Cathodoluminescence Mirror Alignment via Reference Marks
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Solution Overview
Problem
Current methods for aligning cathodoluminescence (CL) mirrors in electron microscopes are time-consuming and unreliable, especially when dealing with samples that have time and space variant CL properties, leading to significant losses in CL light collection and fidelity of information.
Innovation Solution
The implementation of automated alignment procedures, such as MirrorfeatureXY and MirrorfeatureZ, which utilize positional reference marks and precise actuation mechanisms to quickly align the CL mirror with respect to the electron beam and sample in the X, Y, and Z axes, without relying on CL properties, using a combination of electromechanical actuators and control systems to adjust the mirror and sample stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual alignment adjustments are performed to maximize CL intensity, then alignment precision can be improved, but alignment time increases significantly
Solution Approach 1:
The patent applies preliminary action by providing pre-calibrated reference marks on the sample stage with known positions relative to the optical axis. These reference marks are prepared in advance, allowing the alignment system to quickly determine the correct stage position without time-consuming manual adjustments. The control system automatically calculates the required stage displacement based on the detected reference mark position, enabling rapid alignment.
Solution Approach 2:
The patent replaces manual mechanical alignment adjustments with an automated optical-detection-based system. Instead of relying on operators to visually assess and mechanically adjust the stage position, the system uses a camera or detector to optically detect the reference mark position, and the control system automatically computes and executes the necessary stage displacement, substituting human mechanical adjustment with automated sensing and control.
2Measurement precision
If CL intensity maximization methods are used for alignment, then alignment accuracy improves, but the method fails for samples with time and space variant CL properties
Solution Approach 1:
The patent introduces an intermediary reference mark system that mediates between the sample stage and the alignment detection system. These reference marks are distinct from the actual sample material and provide consistent, stable alignment features that do not depend on the sample's CL properties. The reference marks serve as a universal intermediary that works with all sample types, including those with time and space variant CL properties that would otherwise be incompatible with CL-intensity-based alignment methods.
3Measurement precision
If the e-beam is moved in the XY plane for alignment, then mirror alignment can be achieved, but the e-beam focus degrades
Solution Approach 1:
The patent inverts the traditional alignment approach by keeping the e-beam fixed at the center of the field of view and instead moving the sample stage to achieve alignment. Normally, one would move the e-beam to align with the mirror, but this degrades focus. The inverted approach moves the stage (carrying the sample and reference marks) to the correct position, achieving mirror alignment while maintaining optimal e-beam focus at the field center.
4Productivity
If automated alignment procedures are implemented, then alignment speed increases, but system complexity increases
Solution Approach 1:
The patent applies universality by designing the reference mark system to serve multiple functions: it provides alignment reference features, enables automatic position detection, and works with various sample types and e-beam conditions. The same reference marks and detection system are used regardless of the specific sample being analyzed, eliminating the need for sample-specific alignment procedures and reducing overall system complexity despite the automation.
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
These methods enable rapid and precise alignment, reducing alignment time from minutes to seconds, improving the fidelity of CL light collection and allowing for efficient examination of multiple sample locations and e-beam voltages, even for samples that do not emit CL light reliably at every position.
Implementation Method 1
When a high energy electron or ion beam (e-beam) strikes a sample, photons can be emitted depending on the sample material. The emitted photons are also known as cathodoluminescence (CL).
Implementation Method 2
One way to collect CL is via a collection mirror, often with a paraboloid or ellipsoid shape, located on axis with the e-beam and either above (more typically) or below the sample or both.
Data Source
AI summary
Systems and methods for automated alignment of cathodoluminescence (CL) optics in an electron microscope relative to a sample under inspection are described. Accurate placement of the sample and the electron beam landing position on the sample with respect to the focal point of a collection mirror that reflects CL light emitted by the sample is critical to optimizing the amount of light collected and to preserving information about the angle at which light is emitted from the sample. Systems and methods are described for alignment of the CL mirror in the XY plane, which is orthogonal to the axis of the electron beam, and for alignment of the sample with respect to the focal point of the CL mirror along the Z axis, which is coincident with the electron beam.