CD-SEM with BSE Imaging for Wafer Process Control
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Solution Overview
Problem
Current Critical Dimension Scanning Electron Microscope (CD-SEM) technologies face challenges in accurately measuring semiconductor wafers, particularly at advanced nodes below 28 nm, due to limitations in contrast and resolution, especially with High Aspect Ratio (HAR) structures and complex material stacks, leading to insufficient process control and yield issues.
Innovation Solution
Concurrent performance of CD-SEM measurements and Back Scattered Electron (BSE) imaging, with Grey Level image analysis, to enhance material property detection and defect inspection, enabling precise control of semiconductor wafer fabrication processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Secondary Electron (SE) imaging is used for CD-SEM measurements, then topographical information is obtained with high resolution, but material contrast and bottom signal detection are insufficient
Solution Approach 1:
The patent combines SE imaging and BSE imaging into a single integrated measurement system. The semiconductor wafer is scanned with an electron beam, and both SE and BSE signals are collected simultaneously by separate detectors. The processing unit then fuses these two types of images to generate comprehensive measurements that include both topographical details from SE and material contrast information from BSE, thereby resolving the contradiction between resolution and material contrast detection.
Solution Approach 2:
The patent introduces BSE imaging as an intermediary technique to supplement SE imaging. While SE provides topographical information, BSE acts as an intermediary that penetrates deeper into the structure and provides material composition contrast. The combination of these two imaging modes allows the system to overcome the limitations of SE alone in detecting material properties and bottom signals of HAR structures.
2Measurement precision
If SE imaging is used at 28 nm technology and below, then high resolution is achieved, but bottom signal detection is lost due to HAR structures
Solution Approach 1:
The patent merges SE imaging and BSE imaging to simultaneously achieve high resolution and reliable bottom signal detection. The BSE detector specifically captures backscattered electrons that provide information from deeper layers, including the bottom of HAR structures. This combined approach ensures that both the high-resolution surface topology and the underlying material structure are reliably detected, even at 28 nm technology nodes and below.
3Measurement precision
If visual analysis by human operators or destructive material analysis is performed, then accurate inspection is achieved, but productivity and cost are reduced
Solution Approach 1:
The patent implements an automated inspection system that performs both SE and BSE imaging and processing without human intervention. The integrated system automatically captures images from both imaging modes, processes the data through algorithms that fuse the information, and generates measurements and defect detections. This self-service automated approach maintains high inspection accuracy while dramatically improving productivity by eliminating manual analysis steps and enabling inline process control.
4Measurement precision
If edge-based measurements are used, then topographical measurement is achieved, but material and non-topographic properties of deep layers are missed
Solution Approach 1:
The patent merges edge-based SE measurements with BSE imaging to simultaneously obtain both topographical edge information and material properties. The SE component provides precise edge location and critical dimension measurements, while the BSE component provides material composition and density information from deep layers. The processing unit integrates these complementary data sources to generate comprehensive measurements that include both geometric and material properties.
Solution Approach 2:
The patent adds another dimension of information by incorporating BSE imaging alongside traditional SE edge-based measurements. While SE operates primarily in the topographical dimension, BSE adds the material composition dimension. This multi-dimensional approach allows the system to measure both the geometric edges and the underlying material properties, providing a more complete characterization of the semiconductor structure.
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 provides cost-effective, non-destructive, high-resolution, and high-throughput process control for semiconductor wafer fabrication, improving yield and accuracy by integrating BSE imaging with CD-SEM metrology, effectively addressing limitations in existing technologies.
Implementation Method 1
The CDSEM measurements are extracted from top-down images based on secondary electron collection while scanning the specimen
Implementation Method 2
The key at BSE imaging is the collection of only the back scattered electrons (BSE) from outermost specimen surface
Data Source
AI summary
A Critical Dimensions Scanning Electron Microscope (CD-SEM) is described that comprises a unit for performing CD-SEM measurements of a semiconductor wafer, a BSE imaging unit for obtaining a Grey Level image (GL) of the wafer, and a unit for GL analysis and for processing the GL analysis results with reference to results of the CD-measurements.