Compound Objective Lens for Electron Beam Wafer Inspection
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Solution Overview
Problem
Existing electron beam wafer inspection systems face challenges with low landing energy and low secondary electron extraction fields, leading to reduced objective lens performance and increased aberrations, making it difficult to focus on large samples effectively.
Innovation Solution
An electron beam wafer imaging system with a compound objective lens having a magnetic and electrostatic component, where the electrostatic lens component includes three electrodes and a control electrode to adjust the focal length and extraction field, allowing switching between operational modes to maintain high optical performance across varying energy levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If longer focal length electrostatic lenses are used to overcome focusing problems at low landing energy, then focusing capability on large samples is improved, but lens aberrations increase
Solution Approach 1:
The patent combines magnetic and electrostatic lens components into a compound objective lens system. The magnetic lens component provides primary focusing while the electrostatic lens component fine-tunes the focal length and reduces aberrations, achieving both good focusing capability and low aberrations simultaneously
Solution Approach 2:
The electrostatic lens component's focal length is made dynamically adjustable through voltage control. By varying the voltage applied to the electrostatic lens electrodes, the system can optimize the focal length for different sample sizes and landing energies, maintaining focusing capability while minimizing aberrations
2Measurement precision
If column energy is reduced to improve focusing at low landing energy, then focusing performance is improved, but optics performance deteriorates due to smaller immersion factor
Solution Approach 1:
The compound objective lens merges magnetic and electrostatic components where the magnetic lens maintains high immersion factor for good optics performance, while the electrostatic lens provides the necessary focal length adjustment for low landing energy focusing
Solution Approach 2:
The system changes the operational parameters by applying different voltages to the electrostatic lens component while maintaining constant column energy. This allows optimization of focal length and immersion factor independently, achieving both good focusing performance and maintained optics performance
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 system achieves high optical performance at moderate landing energies while enabling low landing energy and low extraction field operation without compromising performance, allowing for improved focusing and imaging of large samples.
Implementation Method 1
an objective lens for focusing the electron beam on a wafer, wherein the objective lens has a magnetic lens component
Implementation Method 2
the electrostatic lens component has a first electrode, a second electrode and a third electrode; between which the primary beam is decelerated
Implementation Method 3
the emitter is a cold field emitter, a thermally assisted field emitter, or a Schottky emitter
Implementation Method 4
the emitter is a cold field emitter, a thermally assisted field emitter, or a Schottky emitter
Data Source
Figure 1~2B
Figure 3
Figure 4
AI summary
An electron beam wafer imaging system is described. The system includes an emitter for emitting an electron beam, wherein the emitter is a cold field emitter, a thermally assisted field emitter, or a Schottky emitter; a power supply for applying a voltage between the emitter and the column housing of at least 20 kV; an objective lens for focusing the electron beam on a wafer, wherein the objective lens has a magnetic lens component and an electrostatic lens component, wherein the magnetic lens component and the electrostatic lens component substantially overlap each other, wherein the electrostatic lens component has a first electrode, a second electrode and a third electrode; and a control electrode positioned along an optical axis from the position of the third electrode to the position of a specimen stage, wherein the control electrode is configured for control of signal electrons; a controller to switch between a first operational mode and a second operational mode, wherein the controller is connected to a further power supply for switching between the first operational mode and the second operational mode.