Wafer Separation with Oriented Laser Modification and Subcritical Cracks
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Solution Overview
Problem
Traditional wafering methods for semiconductor materials result in material loss, surface roughness, and subsurface damage due to diamond or slurry-based wire sawing, and existing kerf-less technologies like spalling have limitations in controlling wafer thickness and surface roughness, leading to increased surface roughness and material loss.
Innovation Solution
A method involving a donor substrate with inclined crystal lattice planes, where laser radiation is used to create subcritical cracks by changing material properties, allowing for controlled separation of solid layers with reduced material loss and surface roughness by aligning the linear shape of material modification parallel to the substrate surface, limiting crack propagation along crystal lattice planes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If diamond or slurry-based wire sawing processes are used for wafering, then material can be separated from the ingot, but material loss occurs due to kerf and surface roughness and subsurface damage are caused
Solution Approach 1:
The patent replaces mechanical sawing processes with a laser-based modification system. Laser radiation is introduced into the interior of the solid via the main surface to modify material properties and create subcritical cracks, which then propagate to separate the wafer. This substitution eliminates mechanical contact that causes kerf loss and surface damage, achieving kerf-less separation while maintaining precise thickness control through the inclined crystal lattice plane geometry
Solution Approach 2:
The patent applies preliminary laser-induced modifications to create subcritical cracks and alter material properties before the actual separation occurs. By pre-modifying the material along the desired separation plane using laser radiation, the subsequent separation process proceeds without mechanical force, preventing surface roughness and subsurface damage that would otherwise require additional polishing steps
2Loss of substance
If spalling is used for kerf-free wafering, then material loss is reduced, but Wallner lines with increased surface roughness are produced
Solution Approach 1:
The patent applies local quality by directing laser radiation specifically along the inclined crystal lattice planes to create modifications and subcritical cracks only where needed for separation. The laser focus is positioned at a specific depth corresponding to the desired wafer thickness, and the linear shape of modifications is oriented at an angle to the crystal lattice planes. This localized modification approach separates the wafer without producing Wallner lines, as the crack propagation is guided by the laser-modified regions rather than uncontrolled stress fields
Solution Approach 2:
The patent changes the parameters of the separation process by using laser-induced subcritical cracks instead of conventional stress-based spalling. The laser radiation modifies material properties (absorption, refractive index) at the focus region, creating a controlled crack initiation zone. By adjusting laser parameters (energy, duration, position) and the inclination angle of the linear shape relative to crystal lattice planes, the process achieves clean separation without the harmful Wallner line patterns associated with traditional spalling
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 significantly reduces material loss and surface roughness, enabling more efficient production of electrical components with fewer additional polishing or grinding steps, and allows for precise control over wafer thickness and surface quality.
Implementation Method 1
introducing laser radiation from a laser into the interior of the solid via the main surface to modify the material properties of the solid in the region of at least one laser focus
Implementation Method 2
The donor substrate cracks in the form of subcritical cracks due to the changed material properties
Data Source
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AI summary
The present invention therefore relates to a method for separating at least one solid body layer (2) from a donor substrate (1). According to the invention, the method preferably comprises at least the steps of: providing the donor substrate (1), wherein the donor substrate (1) has crystal lattice planes (6) which are inclined in relation to a planar main surface (8), wherein the main surface (8) delimits the donor substrate (1) in the longitudinal direction of the donor substrate (1) on one side, wherein a crystal lattice plane normal is inclined in relation to a main surface normal in a first direction, providing at least one laser, introducing laser radiation of the laser into the interior of the donor substrate (1) via the main surface (8) for changing the material properties of the donor substrate (1) in the region of at least one laser focus, wherein the laser focus is formed by laser beams of the laser which are emitted by the laser, wherein the change in the material property by changing the point of entry of the laser radiation into the donor substrate (1) forms a linear shape (103), wherein the changes in the material property are generated on at least one generating plane (4), wherein the crystal lattice planes (6) of the donor substrate (1) are oriented in an inclined manner in relation to the generating plane (4), wherein the linear design (103) is inclined in relation to a sectional line (10) which is produced at the interface between the generating plane (4) and the crystal lattice plane (6), wherein, owing to the changed material property, the donor substrate (1) tears in the form of subcritical cracks, separating the solid body layer (2) by introducing an external force into the donor substrate (1) for connecting the subcritical crack or so much material on the generating plane (4) being changed by means of the laser radiation that the solid body layer (2) becomes detached from the donor substrate (1) with connection of the subcritical crack.