Multi-Beam SEM Closed-Loop Control for Beamlet Stability
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Solution Overview
Problem
Existing multi-beam charged particle devices face challenges with unstable imaging conditions due to charging effects and inter-beam crosstalk, leading to reduced signal strength and increased cross talk, particularly when dealing with large numbers of secondary beamlets and fast raster speeds.
Innovation Solution
A closed-loop control process is implemented to stabilize the pattern of secondary beamlets by using matrix multiplication techniques and affine transformations, adjusting beam positions to align with a setpoint, and distributing computation between FPGA logic and microprocessors to achieve low-latency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of secondary beamlets is increased to improve imaging coverage and resolution, then imaging quality is improved, but inter-beam crosstalk increases and signal strength decreases
Solution Approach 1:
The patent divides the detection task into multiple independent pixel regions, each assigned to detect secondary electrons from a specific primary beamlet. This segmentation allows simultaneous detection of multiple beamlets while maintaining individual signal integrity, reducing crosstalk between beams.
Solution Approach 2:
The patent implements a feedback mechanism where the detected secondary electron signals are used to adjust and optimize the imaging parameters. The system continuously monitors the signal strength and crosstalk levels, and adjusts beam positioning or detection parameters to maintain optimal imaging quality while minimizing harmful effects.
2Productivity
If the raster speed is increased to improve throughput, then productivity is improved, but imaging stability deteriorates due to charging effects
Solution Approach 1:
The patent applies preliminary compensation for charging effects by pre-adjusting beam parameters or detection settings based on expected charging conditions at different raster speeds. This allows the system to maintain imaging stability even when operating at high throughput speeds.
Solution Approach 2:
The patent implements dynamic adjustment of imaging parameters based on the actual raster speed and charging conditions. The system can adaptively modify beam current, detection sensitivity, or scanning patterns in real-time to maintain stable imaging conditions while maximizing throughput.
3Measurement precision
If real-time control of secondary beamlet pattern is implemented to reduce crosstalk, then imaging quality is improved, but computational complexity increases
Solution Approach 1:
The patent extracts and processes only the essential information needed for beamlet pattern control from the detected signals. By focusing computation on critical parameters rather than processing all raw data, the system achieves real-time control with reduced computational complexity.
Solution Approach 2:
The patent replaces complex mechanical or electronic control systems with computational algorithms that can be executed efficiently in software or firmware. This substitution reduces hardware complexity while maintaining the ability to perform real-time pattern control for minimizing crosstalk.
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
The solution maintains stable imaging conditions, reduces inter-beam crosstalk, and ensures high-quality imaging even with large numbers of secondary beamlets and fast raster speeds, enhancing reliability and throughput.
Implementation Method 1
The plurality of J individual primary beamlets are focused on a surface of a sample to be examined by way of an objective lens system
Implementation Method 2
During the illumination of the sample—with the primary beamlets, interaction products, for example secondary electrons or backscattered electrons, emanate from the surface of the wafer
Implementation Method 3
The secondary beamlets can be focused by the secondary electron optical imaging system and focus points of the secondary beamlets are formed on an image plane
Data Source
AI summary
Various examples generally pertain to closed-loop control of one or more parameters of a multi-beam charged particle imaging system, e.g., a multi beam scanning electron microscope, mSEM. A pattern of secondary beamlets can be stabilized. A focal position can be stabilized. According to examples, fast algorithms are facilitated by a field-programmable gated array, FPGA, logic.