Transparent Substrate Inspection for Frontside-Backside Defect Discrimination
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Solution Overview
Problem
Existing inspection systems struggle to unambiguously distinguish defects on the frontside from defects on the backside of transparent substrates due to light scattering from both sides, leading to ambiguous defect identification.
Innovation Solution
An inspection system and method that utilizes coherent light beams to create a measurement volume with interference fringes, scanning the substrate tangentially to distinguish defects on the frontside from those on the backside by identifying a specific pattern in the scattered light signal, including filtering and applying transformation functions to enhance defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dark field inspection using Laser Doppler Velocimetry is used to inspect transparent substrates, then frontside defects can be detected, but backside defects contaminate the signal making unambiguous identification impossible
Solution Approach 1:
The patent segments the inspection process into distinct temporal phases: a first inspection phase capturing frontside defects and a second inspection phase capturing backside defects. By separating the detection of defects from opposite sides into distinct time windows, the system eliminates signal contamination and enables unambiguous defect identification.
2Productivity
If the measurement spot scans across the substrate, then defects can be detected, but light scattered from backside defects contaminates the signal from frontside defects
Solution Approach 1:
The patent performs preliminary actions by conducting the frontside inspection first, recording the signal characteristics. Then it performs the backside inspection second, using the temporal separation to distinguish which defects originated from which side. This sequential approach maintains inspection coverage while ensuring reliable defect location 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
Effectively discriminates between frontside and backside defects on transparent substrates, providing clear and accurate defect characterization, enabling separate signal representation for each side.
Implementation Method 1
an optical source emitting a first and a second light beams oriented in relation to one another so as to form, at their intersection, a measurement volume comprising a plurality of parallel interference fringes
Implementation Method 2
A Doppler pulse is a signal that has a double frequency component: a low-frequency component, forming the envelope of the signal, corresponding to the mean light intensity scattered by the defect, and a high-frequency component, corresponding to the Doppler frequency containing the information on the velocity of the defect through the measurement spot
Data Source
Figure 1~2
Figure 3a~5
Figure 6a~6b
AI summary
The invention concerns a device and method for discriminating defects present on a frontside of a substrate (S) from defects present on a backside of the substrate, the substrate being made of a material transparent at an inspection wavelength. It comprises disposing the substrate in an inspection system (1) comprising at least one optical source (2) coupled to an optical system (4, 5, 7, 7') the substrate being disposed on a support (8) and being positioned with respect to the optical system such that a first and a second light beams (6, 6') intersect at a measurement spot on the frontside of the substrate, and controlling (12) the relative movement of the support and of the optical system to scan the measurement spot along a measurement path on the frontside of the substrate, the relative movement being controlled such that the reference plane is kept tangential to the measurement path. The method further comprises identifying in a signal a first pattern presenting two intensity peaks separated from each other by a determined separation interval, the first pattern corresponding to the light scattered by a particle on the backside of the substrate.