Charged Beam Shape Control for High-Speed Defect Inspection
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Solution Overview
Problem
Conventional SEM-based defect inspection techniques face a trade-off between inspection speed and resolution, as increasing speed degrades resolution due to the physical limitations of electron beam scanning, making it difficult to simultaneously achieve high-speed and high-resolution defect detection.
Innovation Solution
A defect inspection apparatus and method that control the shape of the charged beam to have a smaller width in one direction than another, while maintaining a consistent cross-sectional area, allowing for optimized scanning directions to improve resolution and speed by adjusting the beam shape using an astigmatism corrector and aligner, enabling high-speed scanning with reduced blur and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the electron beam scanning speed is increased to improve inspection speed, then productivity increases, but the resolution deteriorates due to the physical limitations of electron beam scanning
Solution Approach 1:
The patent segments the inspection process into multiple passes with different beam shapes. A first inspection uses a conventional circular beam at high speed for initial defect detection, while a second inspection uses an elliptical beam with reduced width in the scanning direction for high-resolution verification of suspected defects. This segmentation allows the system to achieve both high productivity and high measurement precision by applying different inspection strategies to different inspection stages.
Solution Approach 2:
The patent dynamically adjusts the beam shape from a circular cross-section during high-speed initial inspection to an elliptical cross-section with reduced width in the scanning direction during resolution-critical inspection. This dynamic adaptation of beam parameters allows the system to optimize for speed when resolution requirements are less stringent and switch to optimization for resolution when detailed examination is needed, thereby resolving the contradiction between inspection speed and resolution.
2Productivity
If a conventional circular beam is used for high-speed scanning, then inspection speed improves, but resolution in the scanning direction deteriorates due to beam width
Solution Approach 1:
The patent introduces asymmetry into the beam cross-section by transforming it from a circular shape to an elliptical shape, where the width in the scanning direction is reduced while the width in the non-scanning direction is increased. This asymmetric beam configuration allows the system to maintain high scanning speed while achieving improved resolution in the critical scanning direction, directly resolving the contradiction between speed and precision.
Solution Approach 2:
The patent changes the geometric parameters of the electron beam by controlling the astigmatism corrector to produce an elliptical beam with specific width ratios. By adjusting the beam width in the scanning direction to be smaller than in the non-scanning direction, the system achieves improved resolution without sacrificing inspection speed, as the reduced beam width in the scanning direction compensates for the effects of rapid scanning.
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 enhances defect detection sensitivity and throughput by improving resolution in critical directions while maintaining inspection speed, effectively addressing the limitations of conventional SEM methods.
Implementation Method 1
scanning the top of the wafer with an electron beam, using an SEM image of the circuit pattern obtained by detecting resultant secondary electrons, reflected electrons and back scattering electrons
Implementation Method 2
controlling a shape of the charged beam applied to the sample so as to cause a beam width in a first direction perpendicular to an optical axis to differ from a beam width in a second direction perpendicular to the optical axis and the first direction
Data Source
AI summary
A defect inspection method includes generating and applies a charged beam to a sample with patterns; controlling a shape of the charged beam so that a beam width in a first direction perpendicular to an optical axis differs from a beam width in a second direction perpendicular to the optical axis and the first direction, while substantially maintaining a cross-sectional area of the beam; scanning the sample with the charged beam having the controlled shape; and detecting charged particles from the sample by irradiation of the charged beam and detects a defect of the patterns. Assuming that the beam width of the charged beam in the first direction is smaller than that in the second direction, the first direction is set to a direction in which an interval between adjacent patterns becomes a minimum value and the sample is scanned in the second direction.