Donor Substrate Edge Cracking With Angled Laser Wafer Separation
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Solution Overview
Problem
Conventional methods for producing wafers result in significant material loss and thickness variations, making them unsuitable for many applications due to high total thickness variation (TTV) and crack formation issues, especially at the edges where laser beams struggle to create precise cracks.
Innovation Solution
A method involving LASER beams that penetrate the donor substrate at angled planes to produce modifications, with thermal treatment inducing mechanical stresses for crack propagation, allowing for homogeneous damage and precise crack formation across the wafer, including the edges, using a stress-inducing layer and controlled indentation to minimize material loss and TTV.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a LASER beam is used to produce modifications in the edge region of the donor substrate, then crack formation should be enabled, but edge effects cause damaged sides beyond the intended damage layer and reduced damage
Solution Approach 1:
The patent applies asymmetry by using different LASER beam angles for edge regions compared to central regions. Specifically, the beam angle is adjusted to account for the asymmetric geometry at the edge, where one side of the beam would otherwise fall into air rather than material. This asymmetric adjustment ensures that the modification depth and damage distribution are homogeneous across the entire donor substrate, including edges.
Solution Approach 2:
The patent changes the LASER beam parameter (angle of incidence) depending on the position on the donor substrate. For central regions, a standard angle is used, while for edge regions, the angle is modified to compensate for edge effects. This parameter adaptation ensures that the modification depth remains consistent throughout the substrate, achieving homogeneous damage distribution and enabling precise crack formation even at edges.
2Productivity
If conventional sawing methods are used to produce wafers, then material can be separated, but significant material loss occurs as kerf loss
Solution Approach 1:
The patent replaces the mechanical sawing system with a LASER-based modification system. Instead of using a physical saw blade that removes material as kerf, the invention uses LASER beams to create modifications within the donor substrate that enable crack propagation along desired paths. This substitution eliminates the need for material removal, achieving kerf-free wafering and significantly reducing material loss while maintaining high production efficiency.
Solution Approach 2:
The patent utilizes phase transitions in the donor substrate material induced by LASER heating. The LASER beam creates localized thermal fields that cause phase changes (melting, vaporization, or structural transformation) along the intended crack path. These phase transitions create the necessary modifications and stress concentrations that guide crack propagation, enabling precise wafer separation without mechanical contact or material removal.
3Loss of substance
If polymer layers are used to produce temperature-induced stresses for kerf-free wafering, then material loss is reduced, but the produced wafers exhibit high thickness variations with tetramerous symmetry patterns
Solution Approach 1:
The patent extracts or removes the polymer layer from the process, replacing it with direct LASER beam application. By eliminating the polymer layer, the source of tetramerous thickness variation patterns is removed. The LASER beam directly creates modifications in the donor substrate without introducing the stress distribution patterns that arise from polymer layer thermal expansion and contraction, thereby achieving both kerf-free separation and homogeneous thickness distribution.
Solution Approach 2:
The patent introduces a different intermediary mechanism - using LASER-induced modifications as the mediating structure for crack propagation, rather than relying on polymer layer stress fields. These LASER-created modifications serve as controlled weak points that guide crack paths without imposing the tetramerous stress patterns that polymer layers inherently create, thus achieving uniform thickness distribution while maintaining the kerf-free advantage.
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 wafers with low TTV and reduced material loss, enabling more efficient and cost-effective production by ensuring homogeneous damage and precise crack formation, suitable for various applications without the disruptions caused by high TTV and edge-related issues.
Implementation Method 1
producing at least one modification within the donor substrate by means of at least one LASER beam, wherein the LASER beam penetrates the donor substrate via a planar surface of the donor substrate
Implementation Method 2
a stress-inducing layer is produced or arranged on the planar surface of the donor substrate and mechanical stresses are produced in the donor substrate by a thermal treatment of the stress-inducing layer
Implementation Method 3
the LASER beam is focused in order to produce the modification in the donor substrate
Implementation Method 4
mechanical stresses are produced in the donor substrate by a thermal treatment of the stress-inducing layer, wherein the mechanical stresses produce a crack for separating a solid-body layer
Data Source
AI summary
A method for separating a solid-body layer from a donor substrate includes providing a donor substrate having a planar surface, a longitudinal axis orthogonal to the planar surface, and a peripheral surface, and producing modifications within the donor substrate using at least one LASER beam. The at least one LASER beam penetrates the donor substrate via the peripheral surface at an angle not equal to 90° relative to the longitudinal axis of the donor substrate. The method further includes producing a stress-inducing polymer layer on the planar surface of the donor substrate, and producing mechanical stresses in the donor substrate by a thermal treatment of the stress-inducing polymer layer. The mechanical stresses produce a crack for separating the solid-body layer, and wherein the crack propagates along the modifications.