Charged Particle Beam Writing Surface Height Correction
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Solution Overview
Problem
Existing charged particle beam writing methods face challenges in accurately focusing the electron beam on warped or deformed sample surfaces due to measurement errors caused by insufficient laser beam intensity and poor coupling between the laser interferometer and Z sensor, leading to displacement and defocus issues.
Innovation Solution
A charged particle beam writing apparatus that includes height measuring means, approximated curved surface generating means, and height correcting means to measure, generate, and correct the surface height based on reliable data, using interpolation techniques like cubic spline interpolation to create a height distribution map and adjust the electron beam focus accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If height measurement is performed using a Z sensor with laser interferometer, then the height of sample surface can be measured, but measurement errors occur due to insufficient laser beam intensity and poor coupling
Solution Approach 1:
The patent introduces an intermediary process of generating an approximated curved surface from measured height data. This intermediary representation serves as a mediator between the noisy measurement data and the final focusing operation, allowing the system to tolerate measurement errors while achieving accurate beam focusing.
Solution Approach 2:
The patent performs preliminary actions by generating an approximated curved surface model before the actual focusing operation. This preliminary model creation allows errors in individual height measurements to be corrected through the approximation process, ensuring reliable focusing even when some measurements are inaccurate.
2Ease of operation
If electron beam is continuously focused at a single height determined at a selected point, then the focusing operation is simple, but beam displacement and defocus occur due to sample surface deformation
Solution Approach 1:
The patent applies dynamics by making the focusing height variable across different spatial locations on the sample surface. Instead of a fixed single height, the system dynamically adjusts the focal plane according to the approximated curved surface model, allowing the focus to adapt to surface deformations while maintaining operational simplicity through automated control.
Solution Approach 2:
The patent implements local quality by allowing different regions of the sample surface to have different focal heights. The approximated curved surface model enables each location to be focused at its appropriate height according to the local surface topology, rather than using a uniform focus height for the entire surface.
3Loss of information
If interpolation is performed using height measurements of several points, then the height distribution map can be created, but measurement errors propagate and cause distortion in the map
Solution Approach 1:
The patent changes the parameter representation by transforming discrete height measurement points into a continuous approximated curved surface model. This parameter transformation allows the system to smooth out measurement errors while preserving the overall height distribution information, creating a more reliable representation of the sample surface topology.
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 approach enables accurate focusing of the charged particle beam on sample surfaces even with measurement errors, ensuring precise pattern writing by generating a reliable height distribution map and correcting for surface irregularities, thereby preventing beam displacement and defocus.
Implementation Method 1
a laser interferometer is disposed to face the mirror surface of the moving mirror. The laser interferometer is adapted to measure the XY coordinates of the XY stage and the angle of rotation of the XY stage in the X-Y plane by using the laser light reflected from the moving mirror.
Implementation Method 2
The detection beam emitted downward at an angle from the projector impinges on the surface of the sample and is reflected upward at an angle to enter the photodetector. The parameters of this reflected beam incident on the photodetector are measured to detect the height of the sample surface.
Data Source
AI summary
The height of selected points on the surface of a mask is measured, and if the number of measurement errors in this measurement is less than a predetermined value, an approximated curved surface for the mask surface is generated. The measurement data and height data obtained from the approximated curved surface are then compared, and if there is no point at which the difference between the measurement data and the data obtained from the approximated curved surface is greater than a predetermined threshold value, then it is determined that the reliability of the approximated curved surface is high and the height of the mask surface is corrected in accordance with this approximated curved surface.