Epitaxial Substrate Dislocation Reduction via Thermal Step Flow
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Solution Overview
Problem
Current methods for forming group III nitride crystals on epitaxial substrates face challenges such as lattice mismatch-induced dislocations, high manufacturing costs, and surface defects, which affect the crystal quality and device performance, particularly in light-emitting and electronic devices.
Innovation Solution
An epitaxial substrate with an Al content of not less than 80 mole percent is formed on a base with an off-angle, followed by a heating process at temperatures above 1500°C to create periodic steps on the surface, reducing dislocations and improving crystal quality, allowing for the growth of group III nitride crystals with excellent surface flatness and reduced dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a group-III nitride crystal is formed on a base for device function, then device performance is improved, but dislocation density increases due to lattice mismatch
Solution Approach 1:
The patent introduces an AlN upper layer as an intermediary between the base and the device functional layer. This intermediate layer serves as a buffer that reduces the lattice mismatch stress, preventing dislocation propagation to the device layer while maintaining device performance
Solution Approach 2:
The patent performs preliminary actions by forming the AlN upper layer with specific thickness (not less than 10 nm) and performing heating treatment before device fabrication. These preliminary steps prepare the substrate by reducing dislocation density and improving crystal quality in advance, preventing harmful effects during subsequent device manufacturing
2Manufacturing precision
If epitaxial lateral overgrowth technique is used to reduce dislocation density, then crystal quality is improved, but manufacturing complexity increases due to mask formation step
Solution Approach 1:
The patent extracts and eliminates the mask formation step from the ELO process by using a different approach - forming a thick AlN upper layer followed by heating treatment. This removes the complex mask fabrication and alignment steps while achieving similar or better dislocation reduction through thermal treatment-induced crystal restructuring
Solution Approach 2:
The patent replaces the mechanical mask-based lateral overgrowth method with a thermal field-based approach. By applying heating treatment to the AlN layer, the crystal structure reorganizes and dislocations are reduced through thermally activated processes, substituting mechanical patterning with thermal field control
3Manufacturing precision
If a larger step is provided to the underlayer to improve crystalline quality, then crystal quality is improved, but surface flatness deteriorates due to step propagation
Solution Approach 1:
The patent changes the parameter of AlN layer thickness to not less than 10 nm and applies heating treatment at specific temperature ranges. These parameter changes enable the AlN layer to undergo structural reorganization that reduces dislocations without propagating surface steps, achieving both crystal quality improvement and surface flatness maintenance
Solution Approach 2:
The heating treatment induces phase transitions or structural transformations in the AlN layer, allowing the crystal structure to reorganize and eliminate dislocations. This thermal activation enables the material to transition from a high-dislocation state to a low-dislocation state while maintaining surface integrity
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 results in group III nitride crystals with significantly reduced dislocation density and improved surface flatness, enhancing the performance of semiconductor devices by minimizing defects and maintaining transparency across short wavelength ranges.
Implementation Method 1
a heating process is performed at temperatures above 1500°C to create periodic steps on the surface, reducing dislocations and improving crystal quality
Implementation Method 2
a group III nitride crystal layer is grown from points of the steps
Implementation Method 3
a group-III nitride crystal is typically provided in the form of a so-called epitaxial substrate such that the group-III nitride crystal having a thickness of the order, at most, of 10 μm is epitaxially formed on a predetermined single crystal base
Data Source
Figure 1~2
Figure 3A~3D
AI summary
The present invention provides an epitaxial substrate which is appropriate for the generation of a group III nitride crystal having excellent crystal quality. An upper layer 2 of a group III nitride is formed on a sapphire base with an off angle, and after that a heating process is performed at a temperature not lower than 1500°C, preferably not lower than 1650°C, and thereby, the crystal quality of the upper layer 2 is improved and repeating steps of which the size is greater than the height of several atomic layers are provided on the surface of the upper layer 2, and thus obtained epitaxial substrate 10 is used as a base substrate for growing a group III nitride crystal layer 3. The group III nitride crystal grows from the points of steps in a manner of step flow, and therefore, threading dislocations from the upper layer 2 are bent according to this growth, and are unevenly distributed as the crystal grows afterwards. The obtained group III nitride crystal layer 3 has an excellent surface flatness, and most portions in the vicinity of the surface become low dislocation regions where the density of dislocations is approximately 1 × 107/cm2. That is, it can be said that the epitaxial substrate 10 is appropriate for the formation of a group III nitride crystal having excellent crystal quality.