Level Sensor Optical Path Modulation for Substrate Warpage
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Solution Overview
Problem
Existing level sensors face challenges in accurately detecting the height levels of substrates with high surface steps or warpage, leading to deterioration in detection performance and limited detection ranges in the Z direction.
Innovation Solution
A level sensor configuration that utilizes a measurement light source, a prism to split reflected light into polarized components, an optical path length modulator to maintain constant and varying optical paths, and a detector to detect the optical path length difference based on interference signals, enabling precise height level detection regardless of surface irregularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical sensing methods are used, then the detection process is simple, but the detection range in the Z direction is limited and detection performance deteriorates with high surface steps or warpage
Solution Approach 1:
The patent changes the detection parameter from simple optical intensity to optical path length difference. By using interferometry to measure the phase difference between reference and measurement light, the system achieves high precision detection across extended Z-direction ranges, resolving the contradiction between detection performance and detection range.
Solution Approach 2:
The patent introduces a reference light path as an intermediary element. The reference light interferes with the measurement light to create an interference pattern that encodes height information, enabling accurate detection of surface height variations even over large Z-direction ranges without sacrificing detection performance.
2Measurement precision
If non-contact optical sensing is used, then the substrate surface is not contaminated, but detection accuracy decreases for substrates with high surface steps or warpage
Solution Approach 1:
The patent employs dynamic optical path length modulation to adapt to varying surface conditions. By modulating the optical path length and analyzing the interference signal variations, the system maintains high measurement precision across substrates with different surface characteristics, including those with high surface steps or warpage, without physical contact that could cause contamination.
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 proposed level sensor achieves high detection performance with extended range in the Z direction, ensuring reliable height level detection even with high surface steps or substrate warpage, thereby enhancing the reliability of substrate processing apparatuses.
Implementation Method 1
a prism configured to split reflected light of the measurement light, which is reflected by the substrate, into first polarized light and second polarized light and generate a first optical path length difference between the first polarized light and the second polarized light
Implementation Method 2
a photo-elastic modulator configured to keep constant an optical path length of the first polarized light and periodically change an optical path length of the second polarized light
Implementation Method 3
a detector configured to receive the first polarized light and the second polarized light, which are output from the optical path length modulator, and detect the first optical path length difference based on an interference signal generated by interference between the first polarized light and the second polarized light
Data Source
AI summary
Provided are a level sensor configured to detect a height level of a substrate, and a substrate processing apparatus including the level sensor. The level sensor includes a measurement light source configured to radiate measurement light toward the substrate, a prism configured to split reflected light of the measurement light into first polarized light and second polarized light and generate a first optical path length difference between the first polarized light and the second polarized light, an optical path length modulator configured to keep constant an optical path length of the first polarized light and periodically change an optical path length of the second polarized light, and a detector configured to detect the first optical path length difference based on an interference signal between the first polarized light and the second polarized light.