Focal-Line Laser Machining for Clean Brittle Substrate Separation
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Solution Overview
Problem
Existing methods for laser-based machining of brittle materials, such as semiconductor wafers and glass elements, face issues like particle formation, microcracks, melted edges, non-uniform kerfs, and slow process rates due to heat-induced crack formation and ablation.
Innovation Solution
A method using a pulsed laser with a wavelength where the material is transparent, generating a focal line instead of a focal point, with carefully controlled laser parameters to induce absorption and thermal stress for precise crack formation along the focal line, avoiding ablation and melting, and allowing for high-speed separation with minimal material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser with high absorption wavelength or high power is used to ablate material, then material separation is achieved, but particle formation and microcracks occur due to ablation and heat input
Solution Approach 1:
The patent changes the laser wavelength parameter to one where the material is essentially transparent (not highly absorbing), and controls the pulse duration to be in the picosecond range. This parameter change prevents ablation and heat-induced microcracks while still achieving material separation through controlled fracture, thereby eliminating particle formation and microcracks without sacrificing separation effectiveness.
Solution Approach 2:
The patent employs periodic pulsed laser action with picosecond pulse duration and controlled repetition rates. This periodic action allows the material to cool between pulses, preventing heat accumulation and melt formation, while the cumulative effect of multiple pulses creates the desired fracture pattern for clean separation without harmful side effects.
2Manufacturing precision
If a laser focal point is used to create internal damage, then damage is concentrated at a specific depth, but complete thickness separation requires repeated processing at different depths which slows process rate
Solution Approach 1:
The patent transitions from creating a zero-dimensional focal point to creating a one-dimensional focal line that extends through the material thickness. This dimensional change allows the laser to create a continuous fracture path through the entire material thickness in a single pass, eliminating the need for repeated processing at different depths and significantly increasing the process rate while maintaining precise fracture control.
Solution Approach 2:
The patent creates a preliminary fracture path along the entire desired separation line through the material thickness before complete separation occurs. This preliminary action of creating a continuous crack path through controlled tensile stress enables the material to separate cleanly along the intended line without requiring multiple passes, thereby improving both precision and productivity.
3Productivity
If high average laser power is used for material ablation, then separation is achieved, but material must be evaporated which requires significant energy input
Solution Approach 1:
The patent replaces the thermal-mechanical ablation process with an optical-mechanical fracture process. Instead of using high energy to vaporize material through heating, the patent uses optical fields to induce tensile stresses that propagate controlled fractures. This substitution dramatically reduces energy consumption while achieving the same separation result, as fracture requires far less energy than phase change and vaporization.
Solution Approach 2:
The patent changes the laser parameters from continuous wave or long-pulse high-power operation to picosecond pulsed operation at wavelengths where material is transparent. This parameter change shifts the interaction mechanism from thermal ablation to optical field-induced fracture, reducing the average power requirement while maintaining separation effectiveness.
4Productivity
If laser-induced crack formation is used for separation, then material can be separated, but crack propagation is uneven resulting in rough separation surfaces that require subsequent machining
Solution Approach 1:
The patent employs feedback control by monitoring the fracture propagation in real-time and adjusting laser pulse parameters dynamically. The system detects the fracture front position and controls the timing and intensity of subsequent pulses to maintain uniform crack propagation, ensuring smooth separation surfaces without the need for additional machining while preserving high productivity.
Solution Approach 2:
The patent maintains continuous useful action by using overlapping picosecond pulses that continuously drive fracture propagation along the entire separation line. This continuous action ensures uniform crack development throughout the material thickness, producing smooth separation surfaces with high precision while maintaining rapid processing speeds.
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 achieves clean, straight cuts with minimal cracking and no material loss, enabling high-speed separation of brittle materials without particle formation or melted edges, and allows for precise control over cut angles and geometry.
Implementation Method 1
a pulsed laser with a wavelength where the material is transparent, generating a focal line instead of a focal point, with carefully controlled laser parameters to induce absorption and thermal stress
Implementation Method 2
induce absorption and thermal stress for precise crack formation along the focal line
Implementation Method 3
induce absorption and thermal stress for precise crack formation along the focal line, enabling high-speed separation of brittle materials
Data Source
AI summary
A method for laser-based machining of a flat substrate, to separate the substrate into a plurality of sections, in which the laser beam of a laser is directed at the substrate using an optical arrangement, which is positioned in the beam path of the laser. The optical arrangement forms a laser beam focal line that is extended as viewed along the beam direction and the substrate is positioned relative to the laser beam focal line such that an induced absorption is produced in the material of the substrate along a section of the laser beam focal line that is extended as viewed in the beam direction.