Laser Shockwave Surface Inspection for Non-Destructive Particle Detection
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Solution Overview
Problem
Existing methods for inspecting surfaces for nano-scale particle contamination are either destructive or unsuitable for detecting small particles on rough surfaces, leading to inaccurate readings and potential damage to sensitive substrates.
Innovation Solution
A non-destructive method using a focused light beam to generate a shockwave that dislodges nano-scale particles from the surface, which are then detected in an airborne state, allowing for accurate measurement of cleanliness without damaging the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser beam is focused close to the surface to dislodge particles, then particle removal effectiveness is improved, but substrate damage increases
Solution Approach 1:
The patent moves the focal point from the surface plane to a position above the surface in the third dimension. By focusing the laser beam at a distance of 0.1-10mm above the substrate surface rather than directly on it, the shockwave is generated in the gas phase above the surface, allowing effective particle dislodgement while preventing direct thermal damage to the substrate.
Solution Approach 2:
The patent introduces a gas medium (air or other gas) as an intermediary between the laser focal point and the substrate surface. The laser energy is absorbed by the gas molecules, creating a shockwave that propagates through the gas to dislodge particles, rather than directly heating the substrate. This gas intermediary protects the substrate from direct laser thermal damage.
2Object-affected harmful factors
If the focal point is positioned far from the surface, then substrate damage is reduced, but particle dislodgement effectiveness decreases
Solution Approach 1:
The patent optimizes the focal distance parameter to a specific range of 0.1-10mm above the surface. Within this range, the shockwave maintains sufficient intensity to dislodge particles while the distance is adequate to prevent substrate damage. The system may scan through different focal distances to find the optimal value for each substrate type.
Solution Approach 2:
The patent employs dynamic adjustment of the focal point position relative to the substrate surface. The optimal focal distance may vary depending on substrate properties, particle types, and inspection requirements, allowing the system to adapt the focal distance dynamically to balance particle removal effectiveness with substrate protection.
3Force
If laser energy is increased to enhance shockwave effect, then particle dislodgement improves, but thermal damage to substrate increases
Solution Approach 1:
The gas medium serves as a thermal buffer, absorbing the laser energy and converting it to mechanical shockwave energy rather than direct thermal energy on the substrate. This intermediary approach allows high laser energy to be used for particle dislodgement while the gas layer prevents excessive heat transfer to the substrate.
Solution Approach 2:
The patent utilizes phase transitions of gas molecules in the focal region. The laser energy causes rapid heating and expansion of gas molecules, creating a shockwave through this phase transition process. This converts optical energy to mechanical energy efficiently while limiting thermal damage to the substrate through the gas buffer zone.
4Device complexity
If scattered light detection is used for large particles, then detection simplicity is maintained, but detection accuracy for nano particles deteriorates
Solution Approach 1:
The patent replaces direct optical detection of particles with indirect detection via shockwave-induced particle ejection. Instead of relying on scattered light from particles (which is ineffective for nano particles), the system uses a laser-induced shockwave to physically eject particles from the surface, making them detectable by various particle counters and detectors that can accurately measure even nano-scale particles.
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 method effectively removes and detects nano-scale particles without substrate damage, providing reliable quantitative information on surface cleanliness, especially on rough surfaces, using controlled laser shockwave conditions to avoid damage.
Implementation Method 1
U.S. Pat. No. 5,023,424A describes an apparatus and method using laser induced shock waves to dislodge particles from a wafer surface
Implementation Method 2
a focused light beam is provided to cause a shockwave to dislodge particles from the surface
Data Source
AI summary
A method and system for inspecting a surface. A lighting device is configured to provide a light beam focused at a focal point at a distance from a surface to cause a shockwave reaching the surface for dislodging particles from the surface and causing the particles dislodged from the surface to become airborne particles. A particle detector is configured to detect the airborne particles dislodged by the shockwave from the surface. For example, this can be used for quantifying a cleanliness and/or contamination of the surface by surface-bound nanoparticles, which were at least present on the surface prior to the shockwave, based on a detected amount of the airborne particles, after the shockwave is applied.