Suspended Membrane Calibration Sample for Charged Particle Beam Systems
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Solution Overview
Problem
Existing calibration samples for charged particle beam systems, such as silicon chips and gold grids, suffer from organic contamination and energy-dependent contrast issues, leading to degraded calibration quality and frequent replacements, and lack the fine features necessary for certain calibrations.
Innovation Solution
A suspended membrane calibration sample is fabricated using a silicon wafer with a patterned layer and buried oxide layer, etched to form a self-supporting membrane over an empty space, providing high contrast and resistance to contamination, independent of electron beam energy and current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon chips with patterned layers are used for calibration, then calibration functionality is provided, but organic contamination builds up on the surface degrading image quality over time
Solution Approach 1:
The patent extracts the calibration patterns from a solid substrate and suspends them in empty space, removing the substrate that would otherwise accumulate contamination. This allows the calibration features to be isolated from contaminating surfaces while maintaining their calibration function.
Solution Approach 2:
The patent uses a thin membrane structure to suspend the calibration patterns. The membrane acts as a support that minimizes contamination accumulation compared to solid substrates, while still providing mechanical support for the calibration features.
2Strength
If gold grids are used for calibration, then structural stability is provided, but fine features and sharp edges necessary for certain calibrations are lacking
Solution Approach 1:
The patent combines the structural stability of suspended membrane technology with high-precision lithographically patterned calibration features. This composite approach achieves both mechanical stability and fine feature resolution that neither gold grids nor simple silicon chips can provide alone.
3Adaptability or versatility
If calibration samples with deposited specimens are used, then natural patterns are provided, but contrast varies with electron beam energy requiring periodic replacement
Solution Approach 1:
The patent creates calibration patterns with locally optimized geometries that produce energy-independent contrast. By carefully designing the shape, size, and arrangement of calibration features, the sample maintains consistent contrast across different electron beam energies.
Data Source
AI summary
One embodiment disclosed relates to a method for fabricating a calibration sample. The method includes lithographically patterning a first side of a wafer with a pattern of a self-supporting membrane, etching the first side of the wafer to form the self-supporting membrane in a layer on the first side, and etching a second side of the wafer to reach the layer so as to suspend the membrane over an empty space. Another embodiment disclosed relates to a charged particle beam system. The system includes a charged particle source, a focusing column and lens assembly, a detector, and a suspended membrane calibration sample. Another embodiment disclosed relates a suspended membrane calibration sample for a charged particle beam system. The calibration sample includes a plurality of calibration patterns in an array, a suspended membrane that is self-supporting and includes the plurality of calibration patterns, and an empty space underneath the membrane.