Multi-axis Magnetic Immersion Objective Lens with Radial Gaps
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Solution Overview
Problem
Multi-axis magnetic lenses used in semiconductor defect inspection face issues with non-axisymmetric transverse field components causing beam deflection and aberrations, and variations in magnetic field strength between sub-lenses leading to uneven focusing and reduced spatial resolution and throughput.
Innovation Solution
A multi-axis magnetic immersion objective lens with radial magnetic circuit gaps and a magnetic specimen stage to reduce coil excitation and aberrations, combined with a multi-axis electrostatic immersion objective lens for deceleration and a deflection scanning and compensation unit to correct residual field effects, forming a multi-axis electromagnetic compound immersion objective lens for improved focusing and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multi-axis magnetic lens is used to focus multiple parallel electron beams, then throughput is improved, but non-axisymmetric transverse field components cause beam deflection and aberrations
Solution Approach 1:
A magnetic shielding plate with through holes is introduced as an intermediary component between the magnetic conductor plates and the electron beams. This shielding plate creates symmetric magnetic circuits through its magnetic paths, effectively canceling non-axisymmetric transverse field components while preserving the multi-axis focusing capability for high throughput inspection
Solution Approach 2:
The invention intentionally introduces asymmetric magnetic shielding structures that create symmetric magnetic flux distribution. By strategically placing magnetic shielding plates with specific through-hole patterns, the system transforms the inherently asymmetric multi-axis magnetic field into a symmetric configuration that eliminates beam deflection and aberrations
2Manufacturing precision
If the magnetic field strength is increased to improve focusing, then spatial resolution is improved, but coil excitation and thermal issues increase
Solution Approach 1:
Magnetic shielding plates serve as intermediaries that concentrate and guide magnetic flux through defined paths. This allows achieving strong focusing effects at the specimen plane without proportionally increasing coil excitation, as the shielding plates efficiently channel the magnetic field where needed while reducing overall system thermal load
Solution Approach 2:
The invention changes the magnetic circuit configuration by introducing shielding plates with specific geometries and materials. This modifies the magnetic field distribution parameters, allowing high field strength at the focal plane with reduced total magnetic flux requirements, thereby lowering coil excitation and thermal generation
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 solution provides higher spatial resolution and higher throughput in semiconductor defect inspection by minimizing aberrations and radiation damage, enabling effective inspection of semiconductor wafers and masks with improved magnetic field immersion and reduced thermal issues.
Implementation Method 1
a plurality of magnetic sub-lenses (300-M1 to 300-Mn) with radial magnetic circuit gaps (G3) facing the specimen surface (60)
Implementation Method 2
a plurality of electrostatic sub-lenses (300-E1 to 300-En) overlapping with the magnetic sub-lenses
Implementation Method 3
The magnetic specimen stage enhances the magnetic field of each sub-lens and moves its peak closer to the specimen
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
Multi-axis magnetic immersion objective lens, with a pair of magnetic pole plates 51,50 with aligned apertures and with a common coil 44 surrounding the pole plates. Each aperture in both plates contains a magnetic insert ring 311,312 , spaced from the respective aperture wall by a radial gap G1,G2 (formed by vacuum or a non-magnetic material), and each upper magnetic ring 311 extends downward through inside the corresponding lower magnetic ring 312 with a second radial gap G3.