Electron Beam Inspection for Coma Aberration in Semiconductor Overlay
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Solution Overview
Problem
Conventional overlay inspection in semiconductor manufacturing is prone to alignment discrepancies due to coma aberration from light, resulting in inaccurate alignment of patterns between layers, despite the overlay mark being within tolerance.
Innovation Solution
A projection type electron beam inspection apparatus and method that uses an electron gun to form a larger circular or elliptical irradiation area on the sample surface, with secondary electrons detected to improve accuracy, employing components like Electron Bombardment-Charge Coupled Device (EB-CCD) and Multi Channel Plate (MCP) for enhanced imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical microscope is used for overlay inspection, then alignment can be performed, but coma aberration causes alignment disclination and reduces accuracy
Solution Approach 1:
The patent replaces the optical microscope system with an electron beam inspection system. The electron beam is irradiated onto the sample surface to obtain a secondary electron image, eliminating the coma aberration problem inherent in optical systems. This substitution of detection mechanism (from optical to electron-based) directly resolves the technical contradiction by removing the harmful optical aberration while maintaining alignment inspection capability.
Solution Approach 2:
The patent changes the fundamental parameter of the inspection system from optical wavelength to electron beam energy. By using electrons instead of light, the system operates under different physical principles that are not subject to optical aberrations. This parameter change enables high-precision alignment inspection without the harmful effects of coma aberration.
2Ease of operation
If overlay mark with different pattern size is used, then alignment can be performed, but the actual device pattern is shifted and exposed to light resulting in alignment disclination
Solution Approach 1:
The patent replaces the light-based optical inspection system with an electron beam-based inspection system. The electron beam is irradiated onto the sample surface to obtain a secondary electron image, which eliminates the issues of light exposure and alignment disclination. This substitution allows for accurate alignment inspection without the harmful effects of light-based methods on the actual device pattern.
3Measurement precision
If electron beam is used with larger irradiation area than pattern size, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent employs an electron beam inspection system that uses electrostatic lenses and a secondary optical system to form images on a detection plane. While this replaces the optical system with an electron-based system, it achieves superior measurement precision through the use of secondary electron detection and image processing, justifying the increased device complexity.
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 enables high-accuracy defect inspection and improved overlay detection in semiconductor manufacturing, reducing alignment errors and enhancing the precision of pattern alignment between layers.
Implementation Method 1
forming such an irradiation area on the sample surface by an electron beam generated from an electron gun
Implementation Method 2
forming an image on an electron detection plane of a detector from secondary electrons emanating from the sample surface in response to the irradiation of the electron beam
Implementation Method 3
a secondary optical system having an electrostatic lens for accelerating secondary electrons emanating from the sample surface
Implementation Method 4
at least one electrostatic lens for forming an image of the accelerated secondary electrons on a detection plane of a detector
Data Source
AI summary
Provided is a defect inspection apparatus and an inspection (or evaluation) method with highly improved accuracy, which would not be provided by the prior art, in the defect inspection apparatus used in a manufacturing process of a semiconductor device.Provided is a method for inspecting a sample surface with a projection type electron beam inspection apparatus, comprising the steps of: forming such an irradiation area on the sample surface by an electron beam generated from an electron gun 21 that has approximately a circular or elliptical shape of a size larger than a pattern on the sample surface; irradiating the electron beam substantially onto a center of the pattern on the sample surface; and forming an image on an electron detection plane of a detector from secondary electrons emanating from the sample surface in response to the irradiation of the electron beam for inspecting the sample surface.