Multi-Beam Electron Optics for Uniform Probe Spots
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Solution Overview
Problem
Conventional multi-beam apparatuses face challenges in flexibly varying currents and landing energies of probe spots, leading to pitch variations and non-uniformity of probe spots, which affect throughput and resolution in semiconductor defect inspection.
Innovation Solution
A multi-beam apparatus with a movable collimating lens to vary beamlet currents and a micro-lens-and-compensator array to compensate off-axis aberrations, along with a pre-beamlet-forming means to reduce Coulomb effects, ensuring uniform probe spots and high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single electron beam with large current is used to increase throughput, then productivity is improved, but manufacturing precision deteriorates due to Coulomb effect
Solution Approach 1:
The single electron beam is divided into multiple beamlets (e.g., 10-100 beamlets) that scan different regions simultaneously. Each beamlet operates at low current avoiding Coulomb effect, while the collective action of all beamlets achieves high throughput equivalent to a single high-current beam.
2Productivity
If multiple electron beams from multiple sources are used to increase throughput, then productivity is improved, but device complexity increases
Solution Approach 1:
Instead of using multiple physical electron sources, the patent uses a single electron source and creates multiple virtual sources through optical imaging. The electron optics system forms multiple images of the single source, each serving as a virtual source for a beamlet, thereby achieving multi-beam functionality with single-source simplicity.
3Productivity
If beam-limit openings are used to divide the electron beam into multiple beamlets, then productivity is improved, but manufacturing precision deteriorates due to pitch variations
Solution Approach 1:
The patent introduces feedback control through aberration compensation. The system measures and detects variations in beamlet parameters (current, position, focus) and uses compensation elements to correct these variations in real-time, ensuring uniform probe spots across all beamlets despite initial variations from the beam-splitting process.
4Manufacturing precision
If conventional electron optics elements are used to focus beamlets, then manufacturing precision is improved, but device complexity increases due to size
Solution Approach 1:
The patent transitions from conventional large-scale electron optics to micro-scale optics. By miniaturizing the optics elements to the micrometer dimension, the system achieves the same focusing function in a compact form factor that can be integrated close to the sample surface, enabling simultaneous focusing of multiple beamlets without requiring large complex optical paths.
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 flexible adjustment of beamlet currents and compensation of off-axis aberrations, enhancing throughput and resolution for defect inspection in semiconductor manufacturing.
Implementation Method 1
a movable collimating lens to vary beamlet currents... the movable collimating lens collimates the primary-electron beam
Implementation Method 2
an image-forming means with a plurality of electron optics elements... the plurality of beamlets is focused to form a plurality of parallel images of the electron source
Implementation Method 3
An electron source generates a primary-electron beam along a primary optical axis of the apparatus
Implementation Method 4
a beam separator... directs a plurality of secondary electron beams from the plurality of scanned regions into the secondary projection imaging system
Data Source
AI summary
A multi-beam apparatus for observing a sample with high resolution and high throughput and in flexibly varying observing conditions is proposed. The apparatus uses a movable collimating lens to flexibly vary the currents of the plural probe spots without influencing the intervals thereof, a new source-conversion unit to form the plural images of the single electron source and compensate off-axis aberrations of the plural probe spots with respect to observing conditions, and a pre-beamlet-forming means to reduce the strong Coulomb effect due to the primary-electron beam.