set of images including a first image taken with a field of view that captures the first registration mark but not the second registration mark, and a second image taken with a field of view that captures the second registration mark but not the first registration mark; taking a second set of images at a second tilt angle, different than the first tilt angle, the second set of images including a third image taken with a field of view that captures the first registration mark but not the second registration mark, and a fourth image taken with a field of view that captures the second registration mark but not the first registration mark; using stereoscopic measurement techniques to determine the depth of the hole based on the first and second sets of images.