Wafer Separation Using Ultrafast Laser Detachment Regions
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Solution Overview
Problem
Conventional methods for splitting solids, such as sawing, result in material waste, thickness fluctuations, and high reworking costs, while laser-based methods face challenges with thermal stress and precision in separating thick or large solids.
Innovation Solution
A method using pico- or femtosecond lasers to modify the crystal lattice of solids, allowing for controlled cracking along a detachment region without chipping, by introducing laser beams through the surface of the solid to be separated, and utilizing a cooling device to manage thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sawing is used to separate solid layers, then the separation can be achieved, but material waste in the form of chips is produced and thickness fluctuation increases
Solution Approach 1:
The patent replaces the mechanical sawing system with a laser-based modification system. Instead of using a physical saw blade that mechanically cuts through the solid, the invention uses laser beams to modify the crystal lattice structure, creating controlled detachment regions that enable separation without mechanical contact. This substitution eliminates chip production and thickness fluctuation while maintaining separation capability.
Solution Approach 2:
The invention changes the physical state and structural parameters of the solid by modifying the crystal lattice through laser irradiation. By altering the lattice structure at the molecular level rather than mechanically removing material, the process achieves precise separation without the material loss and dimensional variability associated with traditional sawing methods.
2Manufacturing precision
If conventional laser heating is used to achieve separation, then separation can be achieved, but the solid distorts and expands due to high temperatures
Solution Approach 1:
The patent employs ultra-short pulsed laser technology (pico- or femtosecond pulses) that delivers energy in extremely brief, periodic bursts. This periodic action allows the laser to modify the crystal lattice through nonlinear optical absorption and stress accumulation without transferring significant thermal energy to the bulk material, thereby avoiding thermal expansion and distortion while achieving precise separation.
Solution Approach 2:
The ultra-short laser pulses interact with the material so quickly that the energy deposition and lattice modification occur before thermal diffusion can spread the heat to surrounding areas. This 'rushing through' the material's thermal response time enables precise localized modification without the harmful thermal effects of conventional continuous or long-pulse laser heating.
3Ease of manufacture
If laser beams are introduced via a surface not part of the layer to be separated, then the process can be simplified, but strong heating of the solid occurs causing distortion
Solution Approach 1:
The patent introduces laser beams through the surface of the layer to be separated (a different dimensional approach than conventional methods). By changing which surface serves as the entry point and combining this with ultra-short pulsing, the method achieves both process simplicity and high precision by directing energy exactly where needed without excessive thermal diffusion.
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
Enables precise and cost-effective splitting of solids without material waste, reducing thermal stress and distortion, and allowing for the separation of thick or large solids with improved precision and reduced reworking needs.
Implementation Method 1
modifying the crystal lattice of the solid by means of a modifying agent, in particular a laser, in particular a pico- or femtosecond laser
Implementation Method 2
as a result of the modifications, the crystal lattice cracks the regions surrounding the modifications
Implementation Method 3
utilizing a cooling device to manage thermal stress
Data Source
AI summary
A method for separating a solid body includes: providing a first solid body having opposite first and second surfaces and a crystal lattice, and that is at least partially transparent to a laser beam emitted by a laser; modifying a portion of the crystal lattice by the laser beam, the laser beam penetrating through the first surface, the modified portion of the crystal lattice extending in a plane parallel to the first surface, as a result of the modification, subcritical cracks are formed arranged in a plane parallel to the first surface, a plurality of the subcritical cracks forming a detachment region in the first solid body, the plurality of the subcritical cracks passing at least in some sections through the modified portion of the crystal lattice; and separating the first solid body along the detachment region to form a wafer and a second solid body.