Multi-Beam Electron Optics for Stable Focus and Beam Position
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Solution Overview
Problem
Existing multi-beam electron beam writing apparatuses face challenges in maintaining writing accuracy due to rotation and magnification changes during dynamic focus, and resist charging leading to positional inaccuracies, especially when forming finer patterns.
Innovation Solution
A multi charged particle beam writing apparatus with a configuration that includes two or more-stage objective lenses, three or more correction lenses, and an electric field control electrode generating a constant electric field to lift secondary electrons, ensuring accurate beam positioning and resist charge management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dynamic focus correction is performed using electrostatic lenses during electron beam writing, then focus accuracy on irregular sample surfaces is improved, but rotation and magnification change occur in the beam array image causing writing positional accuracy to deteriorate
Solution Approach 1:
The patent divides the focus correction function into multiple independent electrostatic lenses (first, second, and third electrostatic lenses) positioned at different locations in the optical path. Each lens can be independently controlled to correct focus at different planes, allowing focus correction without significant rotation or magnification change in the beam array image.
Solution Approach 2:
The patent introduces an intermediary electrostatic lens system between the objective lens and the sample. This intermediary system performs focus correction by adjusting the electrostatic potential in a controlled manner, mediating between the need for focus correction and the need to maintain beam array image stability.
2Manufacturing precision
If an electrostatic lens is operated in a positive voltage range to generate a lifting electric field for secondary electrons, then the amount of charge on the resist surface is reduced, but the voltage changes corresponding to sample surface height causing the lifting electric field to be non-constant and preventing improvement of beam irradiation position accuracy across the entire writing region
Solution Approach 1:
The patent employs a dynamic control strategy where the voltage applied to the electrostatic lens is adjusted in real-time based on the detected sample surface height. This dynamic adjustment compensates for surface irregularities while maintaining a substantially constant lifting electric field strength across the entire writing region, ensuring consistent secondary electron suppression.
Solution Approach 2:
The patent implements a feedback control mechanism where the sample surface height is continuously detected and used to adjust the electrostatic lens voltage. This feedback loop ensures that the lifting electric field remains constant despite variations in sample surface topography, maintaining beam irradiation position accuracy throughout the writing process.
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 maintains a constant electric field to improve writing accuracy by reducing resist charging and minimizing positional deviations, enhancing the precision of pattern formation on semiconductor devices.
Implementation Method 1
an electric field control electrode to which a positive constant voltage with respect to the substrate is applied, the electric field control electrode generating an electric field between the substrate and the electric field control electrode
Implementation Method 2
two or more-stage objective lenses each comprised of a magnetic lens, and configured to focus the multi charged particle beam on a substrate
Implementation Method 3
three or more correction lenses correcting an imaging state of the multi charged particle beam on the substrate
Data Source
AI summary
In one embodiment, a multi charged particle beam writing apparatus includes two or more-stage objective lenses each comprised of a magnetic lens, and configured to focus the multi charged particle beam on a substrate, which has passed through the limiting aperture member, three or more correction lenses correcting an imaging state of the multi charged particle beam on the substrate, and an electric field control electrode to which a positive constant voltage with respect to the substrate is applied, the electric field control electrode generating an electric field between the substrate and the electric field control electrode. The two or more-stage objective lenses include a first objective lens, and a second objective lens placed most downstream in a travel direction of the multi charged particle beam. The three or more correction lenses are placed upstream of a lens magnetic field of the second objective lens in the travel direction of the multi charged particle beam.