Laser-Assisted Substrate Separation for Thin Silicon Wafers
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Solution Overview
Problem
Current methods for producing thin substrates from brittle and hard materials like silicon, sapphire, and ceramics are inefficient, leading to high material loss, long process times, and high costs due to sawing and polishing requirements, and are not suitable for producing monocrystalline wafers with high contour accuracy.
Innovation Solution
A laser-assisted method that perforates a partially transparent substrate block with focused laser pulses to create a fracture surface, allowing for the separation of thin substrates with minimal material loss and high contour accuracy, enabling the production of monocrystalline, polycrystalline, and amorphous substrates with precise thickness and surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If sawing processes are used to separate thin substrates from substrate blocks, then separation can be achieved, but material loss in the kerf volume is disproportionately high (up to 150 μm) compared to component thickness
Solution Approach 1:
The patent replaces mechanical sawing processes with a laser-based method. Focused laser pulses create subsurface modifications and stress zones that enable fracture separation without mechanical contact, eliminating the kerf width problem inherent in mechanical sawing and achieving near-net-shape separation with minimal material loss.
Solution Approach 2:
The laser process performs preliminary action by creating subsurface modifications, stress zones, and pre-fracture paths before the actual separation occurs. This preliminary laser-induced preparation enables subsequent fracture to proceed along predetermined paths with high precision and minimal material removal.
2Manufacturing precision
If conventional laser ablation methods are used, then material can be removed, but the laser beams are focused onto the surface causing excessive material removal and poor contour accuracy
Solution Approach 1:
The patent transitions from surface-focused laser ablation to subsurface-focused laser processing. By focusing laser beams at depths below the surface (e.g., 10-100 μm), the method creates modifications in the subsurface region rather than removing surface material, enabling precise fracture path definition with minimal material loss and excellent contour accuracy.
Solution Approach 2:
The laser performs preliminary action by creating subsurface modifications, stress zones, and pre-fracture paths before actual separation. This preliminary preparation at subsurface depths enables subsequent fracture to occur along predetermined paths without requiring excessive material removal.
3Productivity
If wire sawing processes are used for separating substrates, then separation can be achieved, but cutting speeds are limited to up to 6 mm/min resulting in long processing times
Solution Approach 1:
The patent replaces mechanical wire sawing with a laser-based fracture method. The laser creates subsurface modifications and stress zones that enable rapid fracture separation, achieving cutting speeds significantly higher than mechanical sawing (e.g., >6 mm/min) while maintaining or improving separation quality through precise laser control.
Solution Approach 2:
The laser operates in pulsed mode, delivering periodic energy bursts to create subsurface modifications along the fracture path. This periodic laser action enables rapid processing speeds while maintaining precision through controlled pulse timing and energy delivery.
4Ease of manufacture
If diamond-coated wires or diamond-tipped saw blades are used, then separation can be achieved, but tooling costs are high due to diamond consumption
Solution Approach 1:
The patent replaces diamond-based mechanical cutting tools with a laser-based fracture method. This substitution eliminates the need for expensive diamond-coated wires or diamond-tipped blades, significantly reducing tooling costs while maintaining separation capability through optical field interaction with the material.
Solution Approach 2:
The laser method replaces expensive, consumable diamond tools with a non-contact optical process. The laser system has no physical contact with the workpiece, eliminating tool wear and the need for expensive replacement tools, thereby reducing operational costs and improving ease of manufacture.
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 method achieves significant reductions in material loss and processing time, enabling the production of substrates with Total Thickness Variation (TTV) less than 50 μm and surface roughness better than 0.6 μm, with cutting speeds up to 250 mm/s, and eliminates the need for extensive polishing, resulting in cost-effective and high-accuracy thin substrates.
Implementation Method 1
the fracture surface is produced by repeatedly perforating the substrate block at least partially along at least one desired fracture surface by means of focused laser pulses
Implementation Method 2
the laser beams are not focused onto the surface of the material, but rather concentrated within the substrate. Particularly when the laser is pulsed, this leads to filament formation within the substrate. Focusing the laser within the material causes local vaporization
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4B
AI summary
The invention relates to a method for producing thin substrates. The invention particularly relates to a laser-based method for separating thin substrates from a substrate block.