Detecting Blind Contact Defects via Voltage Contrast Analysis
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Solution Overview
Problem
As technology nodes shrink below 40 nm, traditional E-Beam inspection methods face challenges in detecting tiny electrical defects in contact/via plugs due to complex layout structures and misalignment issues, especially with voltage contrast variations in via plugs.
Innovation Solution
The method involves using an electron-beam inspection tool with a pixel size less than 0.1 μm to capture voltage contrast differences, performing image extraction based on target and background gray levels, and comparing grayscale values with a predetermined range to detect blind or quasi-blind contact/via plugs, utilizing hot spot, leap and scan, or continuous scan inspections to ensure accurate alignment and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional E-Beam inspection methods are used to detect tiny electrical defects in contact/via plugs, then the inspection can be performed on the chip surface, but the detection precision deteriorates due to complex layout structures and misalignment issues at technology nodes below 40 nm
Solution Approach 1:
The patent extracts and analyzes voltage contrast (VC) variations specifically from via plugs by comparing them with reference images. The method isolates the VC signal from the complex layout by performing image subtraction and analyzing only the VC difference, thereby separating the detection task from the complex surrounding structures.
Solution Approach 2:
The patent changes the inspection parameter from direct structural imaging to voltage contrast variation analysis. By monitoring VC variations rather than attempting to directly image the tiny structures, the method achieves better detection precision despite the complex layout and small feature sizes at 40 nm node and below.
2Area of stationary object
If large inspection field is used to inspect tiny defects, then the inspection area is increased, but the alignment precision deteriorates due to misalignment issues in E-Beam inspection
Solution Approach 1:
The patent uses a feedback mechanism where captured images are compared with reference images from the same location on a different die. The VC difference analysis provides feedback that highlights only the electrical defects, automatically compensating for minor alignment variations and enabling accurate defect detection across large inspection fields.
3Reliability
If voltage contrast inspection is performed on via plugs with complex layout structures, then electrical defects can be detected, but the monitoring complexity increases due to different pitches, length metal lines and metallic layers
Solution Approach 1:
The patent extracts the VC signal specific to via plugs by comparing images with and without the via structures. This extraction process isolates the relevant electrical defect information from the complex background of different metal lines and layers, simplifying the monitoring task while maintaining high detection reliability.
Solution Approach 2:
The patent introduces a reference image as an intermediary for comparison. By using a reference image from the same location on a different die, the method mediates the complex VC analysis, enabling reliable defect detection without being overwhelmed by the complexity of the via plug layout structures.
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 determines electrical defects in contact/via plugs, including quasi-blind issues, with improved alignment performance and sensitivity, even in complex layouts, by contrasting extracted images with layout designs and determining abnormal grayscale values within specific ranges.
Implementation Method 1
The E-Beam inspection (EBI) tool is currently used to obtain the image of the surface structure of a chip
Implementation Method 2
Voltage contrast (VC) inspection in EBI is widely utilized to capture electrical defects of contact/via plugs
Data Source
AI summary
A method for detecting an electrical defect of contact/via plugs is provided. In the method, the contact/via plugs are monitored by an electron-beam (E-Beam) inspection tool to capture an image with a VC (voltage contrast) difference, and then an image extraction is performed on the image with the VC difference, wherein the image extraction is based on Target gray level/back ground gray level. The extracted image is contrasted with a layout design base to obtain a blind contact or Quasi-blind issue of contact/via plugs. A grayscale value of the VC difference having the blind contact or Quasi-blind issue is compared with a determined range of grayscale value to determine whether the VC difference is abnormal.