Multi-Detector Electron Optics for Wide-FOV Defect Imaging
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Solution Overview
Problem
Current electron microscope systems face challenges in achieving high accuracy and throughput for defect inspection of integrated circuits due to low combined detection efficiencies of secondary and backscattered electrons, particularly for complex structures like 3D NAND devices, where simultaneous high-quality imaging of surface and buried layer information is required.
Innovation Solution
An electron beam apparatus with a compound objective lens comprising a magnetic and electrostatic lens, along with multiple electron detectors strategically positioned to enhance signal electron collection efficiency, including a first detector upstream from the magnetic lens polepiece, a second detector upstream, and a third detector downstream, allowing for efficient detection of secondary and backscattered electrons across a range of emission angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple electron detectors are used to maximize collection efficiency of secondary and backscattered electrons, then the detection of surface information from secondary electrons and buried layer information from backscattered electrons is improved, but the combined detection efficiencies remain low and image quality is inadequate
Solution Approach 1:
The detection system is divided into multiple specialized detectors positioned at different locations: an in-lens detector for secondary electrons, an upper detector for backscattered electrons, and a through-lens detector for medium-angle backscattered electrons. Each detector is optimized for specific electron types and angles, collectively achieving comprehensive signal collection that resolves the image quality inadequacy
Solution Approach 2:
The patent introduces spatial dimensionality by positioning detectors in three-dimensional space around the electron optical axis at different distances and angles. This multi-dimensional arrangement allows simultaneous detection of electrons with different emission angles and energies, transforming the detection capability from a single-point measurement to a multi-point spatial distribution that captures comprehensive sample information
2Measurement precision
If detectors are positioned closer to the sample to increase signal collection, then detection efficiency is improved, but detectors are exposed to electrostatic fields that can cause electrical damage
Solution Approach 1:
A polepiece is introduced as an intermediary component between the electrostatic field source and the detectors. The polepiece acts as a field-shielding barrier that blocks harmful electrostatic field lines while allowing electron signals to pass through, enabling detectors to be positioned close to the sample for maximum signal collection without direct exposure to damaging electric fields
Solution Approach 2:
The patent converts the potentially harmful electrostatic field into a beneficial focusing mechanism. By carefully designing the detector positioning and polepiece geometry, the electrostatic field that could damage detectors is transformed into a controlled field that helps focus and guide electron signals toward the detectors, turning a harmful factor into an asset for signal enhancement
3Measurement precision
If the opening of the first electron detector is made smaller to improve detection precision, then the detection of medium and large emission angle backscattered electrons is enhanced, but the field-of-view and signal electron distribution are limited
Solution Approach 1:
The detection system uses multiple detectors with different opening sizes and positions: the first detector has a smaller opening for precise medium and large angle backscattered electron detection, while the second and third detectors have larger openings to capture a broader field-of-view and complementary electron signals. This segmented approach allows each detector to specialize in specific angular ranges without compromising overall detection coverage
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 configuration significantly improves image quality and defect inspection efficiency by enhancing the detection of medium and large emission angle backscattered electrons, maintaining high resolution and throughput while minimizing electrical damage to detectors.
Implementation Method 1
a magnetic lens comprising a cavity configured to allow the primary electron beam to pass through
Implementation Method 2
a compound objective lens comprising a magnetic lens and an electrostatic lens
Implementation Method 3
a first electron detector configured to detect a first portion of a plurality of signal electrons generated from a sample
Data Source
AI summary
Systems and methods of imaging a sample using a charged-particle beam apparatus are disclosed. The charged-particle beam apparatus may include a compound objective lens comprising a magnetic lens and an electrostatic lens, the magnetic lens comprising a cavity, and an electron detector located immediately upstream from a polepiece of the magnetic lens and inside the cavity of the magnetic lens. In some embodiments, deflectors may be located between the electron detector and the opening of the polepiece adjacent to the sample to achieve a large field of view. Electron distributions among the detectors can be manipulated without changing the landing energy by changing the potential of the control electrode(s) in the electrostatic objective lens. The electron source can be operated with several discrete potentials to cover different landing energies, while the potential difference between electron source and the extractor is fixed.