Transparent Specimen Height Measurement Using Separated Slit Reflections
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Solution Overview
Problem
In electron beam lithography, accurately measuring the height of a transparent material's top surface is challenging due to the inability to distinguish between slit images reflected from the top and back surfaces, leading to inaccurate height determination.
Innovation Solution
A height measuring device that uses an oblique light source and a slit member to form a slit image on the top surface, detected by an imaging element, allowing identification and separation of the slit image from the top surface from the back surface, enabling accurate measurement through image processing and binarization techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light source and slit are used to measure the height of a transparent material, then the measurement can be performed, but the slit images reflected from the top and back surfaces cannot be distinguished, leading to inaccurate height determination
Solution Approach 1:
The patent applies local quality by making the illumination non-uniform across the slit. Specifically, the illumination intensity is designed to be higher at the edges and lower at the center of the slit. This creates a characteristic illumination pattern that, when reflected, allows differentiation between top surface and back surface reflections based on their respective illumination characteristics. The top surface reflection retains the original illumination pattern while the back surface reflection undergoes additional optical path effects, enabling distinction between the two.
Solution Approach 2:
The patent introduces a new dimension for differentiation by using the illumination intensity distribution across the slit width as the distinguishing feature. Instead of relying on position alone, the method utilizes the intensity profile across the slit image, creating a two-dimensional characterization (position + intensity distribution) that enables separation of top and back surface reflections that would otherwise be indistinguishable in a one-dimensional position-based measurement.
2Device complexity
If the slit image position is used to determine height, then the measurement process is simple, but the height determination becomes inaccurate when multiple slit images are present
Solution Approach 1:
The patent changes the illumination parameter from uniform to non-uniform (edge-enhanced) intensity distribution. This parameter change transforms the reflected light pattern in a way that encodes surface identification information within the intensity profile itself. The measurement process remains relatively simple, but the changed illumination parameter enables accurate differentiation between top and back surface reflections, resolving the contradiction between simplicity and accuracy.
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 precise measurement of the top surface height by distinguishing between slit images from the top and back surfaces, preventing misinterpretation and ensuring accurate data for subsequent lithography processes.
Implementation Method 1
a slit image of reflected light reflected by a top surface of a specimen and a slit image of reflected light reflected by a back surface of the specimen are detected
Data Source
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AI summary
A height measuring device (200) includes a light source (210) that emits light in a direction oblique to a top surface of a specimen (2), a slit (108) that shapes the light from the light source (210) to form a slit image on the specimen (2), an imaging element (230) that detects reflected light reflected by the specimen (2), and an arithmetic unit (240) that determines a height of the top surface of the specimen (2) based on a result of detection of the slit image by the imaging element (230). The arithmetic unit (240) performs processing of: identifying, when a plurality of slit images are detected by the imaging element (23), a slit image of the reflected light reflected by the top surface of the specimen (2) from among the plurality of slit images based on respective positions of the plurality of slit images on a detection surface (232) of the imaging element (230); and determining the height of the top surface of the specimen (2) based on the position of the slit image of the reflected light reflected by the top surface of the specimen (2) on the detection surface (232).