Wafer Inspection Using Multi-Channel Detection for Small Defects
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Solution Overview
Problem
Current wafer inspection systems face limitations in sensitivity, particularly when detecting small defects on both smooth and rough surfaces, as the scattering of light from rough surfaces interferes with the detection of smaller defects, leading to a low signal-to-noise ratio and reduced throughput.
Innovation Solution
A system that includes an illumination subsystem directing light to a spot on the wafer at an oblique angle, with a first detection subsystem collecting light from one portion and a second detection subsystem simultaneously collecting and separating light from different portions of the spot across a limited azimuthal angle range, using multi-anode photomultiplier tubes and optical fibers to enhance sensitivity and reduce background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the spot size on the wafer is decreased to increase sensitivity for detecting small defects, then the signal-to-noise ratio improves, but the throughput of the inspection system decreases
Solution Approach 1:
The detection subsystem is divided into multiple detection channels, each detecting light from a different portion of the spot. This segmentation allows the system to maintain a larger spot size for high throughput while achieving high sensitivity through multiple smaller detection zones, effectively resolving the contradiction between spot size and detection capability.
2Measurement precision
If multiple detection channels are used to increase sensitivity, then the signal-to-noise ratio improves, but the device complexity increases
Solution Approach 1:
The multiple detection channels share common optical components such as the illumination source and collection optics, allowing a single system to perform multiple detection functions simultaneously. This multi-functionality approach increases sensitivity through multiple channels while minimizing the increase in overall device complexity by reusing components.
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
The system achieves enhanced sensitivity for detecting small defects on both smooth and rough surfaces while maintaining high throughput by reducing background scattering and improving the signal-to-noise ratio through the use of multiple detection channels and optical separation techniques.
Implementation Method 1
detect light scattered from different portions of a single TO spot obliquely illuminated on a wafer
Implementation Method 2
a detection subsystem configured to separately and simultaneously detect light scattered from different portions of a single TO spot
Data Source
AI summary
Systems and methods for inspecting wafers are provided. One system includes a detection subsystem configured to separately and simultaneously detect light scattered from different portions of a single spot obliquely, or normally, illuminated on a wafer and to separately generate output responsive to the separately detected light that can be used to detect defects on the wafer. The system can, therefore, effectively perform a multi-spot type of inspection of the wafer using only a single obliquely or normally illuminated spot on the wafer.