Laser Modification Spacing for Short Subcritical Cracks in Crystals
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Solution Overview
Problem
Existing methods for producing modifications in solid bodies, such as silicon carbide wafers, result in uncontrollable material transformation and extensive crack propagation due to close focal points, leading to significant damage and increased reworking efforts.
Innovation Solution
A method involving precise laser radiation with controlled focal point spacing and polarization to create subcritical cracks, limiting crack propagation and reducing material transformation effects, allowing for controlled material separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If focal points are placed close together to increase productivity, then processing speed improves, but uncontrolled material transformation and extensive crack propagation occur
Solution Approach 1:
The patent applies parameter changes by carefully controlling the spacing between focal points (maintaining distance > d) and adjusting laser pulse duration (50ps-4000ps) to achieve subcritical crack formation without uncontrolled material transformation. This resolves the contradiction by finding optimal parameter values that maintain both productivity and material integrity.
Solution Approach 2:
The patent uses partial action by delivering laser energy in controlled pulses rather than continuous irradiation. Each pulse creates a modification zone, and by controlling pulse frequency and spacing, the process achieves productive crack formation without excessive energy input that would cause uncontrolled transformation.
2Loss of time
If focal points are placed close together to reduce processing time, then efficiency improves, but extensive crack propagation and material damage increase
Solution Approach 1:
The patent changes the parameter of focal point spacing to be greater than the focal point diameter (d), which prevents crack propagation while maintaining efficient processing. Additionally, controlling pulse duration within 50ps-4000ps range ensures cracks remain subcritical and confined, resolving the time-quality contradiction.
Solution Approach 2:
The patent segments the laser processing into discrete pulses with controlled spacing, where each pulse creates an isolated modification zone. This segmentation prevents crack propagation between zones, allowing fast processing without extensive damage.
3Length of stationary object
If more material is transformed to create deeper modifications, then penetration depth improves, but greater compressive stresses and crack propagation occur
Solution Approach 1:
The patent uses periodic laser pulsing with controlled duration (50ps-4000ps) and spacing to progressively create modifications at different depths. This periodic action allows controlled energy deposition that achieves penetration depth while preventing excessive stress accumulation through proper timing and spacing.
Solution Approach 2:
The patent changes multiple parameters including pulse duration, pulse spacing (>d), and focal point positioning to achieve the desired penetration depth while maintaining compressive stresses within acceptable limits. By adjusting these parameters, deep modifications are created without triggering extensive crack propagation.
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 less damage to the solid body by producing subcritical cracks with controlled crack lengths and orientations, reducing the need for extensive reworking and improving the efficiency of material separation.
Implementation Method 1
laser radiation of a laser is introduced into the interior of the solid body via a first surface of the solid body
Implementation Method 2
producing a multiplicity of modifications by means of multiphoton excitation
Implementation Method 3
The solid body cracks subcritically in the region of the respective modification
Data Source
AI summary
The invention relates to a method for producing modifications (9) in the interior of a solid body (1). The method comprises the introduction of laser radiation (14) of a laser (29) into the interior of the solid body (1) via a first surface (8) of the solid body (1). The solid body (1) forms a crystal structure. Modifications (9) are produced at predefined points in a production plane (4) in the interior of the solid body (1) by the laser radiation (14). The modifications (9) are closer to the first surface (8) than to a second surface, the second surface being parallel to the first surface (8). A plurality of linear forms (103) can be produced by the modifications (9). The solid body (1) cracks subcritically in the region of each modification (9). The subcritical cracks have an average crack length of less than 150 μm orthogonally to the direction of longitudinal extent of the linear form in question. Modifications (9) that belong to the same linear form (103) and that are produced one after the other are produced at a distance from each other that is defined by the function (d−x)/d<−0.31, where x>d.