Objective Lens Displacement for Charged Particle Focusing
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Solution Overview
Problem
Conventional particle-optical systems face challenges in achieving high resolution and precise focusing of charged particles at small working distances due to the fixed alignment of magnetic and electrostatic lenses, which leads to image shift and chromatic errors.
Innovation Solution
An objective lens design that includes a magnetic lens with an inner and outer pole piece and an electrostatic lens with adjustable electrode arrangements, allowing for precise displacement of the lenses relative to each other using actuators, ensuring accurate alignment of optical axes and improved field overlap for enhanced focusing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic and electrostatic lenses are fixed in alignment, then the system structure is simple, but image shift and chromatic errors occur at small working distances
Solution Approach 1:
The patent makes the electrostatic lens displaceable relative to the magnetic lens along the optical axis using an actuator mechanism. This dynamic adjustment capability allows the system to optimize the overlap between electrostatic and magnetic fields for different working distances, eliminating image shift and chromatic errors while maintaining manageable structural complexity through controlled motion rather than fixed complex alignment
Solution Approach 2:
The patent changes the positional parameter of the electrostatic lens relative to the magnetic lens to optimize field overlap. By adjusting the distance and relative position between the two lens types, the system achieves optimal imaging properties at different working distances, transforming a static alignment problem into a可调 parameter optimization problem
2Reliability
If the electrostatic lens is displaced relative to the magnetic lens, then field overlap is improved for better focusing, but the alignment adjustment mechanism becomes more complex
Solution Approach 1:
The patent segments the lens system into independently adjustable components: the magnetic lens remains fixed while the electrostatic lens is mounted on a separate movable platform with its own actuator. This segmentation allows precise control of the electrostatic lens position to optimize field overlap without requiring complex integrated alignment mechanisms for the entire system
Solution Approach 2:
The patent replaces complex mechanical alignment mechanisms with a controlled actuator system that provides precise, repeatable positioning of the electrostatic lens. This substitution uses automated actuation (likely piezoelectric or motor-driven) to achieve and maintain optimal field overlap, reducing the need for manual mechanical adjustment while improving focusing accuracy
3Measurement precision
If working distance is reduced for better inspection resolution, then imaging detail is improved, but chromatic errors and image shift increase
Solution Approach 1:
The patent employs dynamic adjustment of the electrostatic lens position that can be optimized for different working distances. When operating at reduced working distances for better inspection resolution, the actuator adjusts the electrostatic lens to achieve optimal field overlap with the magnetic lens, thereby minimizing chromatic errors and image shift that would otherwise increase at small working distances
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 enables improved imaging properties, reduced error coefficients, and higher resolution, especially at small working distances, by allowing for precise adjustment and alignment of the magnetic and electrostatic fields, minimizing image shift and chromatic errors.
Implementation Method 1
a magnetic lens which has an inner pole piece and an outer pole piece. A gap is formed between a lower end of the inner pole piece and an inner end of the outer pole piece
Implementation Method 2
The magnetic lens and the electrostatic lens are adapted to be displaceable relative to each other
Implementation Method 3
The electrostatic lens has an electrode arrangement for generating an electrostatic field. The electrode arrangement includes a first electrode and a second electrode offset from each other in a direction traverse to the charged particles
Implementation Method 4
an actuator for changing a position of the first electrode and the second electrode of the electrostatic lens relative to a position of the magnetic lens
Data Source
AI summary
An objective lens for focussing charged particles includes a magnetic lens and an electrostatic lens whose components are displaceable relative to each other. The bore of the outer pole piece of the magnetic lens exhibits a diameter Da which is larger than a diameter Di of the bore of the inner pole piece of the magnetic lens. The following relationship is satisfied: 1.5·Di≦Da≦3·Di. The lower end of the inner pole piece is disposed in a distance of at least 2 mm offset from the inner end of the outer pole piece in a direction of the optical axis.