Multi-lens array for field curvature correction in multi-beam e-beam inspection
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Solution Overview
Problem
Current electron beam inspection systems have limited throughput due to field curvature effects that cause focus shifts, resulting in blurred spot sizes at the outer edges of the scanning area, which limits the number of beams that can be used for inspection and the overall scalability of the system.
Innovation Solution
A multi-beam e-beam column with a multi-lens array that intentionally pre-distorts electron beams to compensate for focus shifts caused by downstream lenses, using stacked electrostatic plates with individually addressable potentials to produce multiple beamlets with varied focal points, ensuring precise focusing across the entire field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single electron beam is used for inspection, then focusing precision is maintained, but throughput is limited
Solution Approach 1:
The patent divides a single electron beam into multiple parallel beamlets using a multi-lens array, allowing simultaneous inspection of multiple areas. Each lens in the array focuses a portion of the electron source onto a distinct location on the target, enabling parallel processing while maintaining individual focus control for each beamlet
Solution Approach 2:
The multi-lens array acts as an intermediary device between the electron source and the target, manipulating the electron beams to achieve both multiplication and individual focusing. The array of lenses serves as a mediating structure that enables parallel beam generation while maintaining precise focus control for each beamlet
2Productivity
If multiple beams are used to increase throughput, then productivity improves, but field curvature effects cause focus shifts and blurred spots
Solution Approach 1:
The patent applies different focal properties to different regions of the multi-lens array. Each lens within the array is designed with specific local characteristics to compensate for field curvature effects at its particular location. This allows each beamlet to be precisely focused at its specific target location despite variations in the overall optical path
Solution Approach 2:
The multi-lens array pre-compensates for field curvature effects by designing lenses with varying focal lengths and optical properties before the beams reach the target. This preliminary correction ensures that when multiple beamlets traverse different paths, they all converge at their respective focal points with sharp focus, preventing blurred spots
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 approach significantly improves the throughput of the inspection system by maintaining precise focusing across the entire field of view, enabling the use of multiple beams and enhancing the scalability and efficiency of the inspection process.
Implementation Method 1
an electron source and a multi-lens array configured to produce a plurality of beamlets utilizing electrons provided by the electron source
Implementation Method 2
a multi-lens array configured to produce a plurality of beamlets utilizing electrons provided by the electron source
Data Source
AI summary
Multi-beam e-beam columns and inspection systems that use such multi-beam e-beam columns are disclosed. A multi-beam e-beam column configured in accordance with the present disclosure may include an electron source and a multi-lens array configured to produce a plurality of beamlets utilizing electrons provided by the electron source. The multi-lens array may be further configured to shift a focus of at least one particular beamlet of the plurality of beamlets such that the focus of the at least one particular beamlet is different from a focus of at least one other beamlet of the plurality of beamlets.