Multi-Wavelength Charge Control for Charged Particle Inspection
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Solution Overview
Problem
Charged particle beam inspection systems, such as SEMs, face challenges in identifying defects in semiconductor devices due to charge accumulation on the wafer surface, which degrades image quality and makes it difficult to detect critical defects, especially when electron beams induce charging that is not effectively regulated.
Innovation Solution
The use of multiple light sources with different wavelengths, combined using dichroic mirrors or trichroic prisms, to project beams that penetrate and interact with the substrate at varying depths, generating thermal effects and modifying electrical properties, thereby controlling charge accumulation and improving signal-to-noise ratios during inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single wavelength light source is used for charge control, then the system structure is simple, but the ability to control charge at different depths is limited
Solution Approach 1:
The patent divides the charge control function into multiple wavelength components, where each wavelength targets specific depth regions or charge types. The light source system is segmented into multiple lasers (e.g., 405nm for surface, 532nm for intermediate depth, 1064nm for deep penetration), allowing independent optimization of each wavelength's parameters for specific charge control tasks at different depths.
Solution Approach 2:
The patent creates a multi-functional light source system where different wavelengths serve multiple purposes: some wavelengths primarily neutralize positive charge, others handle negative charge, and certain wavelengths can penetrate to different depths. This universal system can adapt to various inspection scenarios by selecting appropriate wavelength combinations, making the inspection system versatile for different material types and defect conditions.
2Measurement precision
If multiple wavelengths are used to control charge at different depths, then charge control effectiveness is improved, but the system complexity increases
Solution Approach 1:
The patent extends the charge control capability from a single-dimension (surface only) to multi-dimensional (depth-stratified) control by introducing wavelength as an additional dimension. Each wavelength penetrates to a specific depth range, creating a vertical dimension of charge control. This allows the system to address charge accumulation at multiple depth levels simultaneously, significantly improving defect detection accuracy for subsurface features.
Solution Approach 2:
The patent changes the optical parameter (wavelength) to achieve different penetration depths and interaction mechanisms with the substrate. By adjusting wavelength parameters, the system optimizes photon energy for specific depths: shorter wavelengths for surface charge, longer wavelengths for deeper penetration. This parameter-based control enables precise charge neutralization at targeted depths without increasing physical system complexity.
3Productivity
If higher beam current is used to improve inspection speed, then productivity increases, but charge accumulation worsens
Solution Approach 1:
The patent applies preliminary anti-action by using light to pre-neutralize or reduce charge accumulation on the substrate surface before the electron beam arrives. The light source continuously or periodically illuminates the inspection area, creating a charge-free or reduced-charge state in advance. This preliminary action prevents excessive charge buildup that would otherwise occur with high beam current inspection, allowing faster inspection speeds without image quality degradation.
Solution Approach 2:
The patent converts the harmful effect of charge accumulation into a beneficial process by using the same light that causes photoelectric emission to also serve as a charge neutralization mechanism. The light-induced photocurrent and thermal effects are harnessed to drain accumulated charges, transforming what was previously a detrimental side effect into a useful charge control mechanism that enables higher beam currents to be used safely.
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 enhances the ability to control physical properties at different depths within the substrate, improving defect detection accuracy and image quality by concurrently managing electrical and thermal effects, thus overcoming the limitations of charge accumulation and enhancing the contrast between defective and non-defective areas.
Implementation Method 1
The first wavelength may be selected to generate thermal effects in the portion of the substrate
Implementation Method 2
the optical beam may either induce a photocurrent or stimulate a leakage current so that ground or substrate electrons migrate to the inspection site and neutralize a positive charge
Implementation Method 3
When the electron beam is scanned over the surface pattern of a device, charging may be induced and accumulate on the device
Data Source
AI summary
An apparatus for and a method of inspecting a substrate in which a charged particle beam is arranged to impinge on a portion of the substrate and a first light beam having a first wavelength and a second light beam having a second wavelength different from the first wavelength are also arranged to impinge on the portion of the substrate.