Charged Particle Beam Aperture for High-Resolution SEM Inspection
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Solution Overview
Problem
Scanning electron microscopes face challenges in achieving high image resolution and accuracy due to large working distances, which result in increased aberrations and electrostatic field leakage, reducing the system's efficiency in inspecting semiconductor wafers.
Innovation Solution
A double deflection system and a narrow aperture with a very thin portion are introduced to reduce the working distance, minimizing electrostatic field leakage and chromatic aberration, while a precise height calibration method is used to maintain accurate focusing, allowing for improved resolution and accuracy with low energy electron beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the working distance is increased to accommodate the aperture, then the system can be manufactured with standard components, but the image resolution and accuracy deteriorate due to increased aberrations and electrostatic field leakage
Solution Approach 1:
The patent introduces a vertical dimension by positioning the aperture in a plane above the sample rather than in the traditional lateral plane. This dimensional reconfiguration allows the aperture to be positioned closer to the sample (reduced working distance) without compromising the beam path, thereby improving resolution while maintaining manufacturability through standardized components.
Solution Approach 2:
The patent introduces an electrostatic lens as an intermediary element between the electron beam and the sample. This lens focuses and controls the electron beam, compensating for aberrations that would otherwise occur at reduced working distances, thereby maintaining image resolution while allowing the aperture to be positioned closer to the sample.
2Measurement precision
If the working distance is reduced to improve resolution, then chromatic aberration and electrostatic field leakage are minimized, but the system becomes more difficult to manufacture and align
Solution Approach 1:
The patent designs the aperture assembly to serve multiple functions simultaneously: it defines the beam path, positions the electrostatic lens, and maintains the required working distance geometry. This multi-functionality reduces the need for separate alignment mechanisms and simplifies the overall system construction despite the reduced working distance.
Solution Approach 2:
The patent employs the electrostatic lens to create equipotential regions that control electron beam propagation. By establishing controlled potential fields, the system compensates for the increased complexity of reduced working distance configurations, making alignment and manufacturing more manageable while maintaining high resolution.
3Measurement precision
If high acceleration voltage is used to reduce spot size, then image resolution improves, but sample damage occurs due to high energy beam
Solution Approach 1:
The patent dynamically changes the acceleration voltage parameter during operation. The electron beam is accelerated to high voltage for most of its path to achieve small spot size and high resolution, then decelerated by the electrostatic lens just before impacting the sample. This parameter change allows the system to achieve nanometer-scale resolution without causing sample damage from high-energy electron impact.
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 enhances the resolution by over 20% and improves the accuracy of the system by reducing distortions and increasing the collection efficiency of the in-lens detector, effectively addressing the limitations of existing SEMs.
Implementation Method 1
The electrostatic part of the compound magnetic-electrostatic lens is an electrostatic retarding lens (with respect to the primary charged particle beam), and has electrodes held at different potentials
Implementation Method 2
The electron beam column includes, inter alia, a beam focusing/deflecting arrangement formed by a lens assembly and a deflector assembly
Implementation Method 3
Irradiation of the sample with the primary electron beam releases secondary (and/or backscattered) electrons
Data Source
AI summary
A method and system for inspecting an inspected object. The system includes: a detector adapted to detect charged particles scattered from a sample; a magnetic lens adapted to generate a magnetic field such as to direct a charge particle beam towards a sample and an first electrode positioned very close to an inspected object, wherein the first electrode comprises a very thin portion that defines a narrow aperture through which the charged particle beam can propagate.