Substrate Surface Defect Detection Using Phase-Shifting Interferometry
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Solution Overview
Problem
Current methods for detecting surface defects on semiconducting substrates, such as slip lines, are inefficient, particularly in detecting small defects and those near the substrate's edges, and cannot analyze substrates at a rate compatible with industrial production due to high costs and long processing times.
Innovation Solution
A method involving the projection of a pattern of light fringes and dark bands onto the substrate, followed by relative displacement and image acquisition using a CCD sensor to calculate phase offsets and gradients, allowing for rapid detection of surface defects, including small slip lines, and determining their position and nature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical detection methods are used to detect slip lines on substrates, then the detection can be performed, but the method cannot detect slip lines around the edge of the substrate where the wafer has a rounded edge
Solution Approach 1:
The invention transitions from conventional 2D surface optical inspection to 3D topography mapping using phase-shifting interferometry. By measuring the optical path difference caused by surface height variations, the system can detect slip lines and other defects across the entire substrate surface including rounded edges, converting a surface inspection problem into a three-dimensional surface profiling solution.
2Measurement precision
If powerful and complex laboratory devices are used to detect all optical defects, then practically all defects can be detected, but the analysis rate is only about 7 substrates per hour which is not compatible with industrial production
Solution Approach 1:
The invention replaces complex mechanical scanning systems with a stationary phase-shifting interferometry system. By using phase-shifting algorithms and digital image processing, the system achieves high-resolution defect detection without mechanical movement, enabling rapid acquisition of surface topography data at industrial production speeds while maintaining laboratory-grade detection sensitivity.
Solution Approach 2:
The system employs periodic phase shifting of the reference wavefront to acquire multiple interferograms. By introducing known phase delays (typically 0, 90°, 180°, 270°) and processing these periodic measurements through algorithms like the four-step phase-shifting method, the system extracts precise surface height information rapidly, achieving both high precision and high speed.
3Reliability
If conventional detection methods are used, then the process can be completed, but the detection of small amplitude slip lines is not effective and requires particularly long development time
Solution Approach 1:
The system performs preliminary phase calibration and reference surface measurement before actual defect detection. By pre-establishing the phase relationship between reference and test waves and storing reference interferograms, the system eliminates the need for time-consuming adjustments during production, enabling rapid and reliable detection of small amplitude slip lines from the start.
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 fast detection of surface defects, including those at the substrate's edges, within less than 30 seconds, significantly increasing the analysis rate to over 100 substrates per hour while maintaining high resolution for small defects.
Implementation Method 1
projection of a pattern composed of an alternation of light fringes and dark bands onto the substrate, so as to generate fringes reflected by the substrate surface
Implementation Method 2
acquisition of a sequence of at least three images of the pattern reflected by the substrate by a sensor
Data Source
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AI summary
Method for detecting surface defects on a substrate and device using said method. This invention relates to a method for detecting surface defects, such as =slip line= type defects, on a substrate (2) designed to be used in electronics, optoelectronics or analogue, remarkable in that it comprises at least the following steps: -projection of a pattern composed of an alternation of light fringes and dark bands onto the substrate (2), so as to generate fringes reflected by the surface of the substrate (2), -relative displacement of the pattern and the substrate (2) along at least one direction, so as to displace the fringes of the pattern on the substrate (2), -acquisition of a sequence of at least three images of the pattern reflected by the substrate (2) by a sensor (8), the images corresponding to displacement of the fringes of the pattern, -determination of the gradient of the surface of the substrate (2) using displacements of fringes of the pattern, and -determination of the presence of a surface defect on the substrate (2) using variations in the gradient of the surface of the substrate (2). Another purpose of the invention relates to a device using said method.