Optical Height Detection for Semiconductor Wafer Focus Control
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Solution Overview
Problem
Existing optical height detection methods for semiconductor wafers suffer from detection errors due to reflectance differences between patterns, leading to inaccurate focus control and increased processing time in CD-SEM and SEM inspection apparatuses.
Innovation Solution
An optical height detection method using two-dimensional slit light projected diagonally onto the wafer, with a two-dimensional area sensor converting the slit image into an electrical signal and eliminating slit parts with large detection errors, allowing for accurate height detection by calculating symmetric waveforms and shift distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical height detection is performed using conventional methods, then the processing time is shorter, but the detection accuracy deteriorates due to reflectance differences between patterns
Solution Approach 1:
The invention extracts and eliminates the problematic slit parts that cause large detection errors from the optical height detection process. By identifying and removing these specific problematic regions from the measurement data, the system achieves higher accuracy without requiring complete re-measurement, thus minimizing time loss.
Solution Approach 2:
The invention implements a feedback mechanism where the detection results are analyzed to identify slit parts with large errors, and this information is used to adjust and improve subsequent measurements. The system uses the detected height information to refine the focus control process, creating a closed-loop system that improves accuracy while optimizing processing time.
2Measurement precision
If automatic focus control is performed using electron beam images, then the detection accuracy is improved, but the processing time increases significantly
Solution Approach 1:
The invention performs preliminary optical height detection to obtain initial height information before executing the full automatic focus control process using electron beam images. This preliminary action provides a starting point that reduces the search space and number of iterations required for subsequent electron beam-based focus optimization, thereby reducing overall processing time while maintaining accuracy.
Solution Approach 2:
The invention merges optical height detection with electron beam-based automatic focus control in a hybrid approach. The optical method provides rapid initial height estimation, while the electron beam method refines the focus accuracy. By combining these two methods strategically, the system achieves high focus accuracy with reduced total processing time compared to using electron beam images alone.
3Measurement precision
If the focal position is not accurately controlled, then the processing speed is maintained, but the measurement precision and inspection quality deteriorate
Solution Approach 1:
The invention replaces purely mechanical/electronic focus adjustment with an optical-based height detection system that provides faster and more accurate focal position determination. By using optical methods to determine wafer height and automatically adjust focus, the system achieves both high measurement precision and maintained throughput, eliminating the trade-off between accuracy and speed.
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
Significantly reduces detection errors and improves the accuracy of optical height detection, thereby shortening the processing time for focus control and enhancing the throughput of CD-SEM apparatuses and the quality of electron beam images in SEM inspection apparatuses.
Implementation Method 1
converting a two-dimensional slit image of the detected two-dimensional slit light into an electrical signal by a two-dimensional area sensor
Data Source
AI summary
The present invention provides an optical height detection method and electron beam apparatus to which the method is applied, in which the focusing accuracy of the CD-SEM apparatus, a SEM inspection apparatus, and others is improved by reducing detection errors and improving detection accuracy so as to improve the accuracy of the optical height detection method, and throughput of a CD-SEM apparatus or others is improved by reducing the processing time of automatic focus control performed based on the detected height according to the optical height detection method. An optical detection optical system projects two-dimensional slit light to a measurement object from diagonally above it, detects the light reflected by the measurement object, converts a detected two-dimensional slit image into an electrical signal by a two-dimensional area sensor, eliminates slit parts having a large detection error from the electrical signal, and detects the height of the measurement object.