Swing Objective Lens for SEM Aberration Control
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Solution Overview
Problem
Conventional optical inspection tools are inadequate for identifying small defects in sub-20 nanometer semiconductor nodes, and existing e-beam inspection tools face challenges with resolution and throughput, particularly in achieving large tilting angles necessary for inspecting stereo structures.
Innovation Solution
A swing objective lens system that includes a pre-lens deflector and a swing deflector within an immersion objective lens, allowing for the tilting of a charged particle beam to a predetermined angle, which focuses the beam onto a specimen with reduced paraxial aberration and increased scanning field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical inspection tools are used, then the inspection process is simple and fast, but they cannot identify small defects in sub-20 nanometer semiconductor nodes
Solution Approach 1:
The patent replaces conventional optical inspection systems with an electron beam-based inspection system. Electrons have much shorter wavelengths than visible light, enabling resolution of sub-20 nanometer defects. The electron optical system including condenser lenses, objective lenses, and deflectors substitutes the mechanical/optical inspection apparatus while achieving superior measurement precision.
Solution Approach 2:
The patent introduces an electron beam as an intermediary between the inspection system and the specimen. The electron beam interacts with the semiconductor structure to generate signals (secondary electrons, backscattered electrons) that reveal defect information. This intermediary enables detection of nanoscale features that optical methods cannot resolve.
2Measurement precision
If e-beam inspection tools are used to achieve high resolution, then defect identification capability improves, but throughput decreases
Solution Approach 1:
The patent employs dynamic control of the electron beam through rapid scanning mechanisms and adjustable lens systems. The beam can be quickly repositioned and refocused during inspection, enabling high-speed scanning of large areas while maintaining high resolution. This dynamic operation allows the system to achieve both high measurement precision and high productivity by adapting beam parameters in real-time.
Solution Approach 2:
The patent divides the inspection process into multiple scanning passes or zones, allowing parallel processing or optimized scanning strategies for different areas. Large specimens can be inspected in segmented regions with coordinated beam movement, increasing overall throughput while maintaining resolution through consistent beam parameters across segments.
3Area of stationary object
If large tilting angles are used to inspect stereo structures, then the scanning field of view increases, but paraxial aberration increases
Solution Approach 1:
The patent employs asymmetric lens designs and asymmetric deflector configurations to compensate for aberrations introduced by large tilting angles. The optical elements are specifically shaped and positioned to counteract the asymmetric distortion that occurs when the electron beam strikes the specimen at high angles, maintaining beam focusing precision across the expanded field of view.
Solution Approach 2:
The patent dynamically adjusts electron optical parameters (lens currents, deflector voltages, beam energy) as the tilting angle changes. By continuously optimizing these parameters during inspection, the system maintains minimal paraxial aberration even when scanning large areas or inspecting three-dimensional structures at various angles.
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 solution enhances defect identification and analysis capabilities by providing high-resolution, low-aberration images with increased throughput, enabling effective inspection of nanostructures and improving semiconductor product yield.
Implementation Method 1
a pre-lens deflector above and adjacent to a magnetic lens generated by the immersion objective lens
Implementation Method 2
a swing deflector located inside said immersion objective lens and providing an electrostatic field with a first condition
Implementation Method 3
an immersion objective lens for focusing a charged particle beam on a specimen
Data Source
AI summary
A scanning electron microscope (SEM) with a swing objective lens (SOL) reduces the off-aberrations to enhance the image resolution, and extends the e-beam scanning angle. The scanning electron microscope comprises a charged particle source, an accelerating electrode, and a swing objective lens system including a pre-deflection unit, a swing deflection unit and an objective lens, all of them are rotationally symmetric with respect to an optical axis. The upper inner-face of the swing deflection unit is tilted an angle θ to the outer of the SEM and its lower inner-face is parallel to the optical axis. A distribution for a first and second focusing field of the swing objective lens is provided to limit the off-aberrations and can be performed by a single swing deflection unit. Preferably, the two focusing fields are overlapped by each other at least 80 percent.