III-Nitride Ingot Cracking via Edge Etching
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Solution Overview
Problem
The challenge in growing longer III-nitride monocrystal ingots is the occurrence of cracking due to thermal stress discrepancies between monocrystal and polycrystal or out-of-plane oriented crystal deposits on the periphery, which is exacerbated by the anisotropic thermal expansion coefficients of III-nitride crystals.
Innovation Solution
The method involves etching the edge surface of a base substrate to form crystallographic planes on the side surfaces of the ingot, controlling the deposition of polycrystal and out-of-plane oriented crystal, and creating regions with varying oxygen-impurity concentrations to minimize cracking during length-extending growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If III-nitride monocrystal is grown under conventional conditions, then crystal growth can proceed, but cracking occurs during growth due to thermal stress discrepancies between monocrystal and polycrystal deposits
Solution Approach 1:
The base substrate undergoes preliminary etching treatment before crystal growth to create specific surface conditions. This preliminary action removes mechanical alterations and creates a controlled surface state that prevents polycrystal and out-of-plane oriented crystal deposition during subsequent growth, thereby eliminating thermal stress discrepancies and cracking while enabling extended ingot growth
Solution Approach 2:
The invention applies different treatments to different regions of the base substrate. The edge surfaces are etched to create specific crystallographic planes, while the central region maintains different properties. This local differentiation ensures that the edge surfaces specifically prevent polycrystal deposition without affecting the overall growth process, resolving the cracking issue while maintaining productivity
2Reliability
If polycrystal and out-of-plane oriented crystal deposit onto the periphery of the monocrystal, then gas-flow variation and crystal-quality loss are reduced, but thermal stress discrepancy increases causing cracks
Solution Approach 1:
The invention converts the potentially harmful effect of gas-flow variation and crystal-quality loss at the margins into a beneficial outcome. By etching the edge surfaces to create specific crystallographic planes, the invention directs the deposition process to form controlled crystal structures on the edges, transforming what would be harmful polycrystal deposition into beneficial controlled crystal growth that eliminates thermal stress discrepancies
Solution Approach 2:
The invention changes the surface parameters of the base substrate by etching the edge surfaces to create specific crystallographic planes. This parameter change modifies the deposition behavior of subsequent crystals, ensuring that only properly oriented crystal grows on the edges, thereby eliminating thermal stress discrepancies while maintaining crystal quality uniformity
3Ease of manufacture
If the base substrate edge surface is not etched, then manufacturing process is simpler, but polycrystal and out-of-plane oriented crystal deposit onto the periphery causing thermal stress and cracking
Solution Approach 1:
The etching of the base substrate edge surface is performed as a preliminary action before the main crystal growth process. This preliminary step, while adding a bit of process complexity, prevents subsequent polycrystal deposition and cracking, thereby ensuring reliable crack-free growth and extended ingot length
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 approach effectively reduces the incidence of cracking in III-nitride single-crystal ingots, enabling the efficient manufacture of substrates with reduced defects and extended growth lengths.
Implementation Method 1
a step of etching the edge surface of a base substrate
Implementation Method 2
a step of epitaxially growing onto the base substrate hexagonal-system III-nitride monocrystal having crystallographic planes on its side surfaces
Implementation Method 3
In the case of GaN crystal, for example, the a-plane thermal expansion coefficient is 5.59×10−6/° C., whereas the c-plane thermal expansion coefficient is 3.17×106−/° C. Consequently, during growth of III-nitride monocrystal, in cases where polycrystal and out-of-plane oriented crystal has deposited onto the periphery of the monocrystal, a thermal stress discrepancy, deriving from the difference in thermal expansion coefficient, develops
Data Source
AI summary
Affords Group-III nitride single-crystal ingots and III-nitride single-crystal substrates manufactured utilizing the ingots, as well as methods of manufacturing III-nitride single-crystal ingots and methods of manufacturing III-nitride single-crystal substrates, wherein the incidence of cracking during length-extending growth is reduced. Characterized by including a step of etching the edge surface of a base substrate, and a step of epitaxially growing onto the base substrate hexagonal-system III-nitride monocrystal having crystallographic planes on its side surfaces. In order to reduce occurrences of cracking during length-extending growth of the ingot, depositing-out of polycrystal and out-of-plane oriented crystal onto the periphery of the monocrystal must be controlled. A layer of the base substrate edge surface, as just described, where it has been mechanically altered is removed beforehand by etching, whereby crystallographic planes form on the side surfaces of the III-nitride single-crystal ingot that is formed onto the base substrate, which therefore controls depositing-out of polycrystal and out-of-plane oriented crystal and reduces occurrences of cracking.