AlGaN Nitride Substrate Regrowth Using a Porous Intermediate Layer
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Solution Overview
Problem
Existing methods for producing nitride crystal substrates, particularly AlGaN substrates, face challenges due to lattice mismatch, which leads to crystal strain and cracks, making it difficult to achieve high-quality devices.
Innovation Solution
A production method involving the preparation of a base substrate, formation of an intermediate and cover layer, making the intermediate layer porous through dislocations in the cover layer using an electrochemical process, and epitaxially growing a regrowth layer on the cover layer, which is then peeled off using the porous intermediate layer as a boundary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing methods are used to produce AlGaN nitride crystal substrates, then production can be achieved, but lattice mismatch causes crystal strain and cracks, reducing substrate quality
Solution Approach 1:
The patent introduces an intermediate layer between the base substrate and the AlGaN regrowth layer. This intermediate layer acts as a mediator that accommodates lattice mismatch, preventing crystal strain and cracks from propagating through the structure. The intermediate layer absorbs the dimensional discrepancy between the base substrate and the AlGaN crystal, enabling high-quality substrate production without compromising crystal integrity.
Solution Approach 2:
The patent employs an electrochemical process to modify the intermediate layer, making it porous. This parameter change in the intermediate layer's structure (from dense to porous) allows for stress relief and accommodation of lattice mismatch. The porosity parameter is specifically controlled to maintain electrical insulation while providing mechanical compliance, thereby resolving the contradiction between manufacturing precision and reliability.
2Ease of manufacture
If lattice mismatch is present during AlGaN growth, then crystal strain occurs, but this leads to cracks and defects in the substrate
Solution Approach 1:
The intermediate layer serves as a buffer that mediates the lattice mismatch between the base substrate and the AlGaN regrowth layer. By placing this intermediary layer, the patent enables the AlGaN growth process to proceed without the harmful effects of direct lattice contact, thus maintaining ease of manufacture while significantly reducing crystal defects.
Solution Approach 2:
The patent transforms the intermediate layer into a porous material through electrochemical processing. This porous structure provides mechanical compliance and stress relief, allowing the AlGaN layer to grow with reduced strain accumulation. The controlled porosity enables the material to accommodate lattice differences without forming cracks, thereby improving manufacturing precision while maintaining growth feasibility.
3Manufacturing precision
If the intermediate layer is made porous to reduce strain, then crystal quality improves, but the layer loses structural integrity
Solution Approach 1:
The patent deliberately creates a porous intermediate layer to improve crystal quality by reducing strain. The porosity is carefully controlled to provide sufficient stress relief while maintaining adequate structural integrity. The porous structure allows the layer to function as a compliant buffer without completely sacrificing its mechanical strength, resolving the contradiction between crystal quality and layer strength.
Solution Approach 2:
The intermediate layer can be viewed as a composite structure with both solid and void phases. This composite nature allows the layer to exhibit both mechanical strength from the solid framework and strain accommodation from the porous structure. The composite design enables simultaneous achievement of crystal quality improvement and sufficient layer strength.
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 allows for the stable production of nitride crystal substrates with AlGaN, reducing crystal strain and eliminating cracks, thereby enabling the growth of high-quality AlGaN crystal substrates without defects.
Implementation Method 1
making the intermediate layer porous through dislocations in the cover layer by performing an electrochemical process
Implementation Method 2
epitaxially growing a regrowth layer comprising group III nitride crystal, on the cover layer
Data Source
AI summary
To stably obtain a nitride crystal substrate containing AlGaN. A production method for a nitride crystal substrate includes: (a) preparing a base substrate; (b) forming an intermediate layer including n-type group III nitride crystal, above the base substrate; (c) forming a cover layer on the intermediate layer, the cover layer including group III nitride crystal having a carrier concentration lower than a carrier concentration of the intermediate layer; (d) making the intermediate layer porous through dislocations in the cover layer by performing an electrochemical process, while maintaining a surface condition of the cover layer; (e) epitaxially growing a regrowth layer comprising group III nitride crystal, on the cover layer; and (f) peeling off the regrowth layer from the base substrate by using at least a portion of the intermediate layer made porous as a boundary, wherein in (e), crystal represented by a composition formula of AlxGa1-xN, where an Al composition ratio x is 0.05 or more and 0.8 or less, is grown as the regrowth layer.