Multi-Beam Charged Particle Optics for Fast Working Distance Control
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Solution Overview
Problem
Multi-beam charged particle systems for wafer inspection face challenges in efficiently changing the working distance (WD) without inducing unwanted effects on image resolution and fidelity, particularly when dealing with varying substrate thicknesses, and existing methods are too slow for high-throughput operations.
Innovation Solution
A method and system that utilize a control unit to compute and adjust multiple particle-optical component parameters simultaneously, allowing rapid changes in WD without mechanical movement, using interpolation from predetermined calibration values to maintain imaging specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the working distance is changed by moving the wafer stage in z-direction, then the working distance can be adjusted, but positioning inaccuracies including tilt are introduced
Solution Approach 1:
The patent replaces the mechanical wafer stage movement system with an electromagnetic field-based particle-optical system. Instead of physically moving the wafer stage in z-direction to change working distance, the system uses particle-optical components (lenses, deflectors) controlled by electric and magnetic fields to adjust the working distance optically, thereby eliminating mechanical positioning errors and tilt issues
Solution Approach 2:
The patent introduces particle-optical components as intermediaries between the wafer stage and the particle beam. These components (objective lens, field lenses, deflectors) act as mediators that enable working distance adjustment through field control rather than direct mechanical movement, isolating the wafer stage from the precision requirements of working distance adjustment
2Ease of operation
If the focusing effect of particle-optical lenses is changed to adjust working distance, then the working distance can be modified, but other effects such as rotation, magnification, and telecentricity also change
Solution Approach 1:
The patent divides the particle-optical system into functionally independent segments: objective lens for primary focusing, field lenses for field control, and deflectors for beam steering. Each segment can be adjusted independently to control specific parameters, allowing working distance adjustment without affecting other imaging specifications through coordinated control of these segmented components
Solution Approach 2:
The patent uses parameter changes in electric and magnetic fields to control particle-optical components. By independently adjusting field strengths and voltages applied to different components (objective lens current, field lens voltages, deflector currents), the system can change working distance while maintaining constant magnification, rotation, and telecentricity through coordinated parameter adjustment
3Manufacturing precision
If iterative methods are used to set particle-optical component effects, then the desired working distance can be achieved, but the process is too slow for wafer inspection tasks
Solution Approach 1:
The patent implements preliminary characterization of the particle-optical system where the relationships between component parameters and imaging specifications are pre-determined and stored. During actual wafer inspection, pre-calculated parameter sets are directly applied based on the desired working distance, eliminating the need for slow iterative adjustments and enabling rapid throughput while maintaining precision
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
Enables fast and efficient WD adjustments in multi-beam charged particle systems, ensuring high throughput and maintaining image quality by minimizing parasitic effects on resolution and fidelity.
Implementation Method 1
the particle-optical components provide electric and/or magnetic fields which act on the charged particles of the particle beam
Implementation Method 2
the particle-optical components provide electric and/or magnetic fields which act on the charged particles of the particle beam
Implementation Method 3
electric and/or magnetic fields which act on the charged particles of the particle beam
Implementation Method 4
the particle-optical component can be a particle-optical lens, which has a focusing effect on the particle beam
Data Source
AI summary
A multi-beam charged particle system and a method of setting a working distance WD of the multi beam charged particle system are provided. With the method, the working distance is adjusted while the imaging performance of a wafer inspection task is maintained by computing parameter values of components from predetermined calibration parameter values. The method can allow a relatively fast wafer inspection task even with a wafer stage with a fixed z-position parallel to an optical axis of the multi-beam charged particle system.