Behind-the-lens Dark Field Detector for SEM Topography
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Solution Overview
Problem
Conventional scanning electron microscope (SEM) dark field detection systems are incompatible with final lens arrangements that use magnetic and/or electric fields, leading to reduced collection efficiency and poor control over polar angle discrimination, resulting in inferior dark-field contrast.
Innovation Solution
A behind-the-lens-dark-field (BLDF) configuration using a cooperative arrangement of a ring-like element, conductive grids, and a dodecapole deflector to separate and focus scattered electrons, improving dark field purity, flexibility, and signal-to-noise ratio by optimizing electron beam separation and detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a below-the-lens configuration is used for dark field detection, then topography sensitivity is improved, but compatibility with final lens arrangements using magnetic and/or electric fields deteriorates
Solution Approach 1:
The patent inverts the conventional below-the-lens configuration by placing the detector behind the objective lens. This positional inversion allows the detector to receive scattered electrons after they have passed through the final lens, thereby maintaining compatibility with magnetic and/or electric fields used in the lens while still achieving dark field imaging capability.
Solution Approach 2:
The patent introduces a beam separator as an intermediary component between the objective lens and the detector. This beam separator selectively transmits scattered electrons to the detector while blocking the primary electron beam, enabling the detector to function properly in the behind-the-lens configuration without interference from the primary beam.
2Quantity of substance
If a below-the-lens configuration is used for dark field detection, then collection efficiency is improved, but control over polar angle discrimination deteriorates
Solution Approach 1:
The patent employs a variable extraction field that can be dynamically adjusted to control the polar angle acceptance of the detector. By varying the extraction field strength, the system can optimize between collecting more scattered electrons (higher efficiency) and maintaining stricter polar angle discrimination, providing dynamic control over the detection parameters.
3Adaptability or versatility
If a behind-the-lens configuration is used for dark field detection, then compatibility with final lens arrangements is improved, but dark field contrast deteriorates
Solution Approach 1:
The patent segments the detector into multiple detection elements arranged to receive scattered electrons from different angular ranges. This segmentation allows selective detection of electrons at specific polar angles, thereby restoring dark field contrast in the behind-the-lens configuration by emphasizing signals from higher polar angles while suppressing lower angle contributions.
Solution Approach 2:
The patent applies different functions to different parts of the detection system. The beam separator selectively transmits only scattered electrons to specific detector regions, while the variable extraction field locally modulates the electron trajectories. This local quality differentiation ensures that only electrons with the desired angular characteristics reach the detection elements, maintaining dark field contrast.
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
Enhances dark field imaging by improving contrast, flexibility, and signal-to-noise ratio, allowing for better topographical imaging with reduced charging artifacts and increased imaging throughput.
Implementation Method 1
A behind-the-lens-dark-field (BLDF) configuration using a cooperative arrangement of a ring-like element, conductive grids, and a dodecapole deflector to separate and focus scattered electrons
Implementation Method 2
The middle element of the three elements (the two biased grids and the conductive ring) may be defined as the electron lens grid
Data Source
AI summary
An electron beam apparatus is configured for dark field imaging of a substrate surface. Dark field is defined as an operational mode where the image contrast is sensitive to topographical features on the surface. A source generates a primary electron beam, and scan deflectors are configured to deflect the primary electron beam so as to scan the primary electron beam over the substrate surface whereby secondary and/or backscattered electrons are emitted from the substrate surface, said emitted electrons forming a scattered electron beam. A beam separator is configured to separate the scattered electron beam from the primary electron beam. The apparatus includes a cooperative arrangement which includes at least a ring-like element, a first grid, and a second grid. The ring-like element and the first and second grids each comprises conductive material. A segmented detector assembly is positioned to receive the scattered electron beam after the scattered electron beam passes through the cooperative arrangement. Other embodiments, aspects and features are also disclosed. The apparatus is configured to yield good topographical contrast, high signal to noise ratio, and to accommodate a variety of scattered beam properties that result from different primary beam and scan geometry settings.