Charged Particle Source with Spherical Virtual Cathode Control
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Solution Overview
Problem
Existing charged particle sources experience non-uniform electric field intensity distributions near the emitter tip end, leading to increased beam diameter and reduced spatial resolution under high current density conditions, which affects inspection sensitivity and length measurement capability in SEMs.
Innovation Solution
A charged particle source with a spherical virtual cathode surface where the virtual cathode surfaces for charged particles emitted from different positions on the emitter tip end match each other, ensuring a uniform electric field intensity distribution and a small light source diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an electron source with conical and columnar portions is used, then the energy width of particles is narrowed, but the electron source diameter increases leading to reduced spatial resolution
Solution Approach 1:
The invention employs a spherical surface portion at the tip end of the electron source instead of conical and columnar portions. This spherical geometry creates a more uniform electric field distribution in the vicinity of the emission surface, preventing the increase in electron source diameter that occurs with conical-columnar structures. The curved surface allows for better field uniformity across the emission area, maintaining both narrow energy width and small source diameter for high spatial resolution.
Solution Approach 2:
The invention optimizes specific geometric parameters of the electron source, including the curvature radius of the spherical surface portion and the angle of the conical portion. By carefully controlling these parameters (curvature radius ratio r/L between 0.05-0.3, conical angle θ between 10-30 degrees), the electric field distribution is optimized to achieve uniform field intensity while maintaining a compact source diameter, thus resolving the contradiction between energy width and spatial resolution.
2Measurement precision
If the electron source diameter is reduced to improve spatial resolution, then the beam diameter decreases, but the charged particle current decreases under high current density conditions
Solution Approach 1:
The invention creates a localized region of uniform electric field intensity at the emission surface by designing the tip geometry with a spherical surface portion. This local field uniformity ensures that even with a small source diameter, the electric field is distributed evenly across the emission area, enabling high current density without increasing the overall source diameter. The conical portion below the spherical surface provides a transition that maintains field uniformity while supporting higher currents.
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 stabilizes the electric field intensity over a wide range, reducing energy dispersion and allowing for a large charged particle current with a small source diameter, thereby enhancing spatial resolution and inspection sensitivity under high-angle current density conditions.
Implementation Method 1
a charged particle source having a spherical virtual cathode surface 10 from which charged particles are emitted
Implementation Method 2
electric field intensity distribution in the vicinity of an emitter tip end is uniform over a wide range
Data Source
AI summary
A charged particle source is provided that exhibits small energy dispersion for charged particle beams emitted under a high angular current density condition and allows stable acquisition of large charged particle currents even for a small light source diameter. The charged particle source has a spherical virtual cathode surface from which charged particles are emitted, and the virtual cathode surface for charged particles emitted from a first position on a tip end surface of an emitter and the virtual cathode surface for charged particles emitted from a second position on the tip end surface of the emitter match each other.