SEM Step Height Measurement via Focal Length Variation
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Solution Overview
Problem
Current methods for measuring the step height of fine patterns, such as atomic force microscopes (AFM) and optical CD measurement equipment, face limitations in precision and reliability due to probe wear and the requirement for uniform patterns, respectively.
Innovation Solution
A method and apparatus using a scanning electron microscope (SEM) that captures images of a device with varying focal lengths, converts them into gray-level histograms, and analyzes peak values to determine the step height between regions, enabling precise 3D depth measurement regardless of pattern repeatability or shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AFM contact-scanning method is used to measure etch depth, then measurement can be performed, but probe tip wears down leading to reduced measurement reliability
Solution Approach 1:
The patent replaces the mechanical contact-scanning method of AFM with a non-contact optical measurement method using SEM. The SEM captures images at different focal lengths to obtain depth information without physical contact, eliminating probe wear and maintaining both measurement precision and reliability over multiple measurements.
Solution Approach 2:
The patent introduces optical focus adjustment as an intermediary mechanism to indirectly measure depth. Instead of directly contacting the sample, the system uses focal length variations to encode depth information, which is then decoded through image analysis, providing reliable non-contact measurement.
2Reliability
If OCD measurement equipment is used to measure 3D shape, then non-contact scanning is achieved, but measurement is limited to uniformly repeated patterns only
Solution Approach 1:
The patent changes the measurement parameter from requiring pattern uniformity to utilizing focal length variations. By capturing images at multiple focal lengths and analyzing focus metrics, the system can measure diverse pattern types including non-uniform and non-repeated structures, significantly improving adaptability while maintaining non-contact reliability.
3Measurement precision
If multiple measurement methods are used to achieve both 2D CD and 3D depth measurement, then comprehensive measurement is possible, but equipment cost and complexity increase
Solution Approach 1:
The patent makes the SEM multi-functional by enabling it to perform both 2D critical dimension measurement and 3D depth measurement using the same instrument. By capturing images at different focal lengths and applying appropriate analysis methods, a single SEM system replaces the need for separate AFM and OCD equipment, reducing overall system complexity and cost.
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 allows for accurate and reliable measurement of step heights using a non-contact scanning method, reducing measurement errors and equipment costs by leveraging the SEM's high resolution and ability to measure 3D depths without additional equipment.
Implementation Method 1
obtain a SEM image which comprises a first SEM image region for the first region and a second SEM image region for the second region
Data Source
AI summary
A method of measuring a step height of a device using a scanning electron microscope (SEM), the method may include providing a device which comprises a first region and a second region, wherein a step is formed between the first region and the second region, obtaining a SEM image of the device by photographing the device using a SEM, wherein the SEM image comprises a first SEM image region for the first region and a second SEM image region for the second region, converting the SEM image into a gray-level histogram and calculating a first peak value related to the first SEM image region and a second peak value related to the second SEM image region, wherein the first peak value and the second peak value are repeatedly calculated by varying a focal length of the SEM, and determining a height of the step by analyzing a trend of changes in the first peak value according to changes in the focal length and a trend of changes in the second peak value according to the changes in the focal length.