Multi-Beam Focus Correction With Fixed Virtual Crossover
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing multi-beam writing apparatuses face issues with beam blur and defocus due to changes in sample surface height and beam current, which affect beam array distribution and perpendicular incidence, especially when using electromagnetic lenses with magnetic fields.
Innovation Solution
A multi-charged particle beam irradiation apparatus with an optical system that forms a virtual crossover in the anterior focal plane of the objective lens, using non-rotating focus correcting lenses to maintain perpendicular incidence and adjust focus based on sample surface height and beam current, ensuring the virtual crossover remains unchanged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the half-angle of beam convergence is increased to increase beam current, then beam current increases, but beam blur increases when sample surface height changes
Solution Approach 1:
The optical system is divided into multiple independent lenses (first lens, second lens, third lens) with distinct functions. The first lens forms the virtual crossover, the second lens controls beam convergence angle, and the third lens corrects focus. This segmentation allows each lens to be optimized for its specific function without compromising overall system performance.
Solution Approach 2:
A virtual crossover is introduced as an intermediary element in the optical path, formed by the first lens in its focal plane. This virtual crossover serves as a stable reference point that decouples the relationship between beam convergence angle and sample surface height, allowing the beam array distribution to remain unchanged even when focus is adjusted.
2Manufacturing precision
If focus correction is performed by changing objective lens excitation, then beam blur is suppressed, but beam array distribution changes
Solution Approach 1:
The focusing function is segmented from the objective lens to a dedicated third lens (focus correcting lens). This allows the objective lens (second lens) to maintain fixed excitation and stable beam array distribution, while the third lens handles all focus correction needs independently.
Solution Approach 2:
The virtual crossover formed by the first lens acts as an intermediary that provides a stable reference for focus correction. By adjusting the third lens while keeping the virtual crossover position fixed, focus can be corrected without altering the beam array distribution that is defined by the objective lens.
3Productivity
If beam current changes, then throughput improves, but defocus occurs due to Coulomb effect
Solution Approach 1:
The system incorporates feedback control where the third lens (focus correcting lens) dynamically adjusts focus based on the actual beam current. When beam current increases causing Coulomb defocus, the third lens excitation is adjusted to compensate, maintaining precise focus across varying throughput conditions.
4Ease of operation
If electromagnetic lens with magnetic field is used, then beam control is improved, but rotation direction deviation occurs
Solution Approach 1:
The virtual crossover serves as a stable intermediary reference that is insensitive to magnetic field rotation effects. By defining the beam array distribution relative to this virtual crossover rather than directly to the sample surface, rotation deviations caused by magnetic fields are compensated, maintaining perpendicular incidence.
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 apparatus effectively maintains beam array distribution and perpendicular incidence, correcting focus without altering beam array distribution, even with changes in sample surface height or beam current, thereby improving writing precision and throughput.
Implementation Method 1
an optical system including a plurality of lenses adjusts multiple beams emitted from a charged particle source such that a virtual crossover as viewed from a downstream side of the multiple beams is formed in an anterior focal plane of an objective lens
Implementation Method 2
the plurality of lenses include three or more focus correcting lenses configured to perform focus correction of the multiple beams in accordance with a height of a sample surface and/or beam current
Implementation Method 3
When the objective lens is an electromagnetic lens and a magnetic field is present on the sample surface
Implementation Method 4
each beam not blocked by a stopping plate is reduced by an optical system, and deflected by a deflector, then applied to a desired position on a sample
Data Source
AI summary
In one embodiment, a multi charged particle beam irradiation apparatus includes an optical system including three or more focus correcting lenses configured to adjust multiple beams, and a lens control circuit. A virtual crossover as viewed from a downstream side of the multiple beams is formed in an anterior focal plane of a lowermost objective lens. The multiple beams are perpendicularly incident on the sample surface. An actual crossover (CO2r) is located between a principal surface of an uppermost focus correcting lens and a principal surface of a lowermost focus correcting lens. The lens control circuit is configured to control a voltage applied to or a current passed through each of the focus correcting lenses such that a predetermined rotation angle condition, a condition under which a virtual crossover (CO2) as viewed from the downstream side is unchanged, and an in-focus condition are satisfied.