Objective Lens Crossovers for Electron Beam Detection
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Solution Overview
Problem
Existing electron beam devices face challenges in detecting secondary electrons with low energy, leading to a 'detection hole' in images and limited working distance, especially when using primary electron beams with energies below 100 eV, due to the interaction with the primary electron beam's acceleration voltage and magnetic fields.
Innovation Solution
The method involves generating multiple crossovers in the objective lens to separate the trajectories of primary and secondary electrons, allowing for effective detection of secondary electrons at both low and high working distances, using a magnetic unit that creates a first crossover before the object and a second crossover on the object surface, and optionally using a corrector to correct aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a detector with a large opening is used to detect secondary electrons, then the detection efficiency is improved, but the spatial resolution deteriorates due to the detection hole in the middle
Solution Approach 1:
The patent segments the electron beam path by creating multiple crossovers at different positions. The first crossover is formed before the object and the second crossover is formed at the object surface, allowing separate detection paths for primary and secondary electrons. This segmentation enables the detector to receive secondary electrons without blocking the primary electron beam, eliminating the detection hole problem while maintaining spatial resolution.
Solution Approach 2:
The patent introduces a temporal dimension to the detection process by using pulse-shaped extraction voltages. The extraction voltage is applied in synchronization with the electron beam pulses, creating time-gated detection windows. This allows the detector to distinguish between primary and secondary electrons based on their arrival times, improving detection efficiency without compromising spatial resolution.
2Object-affected harmful factors
If the primary electron beam energy is reduced below 100 eV to avoid object destruction, then the object safety is improved, but the secondary electron detection becomes difficult due to trajectory overlap with primary electrons
Solution Approach 1:
The patent applies preliminary action by forming the first crossover before the electrons reach the object. This pre-positioned crossover creates a focused beam that maintains distinct trajectories for primary and secondary electrons even at low energies. The magnetic field configuration is established in advance to ensure proper electron path separation occurs before detection.
Solution Approach 2:
The patent introduces magnetic fields as an intermediary mechanism to separate electron trajectories. The objective lens with its magnetic unit acts as a mediator that differentiates between primary and secondary electrons based on their energy and origin, enabling detection even when their paths would otherwise overlap at low beam energies.
3Measurement precision
If the objective lens is strongly excited to create multiple crossovers, then the electron trajectory separation is improved, but the device complexity increases
Solution Approach 1:
The patent utilizes parameter changes by varying the excitation strength of the objective lens magnetic field. By adjusting the magnetic field parameters, the system creates the required multiple crossovers (first crossover before the object, second crossover at the object surface). This parameter adjustment enables trajectory separation without requiring additional hardware components.
4Productivity
If a detector is placed in the electron column to detect secondary electrons, then the detection capability is improved, but the working distance is limited due to interference with the primary electron beam
Solution Approach 1:
The patent ensures continuity of useful action by maintaining the primary electron beam path through the first crossover region while enabling simultaneous secondary electron detection. The magnetic field configuration allows both detection functions to occur continuously without interrupting either the primary beam or the secondary electron collection, effectively extending the usable working distance.
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 approach enables good image resolution and detection of secondary electrons at low energies, eliminating the detection hole issue and allowing for examinations at various working distances, including small and large distances, and is compatible with different beam generators.
Implementation Method 1
the magnetic unit is constructed and excited such that it generates at least two crossovers in series one after the other in the propagation direction of the primary particle beam
Implementation Method 2
Secondary electrons, which owing to the impingement of electrons of the primary electron beam are emitted by the object with an energy of less than 100 eV, are deflected into the electron column due to the acceleration voltage used for the primary electron beam and the field pattern or due to an existing magnetic field
Data Source
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AI summary
The invention relates to a particle beam device (1) and to a method for operating the particle beam device (1), in particular an electron beam device, having a beam generator (2) for generating a primary particle beam, having an objective lens (8) for focusing the primary particle beam onto an object (15), and having a detector (17) for detecting particles emitted by the object (15). The objective lens (8) has at least one magnetic unit (11, 12), with the magnetic unit (11, 12) generating at least one first crossover (C1, C1') and at least one second crossover (C2). The first crossover (C1, C1') is arranged in the objective lens (8) or in a region between the objective lens (8) and the object (15). The second crossover (C2) is arranged at the object (15). The invention permits the examination of the object (15) using particles which have a low energy, with good imaging properties.