Charged Particle Beam Apparatus for High Throughput Inspection
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Solution Overview
Problem
Conventional low-voltage scanning electron microscopes (LVSEM) face challenges in achieving high spatial resolution and throughput for defect inspection in semiconductor manufacturing, particularly for 3-D integration and through-silicon-via (TSV) defect inspection, due to limitations in probe current and field of view, which result in increased probe spot sizes and off-axis aberrations, affecting image uniformity and collection efficiency.
Innovation Solution
The design of a charged particle beam apparatus with a magnetic condenser lens and objective lens configuration, including a retarding electrode and deflection unit, to focus primary electrons and collect secondary and backscattered electrons without crossovers, allowing for a larger probe current and field of view while reducing Coulomb effects and geometric aberrations, and enhancing BSE collection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If probe current and field of view are increased to improve throughput for TSV defect inspection, then productivity is improved, but probe spot size increases and imaging resolution deteriorates
Solution Approach 1:
The patent divides the beam path into multiple segments with dedicated focusing elements. A condenser lens system with multiple aperture plates segments the beam current control, while the objective lens with its field stop segments the field of view. This segmentation allows independent optimization of probe current (for throughput) and probe spot size (for resolution) by controlling different portions of the beam through different optical paths.
Solution Approach 2:
The patent applies local quality by using a field stop aperture that limits the field of view to only the necessary inspection area. This allows the majority of the beam current to be utilized while maintaining a small effective probe spot size only where needed for high-resolution imaging. The field stop creates a localized region of high quality imaging within a larger field of view, enabling both high throughput and high resolution simultaneously.
2Productivity
If probe current is increased to improve throughput, then productivity is improved, but Coulomb interactions increase and probe spot size enlarges
Solution Approach 1:
The patent extracts the harmful Coulomb interactions by using a condenser lens system with multiple aperture plates that spatially separate beam electrons. By dividing the beam into multiple smaller sub-beams that are focused independently, the patent reduces the density of electrons in any single location, thereby reducing Coulomb interactions. This allows high total probe current to be achieved while maintaining small probe spot size through the extracted and redistributed beam paths.
Solution Approach 2:
The patent transitions from a single-dimensional beam control approach to a multi-dimensional approach by using multiple aperture plates at different positions in the beam path. This creates additional spatial dimensions for beam control, allowing the patent to manage probe current and probe spot size independently through the multi-dimensional optical path created by the stacked aperture plates and condenser lens system.
3Productivity
If field of view is increased to improve throughput, then productivity is improved, but off-axis aberrations increase and image uniformity deteriorates
Solution Approach 1:
The patent applies preliminary action by using a field stop aperture placed before the sample to pre-limit the field of view to the necessary inspection area. This preliminary limitation of the field of view prevents off-axis aberrations from affecting the entire beam path, as only the necessary central region is utilized. The field stop prepares the optical path in advance to avoid aberrations, enabling high throughput within the limited field while maintaining excellent image uniformity.
4Manufacturing precision
If probe spot size is reduced to improve imaging resolution, then manufacturing precision is improved, but probe current decreases and throughput deteriorates
Solution Approach 1:
The patent uses a nested structure with multiple aperture plates stacked at different positions in the beam path, similar to nested dolls. Each aperture plate is nested within the beam path defined by the previous plates, creating a hierarchical control structure. This nesting allows the patent to control probe current at multiple levels while maintaining a small probe spot size, thereby achieving both high imaging resolution and high throughput through the nested aperture configuration.
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 enables high imaging resolution and throughput for large probe currents and fields of view, effectively addressing the limitations of prior art by minimizing probe spot size and off-axis aberrations, and improving the collection efficiency of secondary and backscattered electrons.
Implementation Method 1
The magnetic condenser lens and the magnetic objective lens are both aligned with the optical axis. The magnetic condenser lens and the magnetic objective lens focus the primary charged particle beam to forms a focused probe spot onto the surface of the sample
Implementation Method 2
The retarding electrode and the sample are electrically excited to generate a retarding field therebetween so that primary charged particles are decelerated to land on a surface of the sample with kinetic energies lower than 5 keV
Implementation Method 3
The deflection unit comprises at least one electrostatic deflector and one of the at least one electrostatic deflector is configured to generate an electrostatic deflection field superimposed onto a magnetic field of the magnetic objective lens along the optical axis
Implementation Method 4
The charged particle source and the accelerating electrode are excited to generate an accelerating field therebetween to accelerate the primary charged particles
Implementation Method 5
Coulomb interactions among primary electrons get stronger with decrease in electron kinetic energy, and the effect (Coulomb Effect) due to the Coulomb interaction will enlarge the probe spot size
Data Source
AI summary
The present invention provides a charged particle beam apparatus which employs LVSEM to inspect sample surface with a throughput much higher than the prior art. The high throughput is realized by providing a probe current and a FOV both several times of those of the prior art. Accordingly several means are proposed to avoid obvious degradation of image resolution due to the increases in Coulomb effect and geometric aberrations, and increase efficiency and uniformity of secondary charged particle collection.