Wafer Defect Inspection Apparatus Dynamic Exposure Control
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Solution Overview
Problem
Conventional wafer defect inspection methods fail to detect defects appropriately in low resistivity silicon wafers, as the same imaging recipe applied to all wafers in a lot may result in an average gray level outside the detectable range, and require time-consuming specific resistance measurements.
Innovation Solution
A wafer defect inspection apparatus that adjusts exposure time and infrared light intensity to ensure the image gray level is within a predetermined range, using a gray level judgment mechanism and control means to modify imaging conditions dynamically, and includes a differential value calculation to identify defect candidate picture elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the same recipe is applied to all wafers in a lot, then the inspection process is simple and fast, but the average gray level of low resistivity wafers falls outside the defect detectable range
Solution Approach 1:
The system performs preliminary measurement of the average gray level of each wafer before the actual defect inspection. Based on this preliminary measurement, the exposure time is adjusted in advance to ensure the gray level falls within the defect detectable range, allowing high-speed inspection without sacrificing detection accuracy.
Solution Approach 2:
The inspection system dynamically adjusts the exposure time parameter based on the measured average gray level of each wafer. This dynamic adjustment allows the system to adapt to variations in wafer resistivity while maintaining defect detection accuracy, resolving the contradiction between fixed simple inspection and adaptive precise inspection.
2Measurement precision
If specific resistance measurement is performed for each wafer, then the gray level can be adjusted appropriately, but the inspection time and operational complexity increase significantly
Solution Approach 1:
The system extracts and measures only the essential parameter (average gray level) during the imaging process itself, rather than performing a separate specific resistance measurement. This extraction approach provides sufficient information for exposure time adjustment without adding significant time overhead, resolving the contradiction between precise gray level control and inspection speed.
Solution Approach 2:
The imaging system serves multiple functions: it captures the wafer image for defect inspection and simultaneously measures the average gray level for exposure time adjustment. This multi-functionality eliminates the need for separate specific resistance measurement equipment and procedures, reducing operational complexity while maintaining gray level control accuracy.
3Measurement precision
If exposure time is adjusted for each wafer, then the gray level falls within the detectable range, but the inspection process becomes more complex and time-consuming
Solution Approach 1:
The system implements a feedback mechanism where the measured average gray level is used to adjust the exposure time for each wafer. This feedback loop ensures the gray level remains within the defect detectable range while using a simple and efficient adjustment method that does not significantly increase system complexity.
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 efficient and appropriate defect inspection by ensuring the image gray level is within the detectable range, reducing the frequency of adjustments and improving defect detection accuracy.
Implementation Method 1
one surface of the principal surfaces of a wafer is irradiated with an infrared light, the other surface of the principal surfaces of the wafer is imaged
Data Source
AI summary
It is judged whether or not an average gray level of an image of a wafer W that is an inspection target and that has been imaged by the light receiving part 2 is in the defect detectable range. A control processing part 6a is configured to modify an exposure time in imaging the wafer W and to obtain an image of the wafer W again by the light receiving part 2 in the case in which it is decided that an average gray level of an image of the wafer W is not in a defect detectable range, and an image processing part 6b is configured to carry out a defect inspection based on an image of the wafer W in the case in which it is decided that an average gray level of the image of the wafer W is in the defect detectable range.