Scattered Light Separation for Transparent Substrate Inspection
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Solution Overview
Problem
Conventional scatterometers struggle to detect defects on the polished upper surface of transparent substrates like silicon carbide and sapphire due to overwhelming scatter signals from the unpolished bottom surface.
Innovation Solution
An apparatus that separates top scattered light from bottom scattered light using a light source, objective with pinhole field stop, and sensor configuration, allowing the sensor to analyze the top surface signals without interference from the bottom surface signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional scatterometer is used to inspect the transparent substrate, then the laser beam can penetrate the substrate and reach the bottom surface, but the scatter signal from the unpolished bottom surface overwhelms the signal from defects on the top surface
Solution Approach 1:
The optical path is segmented into two distinct channels: a first optical channel for collecting scattered light from the top surface and a second optical channel for collecting scattered light from the bottom surface. This spatial segmentation allows independent detection of signals from each surface, preventing the stronger bottom surface signal from overwhelming the weaker top surface defect signals.
Solution Approach 2:
A beam splitter acts as an intermediary optical element that divides the collected scattered light into separate paths. The beam splitter enables the system to simultaneously capture signals from both top and bottom surfaces while directing them to separate detectors, thus isolating the harmful bottom surface scatter signal from the useful top surface defect signal.
2Measurement precision
If the substrate is transparent and polished on only one side, then the top surface can be inspected, but the unpolished bottom surface creates overwhelming scatter signals that mask top surface defects
Solution Approach 1:
The detection system is segmented into two independent detection channels with separate objectives and detectors. The first objective collects scattered light from the top surface while the second objective collects scattered light from the bottom surface. This segmentation enables precise measurement of top surface defects without interference from bottom surface scatter, directly addressing the signal separation difficulty.
Solution Approach 2:
The problem is solved by adding an optical dimension - using a beam splitter to create separate optical paths in different spatial directions. Instead of trying to separate signals temporally or spectrally, the system uses spatial dimensionality to direct top and bottom surface scattered light along different optical paths to separate detectors.
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 effective detection of defects on the polished top surface of transparent substrates by isolating the top scattered light from the bottom scattered light, improving defect detection accuracy.
Implementation Method 1
The beam of light thereby, (a) specularly reflects off of the top surface of the substrate to produce a specular beam
Implementation Method 2
The beam of light thereby, (c) refracts into the substrate and scatters up off of a bottom surface of the substrate to produce bottom scattered light
Implementation Method 3
scatters up off of the focal position on the top surface of the substrate to produce the top scattered light
Implementation Method 4
The objective has a first focal point focused on the focal position on the top surface of the substrate, and a second focal point focused on a pinhole field stop
Data Source
AI summary
An apparatus for detecting top scattered light from a substrate. A source directs a light onto a position on the substrate. The light thereby reflects off in a specular beam, scatters off the top surface, and scatters off a bottom surface of the substrate. An objective receives the top and bottom scattered light. The objective has a first focal point focused on the position on the top surface of the substrate, and a second focal point focused on a pinhole field stop. The pinhole field stop passes the top scattered light that is focused on the pinhole field stop, and blocks the bottom scattered light. A sensor receives and quantifies the top scattered light.