Multibeam Focus Adjustment via Beam Thinning for Lithography
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Solution Overview
Problem
In charged-particle-beam lithography apparatuses with a multibeam system, focus adjustment is challenging when beam lines are inclined relative to the end edge of a mark, as overlap between adjacent beam lines during scanning leads to rounded signal waveforms that cannot be distinguished from defocusing, making appropriate focus adjustment difficult.
Innovation Solution
A method that involves acquiring the rotation angle of beam lines with respect to the mark, determining selection beams by thinning beam lines based on the rotation angle using a formula, and adjusting the focus based on reflected electrons scanned orthogonally to the mark's end edge, ensuring accurate focus adjustment by suppressing waveform rounding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If beam lines are inclined relative to the end edge of the mark during scanning, then the multibeam system can cover a wider area, but overlap between adjacent beam lines occurs causing waveform rounding that prevents accurate focus adjustment
Solution Approach 1:
The patent segments the beam lines by selectively turning off specific beams based on their position and the rotation angle. This segmentation prevents overlap between adjacent beam lines during scanning, eliminating the waveform rounding problem while maintaining the ability to cover the required scan area through the coordinated operation of remaining beams
Solution Approach 2:
The patent performs preliminary determination of the rotation angle before scanning begins, and pre-calculates which beams should be turned off based on this angle. This preliminary action allows the system to configure the beam selection in advance, ensuring that no overlap occurs during the actual scanning process and enabling accurate focus adjustment
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 method allows for appropriate focus adjustment of multibeams even when beam lines are rotated, preventing overlap-induced waveform rounding and enabling precise focus setting by determining the optimal excitation amounts for the objective lens.
Implementation Method 1
an excitation amount at a time when the rising of the waveform of the signal becomes sharpest is set to the objective lens as a focus during drawing
Implementation Method 2
acquire a signal of reflected electrons while excitation amounts of an objective lens are allocated
Data Source
AI summary
A multibeam-focus adjusting method in a charged-particle-beam lithography apparatus that draws a pattern by irradiating a sample with multibeams having a plurality of beam lines through a plurality of lines of opening portions provided on an aperture member, the method adjusting a focus of the multibeams and including: acquiring a rotation angle of the beam lines with respect to an end edge of a mark provided at a predetermined position; determining selection beams to be used for adjustment among the multibeams based on the acquired rotation angle; and adjusting a focus of the multibeams based on reflected electrons acquired by irradiating the mark with the selection beams and scanning the mark in a direction orthogonal to the end edge of the mark.