Compound Objective Lens for SEM Backscattered Electron Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing compound charged particle lenses in Scanning Electron Microscopes (SEMs) cannot effectively distinguish and control the energy and angle distribution of backscattered electrons (BSEs) from different groups, limiting their ability to provide detailed material and topological contrast, especially for magnetizable samples.
Innovation Solution
A configurable compound lens with an electron detector equipped with multiple annular detector areas or a pixilated detector, allowing the ratio of excitation of the coils to control the distribution of BSEs, enabling the lens to focus on the sample while distinguishing between different groups of BSEs based on their impact distance from the axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a compound charged particle lens is used to focus the beam on the sample, then the resolution is improved, but the ability to distinguish and control energy and angle distribution of backscattered electrons is lost
Solution Approach 1:
The detector surface is segmented into multiple annular detector areas (first, second, and third groups) at different radial distances from the symmetry axis. This segmentation allows different groups of backscattered electrons with different energy and angle characteristics to be detected separately, preserving the distribution information that would otherwise be lost in a conventional focused beam system.
Solution Approach 2:
Different regions of the detector surface are assigned different detection functions based on their radial position. The first annular area detects electrons with specific energy-angle characteristics, while the second and third annular areas detect electrons with different characteristics. This local differentiation enables simultaneous preservation of both focusing capability and distribution information.
2Loss of information
If the coil excitation ratio is adjusted to control backscattered electron distribution, then the material and topological contrast is enhanced, but the system complexity increases
Solution Approach 1:
The excitation currents of the first and second coils are varied as adjustable parameters to control the magnetic field distribution and thereby control the distribution of backscattered electrons. By changing these parameters, the system can optimize detection for different material properties and topological features without requiring physical reconfiguration.
Solution Approach 2:
The system employs dynamic control of coil excitations to adaptively adjust the electron beam focusing and backscattered electron distribution according to the specific sample being analyzed. This dynamic adjustment capability allows the system to optimize contrast for different materials and features in real-time.
3Measurement precision
If multiple annular detector areas are used to distinguish different groups of backscattered electrons, then the measurement capability is improved, but the detector complexity increases
Solution Approach 1:
The detector surface is divided into multiple annular areas with different radial distances from the symmetry axis. Each annular area corresponds to a specific group of backscattered electrons with characteristic energy and angle ranges. This segmentation enables differentiation of electron groups while maintaining a relatively simple overall detector structure based on conventional semiconductor or scintillator technology.
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
This configuration allows for enhanced material and topological contrast by selectively focusing and detecting BSEs, providing additional information about the sample's properties and overcoming limitations with magnetizable samples.
Implementation Method 1
a first coil for generating a focusing magnetic field between the first magnetic lens pole and the second magnetic lens pole
Implementation Method 2
a second lens coil for generating a focusing immersion magnetic field between the first magnetic lens pole and the sample position
Implementation Method 3
an electrode with a central hole, the central hole for passing the beam of charged particles through the lens to the sample, the electrode for generating a decelerating electric field between the lens and the sample by applying a voltage difference between the electrode and the sample
Implementation Method 4
the finely focused beam is focused at the sample
Implementation Method 5
the voltage difference of the sample is a predetermined voltage difference
Data Source
AI summary
The invention relates to a compound objective lens for a Scanning Electron Microscope having a conventional magnetic lens excited by a first lens coil, an immersion magnetic lens excited by a second lens coil, and an immersion electrostatic lens excited by the voltage difference between the sample and the electrostatic lens electrode. For a predetermined excitation of the lens, the electron beam can be focused on the sample using combinations of excitations of the two lens coils. More BSE information can be obtained when the detector distinguishes between BSE's (202) that strike the detector close to the axis and BSE's (204) that strike the detector further removed from the axis. By tuning the ratio of the excitation of the two lens coils, the distance from the axis that the BSE's impinge on the detector can be changed, and the compound lens can be used as an energy selective detector.