Wafer Defect Detection via Dynamic Focus Image Combination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current semiconductor wafer inspection systems face challenges in detecting small defects due to increased speckle noise from coherent light sources, which reduces the signal-to-noise ratio and limits defect detection ability as wafer design rules shrink.
Innovation Solution
The method involves scanning a wafer using different optical states of an inspection system, specifically varying the focus while keeping other optical parameters constant, to generate and combine image data, thereby reducing speckle noise and enhancing the signal-to-noise ratio for defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser light source is used to generate bright light at small wavelengths, then the resolution of the inspection system is improved, but speckle noise increases and reduces the signal-to-noise ratio
Solution Approach 1:
The patent makes the optical system dynamic by varying the focus setting between two different values. This dynamic adjustment changes the optical state to generate two different image data sets, which when combined, reduce speckle noise while preserving the benefits of coherent light illumination for high-resolution inspection.
Solution Approach 2:
The patent merges two image data sets acquired at different focus settings into a single combined data set. This combining process eliminates speckle noise through correlation while maintaining the high resolution enabled by coherent light, thus resolving the contradiction between resolution improvement and speckle noise reduction.
2Measurement precision
If the wavelength of inspection systems is decreased to improve resolution, then smaller defects can be detected, but incoherent light sources cannot produce sufficient brightness
Solution Approach 1:
The patent changes the focus parameter of the optical system between two different values while maintaining coherent light illumination. This parameter variation enables noise reduction without requiring a change to incoherent light sources, thus preserving both brightness and detection capability for small defects.
3Object-generated harmful factors
If aperture is moved in the pupil plane to reduce speckle noise, then speckle is reduced, but the resolution of the optical system decreases
Solution Approach 1:
Instead of moving the aperture in the pupil plane, the patent changes the focus parameter of the optical system. This alternative parameter change achieves speckle noise reduction through correlation of multiple image data sets while preserving the optical system's resolution capability.
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 effectively reduces speckle noise and improves the signal-to-noise ratio, enabling more accurate detection of defects that may not be visible in individual optical states, thereby enhancing defect capture rates and reducing false counts.
Implementation Method 1
laser light sources generate coherent light. Such light is disadvantageous for inspection since coherent light can produce speckle in images of a wafer. Since speckle is a source of noise in the images, the signal-to-noise ratio (S/N) in images generated by inspection systems will be reduced by speckle.
Implementation Method 2
for inspection systems that are designed to operate at smaller wavelengths, a more suitable light source is a laser light source that can generate relatively bright light at relatively small wavelengths. However, laser light sources generate coherent light.
Data Source
AI summary
Systems and methods for detecting defects on a wafer are provided. One method includes combining first image data and second image data, generated using different output generated using different values for focus of an inspection system, corresponding to substantially the same locations on the wafer thereby creating additional image data for the wafer and detecting defects on the wafer using the additional image data.