Electron Beam Imaging Charge Control via Periodic Field Reversal
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Solution Overview
Problem
Conventional electron beam imaging systems face challenges in controlling surface charging on insulating samples, leading to focus, distortion, and contrast variations, which can render defect detection unstable or impossible, especially as semiconductor device design rules shrink.
Innovation Solution
The method involves modulating an electric field at the sample by alternating between an extracting and a suppressing electric field during imaging and charge control phases, respectively, to balance and cancel out positive and negative charging patterns, using a system with a lens voltage source and substrate voltage source to control the objective lens and substrate holder voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electron beam imaging is performed on insulating samples, then imaging capability is achieved, but surface charging occurs causing focus, distortion and contrast variations
Solution Approach 1:
The patent applies periodic action by alternating between imaging modes and charge control modes. The system periodically switches between detecting secondary electrons (imaging mode) and detecting backscattered electrons (charge control mode) to maintain stable surface charge conditions. This periodic switching allows the system to achieve both high-resolution imaging and stable image quality by controlling surface charging through the charge control mode phases.
2Measurement precision
If design rules continue to shrink to improve resolution, then imaging precision improves, but charging effects become increasingly performance limiting
Solution Approach 1:
The patent implements feedback by using the charge control mode to monitor and control surface charge conditions. The system detects backscattered electrons during charge control mode to assess surface charge state, then uses this information to adjust subsequent imaging operations. This feedback mechanism allows the system to maintain high-resolution defect detection capability while compensating for charging effects that become more significant as design rules shrink.
Solution Approach 2:
The patent introduces an intermediary mechanism by using backscattered electron detection as a mediator to control surface charge. Instead of directly measuring surface charge, the system uses backscattered electrons as an intermediary signal to infer and control charge conditions. This intermediary approach enables precise control of charging effects while maintaining the ability to detect small defects at shrinking design rules.
3Reliability
If conventional separate pre-flooding method is used, then charge control is achieved, but system complexity and processing time increase
Solution Approach 1:
The patent merges the imaging function and charge control function into a single integrated system. Instead of using separate pre-flooding apparatus, the system combines secondary electron detection (imaging) and backscattered electron detection (charge control) into one electron beam column. This merging eliminates the need for separate flooding guns and reduces system complexity while maintaining effective charge control throughout the imaging process.
Solution Approach 2:
The patent applies universality by making the electron beam column perform multiple functions. The same electron beam and detection system are used for both imaging (secondary electron detection) and charge control (backscattered electron detection). This multi-functionality eliminates the need for dedicated charge control apparatus, reducing system complexity and integration requirements while maintaining effective charge management.
4Productivity
If imaging speed is increased to improve productivity, then defects processed per hour increases, but charging effects become more severe
Solution Approach 1:
The patent applies continuity of useful action by integrating charge control into the imaging process itself. Rather than performing separate pre-flooding steps that interrupt imaging, the system continuously performs both imaging and charge control functions during the same electron beam scanning process. The charge control mode is activated periodically during imaging, ensuring continuous surface charge management without interrupting the overall imaging workflow, thus maintaining high productivity while controlling charging effects.
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 stabilizes the surface charge, improving image quality by maintaining a low average charging pattern, thereby enhancing the ability to detect defects and prevent catastrophic damage from excessive charging.
Implementation Method 1
an electron beam is controllably scanned over a target area of a substrate with an objective lens
Implementation Method 2
the electric field at the substrate is modulated by reversing the polarity of the electric field
Implementation Method 3
scattered electrons emitted from a target area of the substrate are detected with a detector
Implementation Method 4
the electric field at the substrate is modulated by reversing the polarity of the electric field between an imaging phase and a charge control phase
Data Source
AI summary
One embodiment relates to a method of electron beam imaging of a target area of a substrate. During an imaging phase, an electron beam is controllably scanned over the target area of the substrate, and extracted secondary electrons are detected. An electric field at a surface of the substrate is changed from an original electric field after the imaging phase. During a charge control phase, the electron beam is controllably scanned over the target area of the substrate. The electric field at the surface of the substrate is reverted back to the original electric field after the charge control phase. The imaging and charge control frames are interleaved. Other embodiments and features are also disclosed.