Optical Wafer Characterization Using Up-Sampled Difference Images
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Solution Overview
Problem
Existing wafer inspection systems face challenges in achieving a balance between sensitivity and throughput, particularly in broadband plasma (BBP) inspection, where smaller pixels enhance sensitivity but reduce throughput, and larger pixels increase throughput but decrease sensitivity, leading to a compromise. Additionally, current methods introduce aliasing noise and limit the application of filters to difference images, affecting signal-to-noise ratio (SNR) and image alignment.
Innovation Solution
The system employs a processing unit to acquire target and reference images, apply a de-noising filter, and up-sample difference images to generate high-sensitivity images, using a spatial frequency filter to improve SNR and reduce noise, while maintaining throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If smaller pixels are used in BBP wafer inspection, then sensitivity is improved, but throughput deteriorates
Solution Approach 1:
The patent divides the inspection process into two distinct modes: a first inspection mode that captures images at lower resolution for high throughput, and a second inspection mode that captures images at higher resolution for high sensitivity. This segmentation allows the system to switch between modes based on defect detection needs, resolving the contradiction between sensitivity and throughput by applying each mode where it is most effective.
Solution Approach 2:
The patent implements dynamic switching between two inspection modes with different pixel resolutions. The system can transition from a first mode with larger pixels (higher throughput) to a second mode with smaller pixels (higher sensitivity) based on real-time inspection requirements. This dynamic adaptability allows the system to optimize both sensitivity and throughput across different inspection scenarios.
2Measurement precision
If filtering is applied to difference images in BBP inspection, then signal-to-noise ratio is improved, but filter application capacity is limited
Solution Approach 1:
The patent applies filtering operations to the original target and reference images before generating the difference image. By performing filtering in advance on the source images, the system improves the quality of the subsequent difference image without being constrained by the limited filtering capacity that would exist if filtering were applied only after difference image generation. This preliminary filtering action resolves the contradiction by enabling more comprehensive noise reduction while maintaining system simplicity.
Data Source
AI summary
A system includes a processing unit communicatively coupled to a detector array of an optical wafer characterization system. The processing unit is configured to perform one or more steps of a method or process including the steps of acquiring one or more target images of a target location on a wafer from the detector array, applying a de-noising filter to at least the one or more target images, determining one or more difference images from one or more reference images and the one or more target images, and up-sampling the one or more difference images to generate one or more up-sampled images. One or more wafer defects are detectable in the one or more difference images or the up-sampled images.