Objective Lens Layout for Fast Large-FOV Electron Beam Scanning
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Solution Overview
Problem
Current charged particle beam apparatuses for semiconductor inspection are limited by slow throughput and inability to detect latent defects, particularly those under the surface layer, due to chromatic aberration and high voltage requirements that lead to arcing issues.
Innovation Solution
The system incorporates a magnetic and electrostatic lens objective system with a beam guiding tube, multiple deflection units, and a retarding electrode to control beam energy and direction, allowing for high-resolution and high-throughput scanning with reduced chromatic aberration and edge aberration, enabling detection of defects across a large field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If very high voltage is used to accelerate the charged particle beam for LFOV scan, then throughput is enhanced, but arcing problem occurs
Solution Approach 1:
The patent changes the voltage parameter from very high voltage to moderate voltage operation. The objective lens system is designed to focus charged particle beams at moderate acceleration voltages, eliminating arcing while maintaining LFOV scanning capability and throughput enhancement.
2Measurement precision
If multiple deflection units are added to reduce chromatic aberration and enable LFOV scan, then defect detection capability is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple deflection units (first and second deflectors) within a single objective lens assembly. The deflectors are integrated into the lens structure with precise spatial arrangement, merging the functions of focusing and deflection into a unified system rather than separate components.
Solution Approach 2:
The patent segments the deflection function into multiple stages with different deflectors positioned at specific locations within the objective lens. Each deflector handles specific aspects of beam steering, with the first deflector positioned upstream and the second deflector positioned downstream, allowing independent optimization of each component.
3Productivity
If beam current is increased for rapid defect inspection, then throughput is improved, but chromatic aberration increases reducing resolution
Solution Approach 1:
The patent optimizes the objective lens parameters including magnetic field strength, lens geometry, and operating voltage to minimize chromatic aberration. The lens is designed with specific pole piece configurations and gap dimensions that reduce sensitivity to beam energy spread, allowing high beam current operation without significant resolution degradation.
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 enhances defect detection capabilities, improving semiconductor manufacturing yield and throughput by enabling rapid and accurate identification of defects, including those hidden beneath the surface, while minimizing specimen damage and arcing risks.
Implementation Method 1
an objective lens including a yoke encompassing a coil, said yoke including a first pole piece and a second pole piece such that a magnetic field is leaked out from said first pole piece and second pole piece
Implementation Method 2
an electrostatic lens inside said objective and above said first deflector unit
Implementation Method 3
a first deflector unit, between said first pole piece and said second pole piece, for deflecting said charged particle beam to a first distance, a second deflector unit below said objective lens for deflecting said charged particle beam to a second distance
Data Source
AI summary
The device includes a beam source for generating an electron beam, a beam guiding tube passed through an objective lens, an objective lens for generating a magnetic field in the vicinity of the specimen to focus the particles of the particle beam on the specimen, a control electrode having a potential for providing a retarding field to the particle beam near the specimen to reduce the energy of the particle beam when the beam collides with the specimen, a deflection system including a plurality of deflection units situated along the optical axis for deflecting the particle beam to allow scanning on the specimen with large area, at least one of the deflection units located in the retarding field of the beam, the remainder of the deflection units located within the central bore of the objective lens, and a detection unit to capture secondary electron (SE) and backscattered electrons (BSE).