SEM Column Angle Calibration for Precise Stereoscopic Depth Measurement
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Solution Overview
Problem
Existing stereoscopic imaging techniques for determining the depth of milled holes in electronic structures lack precision and accuracy, relying on assumed tilt and rotation angles of the SEM column.
Innovation Solution
The method involves positioning a test structure with known dimensions in a processing chamber and determining the actual tilt and rotation angles using vector projection and spherical coordinates, which are then used for precise stereoscopic measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If assumed tilt and rotation angles are used for stereoscopic measurements, then the measurement process is simple, but the measurement precision deteriorates
Solution Approach 1:
The patent changes the parameters used for measurement by replacing assumed tilt and rotation angles with empirically determined angles. The system captures images at multiple known tilt angles, calculates actual tilt and rotation angles from measured distances, and uses these corrected angles for stereoscopic measurements, thereby improving measurement precision without significantly complicating the process
Solution Approach 2:
The patent replaces the mechanical assumption of precise tilt/rotation angles with an optical/mathematical system. Instead of relying on mechanical positioning accuracy, the system uses image capture at multiple angles, vector projection mathematics, and spherical coordinate calculations to determine actual angles, substituting mechanical precision requirements with computational geometry
2Device complexity
If calibrated tilt and rotation angles are assumed to be known, then the device complexity is reduced, but the measurement precision deteriorates
Solution Approach 1:
The patent performs preliminary calibration by capturing images of a test structure at multiple known tilt angles before actual measurements. This preliminary action determines the actual tilt and rotation angles that will be used for subsequent stereoscopic measurements, ensuring precision without adding complexity to the measurement device itself
Solution Approach 2:
The patent introduces a test structure with known dimensions as an intermediary element. This test structure serves as a reference object that enables calculation of actual tilt and rotation angles through vector projection, acting as a mediator between the imaging system and the measurement process without requiring direct modification of the imaging device
Data Source
AI summary
A method of determining a depth of a feature formed in a first region of a sample, by: positioning a test structure with known dimensions in a processing chamber having a charged particle column tilted at a first tilt angle and first rotational angle; determining the first tilt angle and first rotational angle by: taking an image of the test structure with the charged particle column tilted at the first tilt angle and the first rotational angle, measuring, based on the image, distances between multiple edges of the test structure aligned with each other along a vector, determining ratios between the measured distances, and determining a calculated tilt angle and a calculated rotational angle of charged particle column from the ratios and the known dimensions of the structure; transferring the test structure out of the processing chamber and positioning the sample in the processing chamber such that the first region is under a field of view of the charged particle column; taking a first image of the feature with the column tilted at the first tilt angle and first rotational angle and taking a second image of the feature with the column is tilted at a second tilt angle, different than the first tilt angle, and a second rotational angle; and using stereoscopic measurement techniques to determine the depth of the feature based on the first and second images and the calculated tilt angle and calculated rotational angle.