Wafer Surface Inspection Speed Control via Defect Density Feedback
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Solution Overview
Problem
Current surface inspection apparatuses using bright field optical systems face challenges in detecting defects on semiconductor wafers with high integration levels, leading to reduced reliability and throughput due to the need for precise and time-consuming defect inspections, especially when defects are concentrated on partial surfaces like the edge portions of wafers.
Innovation Solution
A surface inspection apparatus and method that adjusts scanning speed based on defect density, using a stage with a moving wafer, an optical system for image projection, an image acquisition system, image processing, and a defect-detecting unit to compute and compare defect densities, thereby varying the scanning speed to enhance defect detection reliability and throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high sensitivity image acquisition system is used for precise defect inspection, then measurement precision is improved, but inspection time increases and productivity decreases
Solution Approach 1:
The patent applies dynamics by making the scanning speed variable rather than constant. The inspection system dynamically adjusts scanning speed based on real-time defect density feedback - moving slower in high-defect-density areas to maintain detection precision, and faster in low-defect-density areas to improve overall throughput. This resolves the contradiction by making the system adaptive to local conditions rather than using a fixed slow speed throughout.
Solution Approach 2:
The patent changes the parameter of scanning speed based on defect density measurements. By continuously monitoring defect density and adjusting the scanning speed parameter accordingly, the system achieves both high precision where needed and high throughput where possible, resolving the contradiction between measurement precision and productivity.
2Productivity
If swath sampling with skip rule is applied to increase throughput, then productivity is improved, but defect detection reliability decreases
Solution Approach 1:
The patent implements feedback by using detected defect density to control scanning speed. The system continuously monitors defect density in scanned areas and feeds this information back to adjust subsequent scanning parameters. This feedback mechanism ensures that reliability is maintained in high-defect areas while allowing throughput to increase in cleaner areas, resolving the contradiction between productivity and reliability.
Solution Approach 2:
The system dynamically adjusts scanning behavior based on real-time defect density measurements. Rather than using a fixed skip rule that sacrifices reliability, the system adapts its scanning pattern dynamically - reducing skip intervals when defect density is high and increasing them when defect density is low, thus maintaining reliability while improving overall throughput.
3Productivity
If scanning speed is increased to improve productivity, then productivity is improved, but defect detection precision deteriorates
Solution Approach 1:
The patent applies local quality by making scanning speed location-dependent rather than uniform. Different regions of the wafer surface receive different scanning speeds based on their local defect density characteristics. High-defect-density regions receive slower scanning speeds for precise detection, while low-defect-density regions receive faster scanning speeds for improved throughput, thus resolving the contradiction between productivity and precision through spatially varying quality.
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
This approach increases the reliability of defect detection and productivity by adapting scanning speed to defect density, ensuring comprehensive detection of impurities on wafer surfaces and preventing errors in semiconductor manufacturing processes.
Implementation Method 1
an optical system for enlarging and projecting the surface of the wafer supported on the stage
Implementation Method 2
a bright field optical system for acquiring an image from light reflected from the wafer surface
Data Source
AI summary
A surface inspection apparatus and method increase wafer productivity, wherein to increase an efficiency of the surface inspection apparatus to detect defects during a scanning of the wafer surface, a scanning speed for a subsequent defect detection is varied according to an increase/decrease of defect density represented on a plurality of images acquired successively. When the density of defects is reduced, the scanning speed increases and a level of a skip rule increases, and when the density of defects increases, the scanning speed decreases and a level of the skip rule decreases to precisely detect defects, thereby increasing reliability, throughput, and productivity.