Alignment Mark Height Measurement for Low-Scattering E-Beam Writing
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Solution Overview
Problem
Existing methods struggle to accurately detect alignment marks with small pattern linewidths and uneven structures formed of the same material, leading to poor signal-to-noise ratios and resist scattering during electron beam irradiation.
Innovation Solution
A position measurement apparatus using a sensor with obliquely incident laser light and a light receiver to measure the height information of a target object's surface, calculating the mark position based on the height position distribution, followed by electron beam irradiation for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the exposure intensity of the electron beam is increased to obtain contrast, then the signal-to-noise ratio is improved, but the resist scatters and contaminates the inside of the chamber
Solution Approach 1:
The patent introduces laser light as an intermediary substance to detect the alignment mark position. The laser light reflects off the mark's uneven structure, providing detection capability without requiring high-energy electron beam exposure. This mediator enables measurement while avoiding the harmful effects of high-intensity electron beam irradiation on the resist.
Solution Approach 2:
The patent replaces the electron beam-based detection system with an optical system using laser light. Instead of using charged particles to detect the mark position, the system uses photons that do not cause resist scattering or contamination, thereby substituting a harmful mechanical/physical process with a benign optical process.
2Manufacturing precision
If the pattern linewidth of the alignment mark is reduced to improve writing performance, then the manufacturing precision is improved, but the electron yield becomes small making it difficult to obtain contrast
Solution Approach 1:
The patent changes the detection parameter from electron yield to optical reflectance. Instead of relying on electron emission properties that diminish with smaller linewidths, the system measures the reflectance of laser light from the mark's uneven structure. This parameter change enables detection of sub-micron marks that would be invisible to electron beam-based contrast methods.
3Ease of manufacture
If the alignment mark is formed with an uneven structure of the same material, then the manufacturing process is simplified, but the reflectance does not change making it difficult to detect
Solution Approach 1:
The patent transitions from detecting material composition differences to detecting surface height differences. By measuring the vertical dimension (height) of the uneven structure through optical reflection angles, the system can detect marks made of uniform material. The detection dimension changes from horizontal (material type) to vertical (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
Enables accurate detection of alignment marks with small linewidths and uneven structures by reducing resist scattering and improving signal-to-noise ratio, facilitating precise positioning for electron beam writing.
Implementation Method 1
a sensor having a light projector for making laser light obliquely incident on a surface of the target object and a light receiver for receiving reflected light from the target object
Data Source
AI summary
According to one aspect of the present invention, a position measurement apparatus, includes a movable stage, a target object having an uneven mark with a concave surface and a convex surface formed of a same material being placed on the stage; and a position calculation circuit configured to calculate a position of the uneven mark using a height position distribution of the surface of the target object as the height information of the surface of the target object, the height position distribution of the surface of the target object being obtained by performing a scan with the laser light so as to cross the uneven mark and generated by a relative positional relationship between the predetermined light intensity distribution and the uneven mark.