Annular Permanent Magnet Magnetic Field Generation for Multi-Column Electron Beam Exposure
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Solution Overview
Problem
Multi-column electron beam exposure apparatuses face limitations in generating strong magnetic fields in small spaces, restricting the size of character projection masks and the pitch of column cells, which can lead to increased heat generation and coil breakdown due to reduced coil sizes.
Innovation Solution
A magnetic field generation device using two annular permanent magnets with the same polarity oriented in a direction perpendicular to their radial direction, surrounded by a ferromagnetic frame, and an electromagnetic coil placed between the magnets to adjust the magnetic field strength, allowing for the use of high-strength neodymium magnets to reduce column cell intervals and improve throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional electromagnetic coils are used to generate magnetic fields, then the magnetic field strength can be adjusted, but the coil size must be large which increases the interval between column cells and reduces throughput
Solution Approach 1:
The patent replaces the conventional electromagnetic coil system with a permanent magnet system. Specifically, it uses annular permanent magnets with radially oriented magnetization to generate the magnetic field, eliminating the need for large electromagnetic coils. This substitution dramatically reduces the required space for magnetic field generation, allowing column cells to be placed closer together (intervals of 25 mm or less), thereby increasing the number of columns that can be arranged within a given area and improving throughput.
Solution Approach 2:
The patent changes the fundamental parameter of magnetic field generation from electromagnetic induction (requiring large coils) to permanent magnetism. By using annular permanent magnets with specific magnetization directions (radial orientation), the system achieves strong magnetic fields in a compact configuration. The invention also introduces a correction coil that operates with much smaller dimensions than conventional coils, further reducing the overall footprint while maintaining field adjustability.
2Productivity
If the coil size is reduced to decrease column cell intervals, then throughput improves, but heat generation increases and coil breakdown occurs
Solution Approach 1:
The patent eliminates the problematic electromagnetic coils entirely by substituting them with permanent magnets. The annular permanent magnets generate the magnetic field without requiring electrical current, thereby completely avoiding heat generation and the associated reliability issues. The system uses only a small correction coil for fine-tuning the magnetic field, which operates under minimal thermal stress.
Solution Approach 2:
While not directly applicable to the coil replacement, this principle relates to using simpler, more robust components (permanent magnets) that have no moving parts and do not degrade from thermal cycling, effectively creating a maintenance-free magnetic field generation system.
3Productivity
If multiple column cells are arranged closely to increase throughput, then productivity improves, but magnetic field interference between adjacent cells increases
Solution Approach 1:
The patent employs annular permanent magnets with magnetization directed radially outward (or inward) from the center of each annulus. This localized magnetization pattern creates a magnetic field that is strongly concentrated within each column cell's aperture region. The radial orientation ensures that magnetic field lines are primarily confined to the vertical axis passing through each column, minimizing lateral magnetic field components that would cause interference with adjacent columns. This local field confinement enables close spacing of column cells without magnetic interference.
Solution Approach 2:
The magnetic field generation is segmented into independent annular permanent magnets for each column cell. Each annular magnet is magnetized independently with radial orientation, creating discrete, non-interfering magnetic fields. The ferromagnetic frame further segments and confines the magnetic flux to each column's region, preventing field leakage into adjacent columns.
4Manufacturing precision
If the character projection mask size is increased to improve exposure accuracy, then manufacturing precision improves, but the mask cannot be manufactured with conventional methods
Solution Approach 1:
The patent replaces the conventional large electromagnetic lens system with compact annular permanent magnets. This substitution reduces the overall optical system size, enabling the use of smaller, more manageable mask sizes (150 mm or less in diameter) that can be manufactured with conventional techniques while maintaining sufficient exposure accuracy through the efficient magnetic field generation of the permanent magnets.
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 configuration enables the reduction of column cell intervals to 25 mm or smaller, allowing more cells within a smaller area, enhancing throughput while maintaining exposure accuracy by preventing magnetic field interference between adjacent cells.
Implementation Method 1
two annular permanent magnets magnetized in a direction perpendicular to a radial direction thereof
Implementation Method 2
a ferromagnetic frame surrounding the annular permanent magnets and the electromagnetic coil
Implementation Method 3
an electromagnetic coil disposed near the annular permanent magnets and used to adjust a magnetic field of the annular permanent magnets
Data Source
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AI summary
A multi-column electron beam exposure apparatus includes: multiple column cells; an electron beam converging unit in which two annular permanent magnets and electromagnetic coils are surrounded by a ferromagnetic frame, each of the two annular permanent magnets being magnetized in an optical axis direction and being symmetrical about the optical axis, the electromagnetic coils disposed near the annular permanent magnets and used to adjust magnetic fields of the annular permanent magnets; and a substrate provided with circular apertures through which electron beams used in the column cells pass, respectively, the substrate having the electron beam converging unit disposed in a side portion of each of the circular apertures. The two annular permanent magnets may be disposed one above the other in the optical axis direction with same polarities facing each other, and the electromagnetic coils may be provided inside or outside the annular permanent magnets in their radial direction.