GaN Substrate Dislocation Reduction via Na Melt Etching
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Solution Overview
Problem
Conventional methods for producing GaN crystals, such as the flux method, result in high dislocation densities, typically in the range of 5×10^5 to 1×10^7/cm², which is undesirable for semiconductor applications, as lower dislocation densities are preferred for improved crystallinity and device performance.
Innovation Solution
A method involving the formation of a protective film on the N polarity surface of a Group III nitride semiconductor, followed by etching the Ga polarity surface in a melt containing sodium, with a mask layer of AlXInYGa(1-X-Y)N and a temperature range of 600° C to 1000° C, to create deep concave portions that reduce dislocation inheritance during crystal growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the flux method is used to grow GaN crystals at low temperature and pressure, then production cost is reduced and growth conditions are simplified, but dislocation density increases to 5×10^6/cm² to 1×10^7/cm²
Solution Approach 1:
The patent applies preliminary action by forming a protective film on the N-polarity surface before the flux method growth process. This protective film prevents dislocation inheritance from the underlayer to the GaN crystal, thereby reducing dislocation density while maintaining the cost-effective flux method growth conditions.
Solution Approach 2:
The protective film acts as an intermediary layer between the underlayer and the GaN crystal. It mediates the growth process by blocking dislocation propagation while allowing the flux method to proceed, thus resolving the contradiction between ease of manufacture and manufacturing precision.
2Manufacturing precision
If a mask layer is formed on a seed crystal and GaN is laterally grown over the mask, then dislocation density is reduced, but the process complexity increases
Solution Approach 1:
The patent extracts the protective function from the complex mask layer structure and implements it as a simple protective film formed on the N-polarity surface. This extraction simplifies the process while maintaining the dislocation reduction effect, resolving the contradiction between manufacturing precision and device complexity.
3Productivity
If the N polarity surface is etched in Na melt, then etching proceeds effectively, but the first surface cannot be protected from etching
Solution Approach 1:
The patent applies local quality by making the N-polarity surface different from the Ga-polarity surface through protective film formation. The N-polarity surface receives protective film treatment while the Ga-polarity surface does not, creating local differentiation that enables selective etching and achieves both etching efficiency and surface selectivity.
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 enables the formation of GaN crystals with significantly reduced dislocation density, achieving excellent crystallinity and allowing for the stable growth of GaN substrates with dislocation densities of 1×10^5/cm² or less, thereby improving semiconductor quality.
Implementation Method 1
a protective film formation step of forming a protective film on a first surface being a N polarity surface of Group III nitride semiconductor
Implementation Method 2
an etching step of etching at least a portion of a second surface of Group III nitride semiconductor in a melt containing at least Na
Data Source
AI summary
A mask layer is formed on a Ga polarity surface of the GaN substrate as a growth substrate. Subsequently, a protective film PF is formed on a N polarity surface of the GaN substrate. Then, a plurality of concave portions is formed from the mask layer extending to the GaN substrate, to thereby form a seed crystal. The seed crystal is etched in a Na melt, and a plurality of concave portions having a facet plane exposed. The seed crystal and the raw materials are placed in a crucible, and the pressure and temperature inside the crucible are increased. Thus, a target GaN layer is grown in the upward direction on the surface of the mask layer and the lateral direction over the concave portions.