Secondary Projection Imaging System for Multi-Beam Electron Microscopy
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Solution Overview
Problem
Current multi-beam electron microscopy systems face challenges in achieving high inspection resolution and throughput due to limitations in secondary electron detection efficiency and cross-talk levels, particularly when landing energies and currents of beamlets vary, leading to compromised image quality and efficiency.
Innovation Solution
A secondary projection imaging system is developed for multi-beam apparatuses, incorporating a zoom lens, anti-scanning deflection unit, and field lenses to maintain high collection efficiency and low cross-talk levels, even with varying landing energies and currents, by adjusting imaging magnification and correcting for aberrations and misalignments.
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 invention divides a single high-current electron beam into multiple low-current beamlets, each maintaining sufficient spatial resolution while collectively achieving high throughput. The beam is segmented into N beamlets where each beamlet carries a fraction of the total current, avoiding the Coulomb effect that plagues high-current single beams while summing their detection signals to achieve high productivity.
2Productivity
If multiple electron beams are used to increase throughput, then productivity is improved, but device complexity increases
Solution Approach 1:
The invention employs a single multi-functional electron optical column that performs both beam generation and multi-beamlet formation, eliminating the need for multiple independent columns. The system uses a universal electron source and optical path that can generate N beamlets simultaneously, reducing device complexity while maintaining high throughput capability.
Solution Approach 2:
The invention merges multiple beam detection functions into a single detector that simultaneously collects secondary electrons from all N beamlets. This consolidation of detection functions into one unified system reduces the complexity that would arise from having N separate detection systems, while still achieving N-fold throughput improvement.
3Productivity
If beam current is increased to improve detection efficiency, then productivity is improved, but measurement precision worsens due to Coulomb Effect
Solution Approach 1:
The invention segments the total beam current into N smaller beamlet currents, where each beamlet operates at a current level that maintains low Coulomb effect and high spatial resolution. The sum of all beamlet currents equals the original high current, achieving high detection efficiency through parallel processing of multiple low-current beams rather than one high-current beam.
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
The system enables high-resolution imaging and increased throughput in semiconductor manufacturing by ensuring consistent detection efficiency and reduced cross-talk across varying conditions, enhancing the overall performance of multi-beam electron microscopy systems.
Implementation Method 1
an electron source to generate a primary electron beam along a primary optical axis
Implementation Method 2
a condenser lens below the electron source to focus the primary electron beam to a certain degree
Implementation Method 3
a source-conversion unit below the condenser lens to change the primary electron beam into a plurality of beamlets
Implementation Method 4
an objective lens below the source-conversion unit to focus the plurality of beamlets to image the plurality of first images onto the surface and therefore to form a plurality of probe spots on the surface
Implementation Method 5
a deflection scanning unit below the source-conversion unit to deflect the plurality of beamlets to scan the plurality of probe spots respectively over a plurality of scanned regions within an observed area on the surface
Implementation Method 6
a beam separator below the source-conversion unit to deflect the plurality of secondary electron beams to enter the secondary projection imaging system along a secondary optical axis
Implementation Method 7
means for focusing a plurality of charged particle beams emanated from a sample surface to a plurality of detection elements of the detection device respectively
Implementation Method 8
a projection lens to focus the plurality of secondary electron beams from the transfer plane onto a detection plane and form a plurality of secondary-electron spots thereon
Implementation Method 9
an anti-scanning deflection unit to deflect the plurality of secondary electron beams in step with the plurality of probe spots scanning over the plurality of scanned regions to maintain positions of the plurality of secondary-electron spots
Implementation Method 10
an electron detection device with a plurality of detection elements to detect the plurality of secondary electron beams respectively
Data Source
AI summary
A secondary projection imaging system in a multi-beam apparatus is proposed, which makes the secondary electron detection with high collection efficiency and low cross-talk. The system employs one zoom lens, one projection lens and one anti-scanning deflection unit. The zoom lens and the projection lens respectively perform the zoom function and the anti-rotating function to remain the total imaging magnification and the total image rotation with respect to the landing energies and/or the currents of the plural primary beamlets. The anti-scanning deflection unit performs the anti-scanning function to eliminate the dynamic image displacement due to the deflection scanning of the plural primary beamlets.