Electromagnetic Compound Objective Lens for LVSEM Aberration Control
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Solution Overview
Problem
Current LVSEM systems face challenges in achieving high spatial resolution and high throughput while minimizing radiation damage and aberration coefficients, particularly due to limitations in probe spot size and coil excitation, which lead to increased complexity and instability.
Innovation Solution
An electromagnetic compound objective lens is designed with a magnetic immersion lens and an electrostatic immersion lens, where the inner and outer pole pieces form a radial magnetic circuit gap, and a four-electrode electrostatic lens configuration is used to provide a retarding field, reducing aberrations and coil excitation, and enhancing the magnetic field strength near the specimen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the probe spot size is reduced to achieve high spatial resolution, then the aberration coefficients must be reduced, but this requires larger coil excitation which increases device complexity and heat conduction issues
Solution Approach 1:
A magnetic specimen stage is introduced as an intermediary component between the specimen and the magnetic objective lens. This stage carries the specimen through the magnetic field, enabling the magnetic field to extend closer to the specimen surface without requiring increased coil excitation. The magnetic stage acts as a mediator that enhances magnetic field strength at the specimen while avoiding the need for larger coils, thus resolving the contradiction between spatial resolution and device complexity
Solution Approach 2:
The invention moves the magnetic field interaction from a fixed objective lens configuration to a dynamic configuration where the specimen is moved through the magnetic field along the optical axis. This dimensional change allows the magnetic field to be applied more effectively at the specimen location without increasing coil size or excitation requirements, thereby improving spatial resolution without increasing device complexity
2Manufacturing precision
If the magnetic field strength is increased to reduce aberration coefficients, then the probe spot size decreases, but this increases heat conduction and cooling issues
Solution Approach 1:
The magnetic specimen stage serves as an intermediary that concentrates and directs the magnetic field strength precisely where needed at the specimen location. By using the magnetic stage to carry the specimen through the field, the system achieves high magnetic field strength for reduced aberrations without requiring proportionally larger coils that would generate excessive heat, thus resolving the contradiction between manufacturing precision and temperature control
Solution Approach 2:
The invention creates a localized region of high magnetic field strength at the specimen location through the magnetic stage, rather than uniformly increasing the magnetic field throughout the entire optical path. This local quality enhancement allows aberration coefficients to be reduced without proportionally increasing the overall magnetic field energy and associated heat generation, resolving the contradiction between precision and temperature
3Measurement precision
If the coil excitation is increased to reduce probe spot size, then the spatial resolution improves, but the system stability decreases due to heat conduction issues
Solution Approach 1:
The magnetic specimen stage is introduced as an intermediary that enables the system to achieve high spatial resolution without increasing coil excitation. By carrying the specimen through the magnetic field, the stage allows effective magnetic field utilization with moderate coil excitation, avoiding the heat conduction issues that would compromise system stability, thus resolving the contradiction between measurement precision and reliability
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 design achieves a higher spatial resolution with increased probe current, reducing aberration coefficients by 10-20% and minimizing radiation damage, thereby improving defect inspection and review efficiency in semiconductor yield management.
Implementation Method 1
a magnetic immersion lens including an inner pole piece and an outer pole piece, and an electrostatic immersion lens for electrically screening the magnetic immersion lens from the specimen and providing a retarding field to the primary beam, wherein the inner pole piece and the outer pole piece form a radial magnetic circuit gap facing to the examined surface of a specimen
Implementation Method 2
an electrostatic immersion lens for electrically screening the magnetic immersion lens from the specimen and providing a retarding field to the primary beam
Implementation Method 3
the electromagnetic compound objective lens is designed to have lower aberrations and low coil excitation. So, this invention can provide a higher spatial resolution with a probe current larger than before
Data Source
AI summary
An electromagnetic compound objective lens is provided for charged particle device, especially as an objective lens of low-voltage scanning electron microscope (LVSEM), which comprises a magnetic immersion lens and an electrostatic immersion lens. The magnetic immersion lens orients its gap between an inner pole piece and an outer pole piece to specimen's surface, and uses a magnetic specimen stage. The electrostatic immersion lens comprises three or four electrodes which apply suitable retarding field to a primary beam of the charged particle device for reducing its landing energy on specimen surface and further eliminating imaging aberrations.