Group-III Nitride Crystal Surface Flatness Improvement
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Solution Overview
Problem
Group-III nitride crystals used in semiconductor devices face challenges with surface flatness and dislocation density due to lattice mismatch, which affect device performance, and existing techniques do not adequately address these issues.
Innovation Solution
A substrate for epitaxial growth involving a single crystal base with a group-III nitride crystal upper layer undergoes a heating process at temperatures above the formation temperature, specifically at least 1500°C, to improve surface flatness and reduce dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a group-III nitride crystal is epitaxially formed on a single crystal base, then the crystal can be grown with controlled thickness, but lattice mismatch causes dislocations that propagate to the surface and degrade device performance
Solution Approach 1:
The crystal structure is segmented into multiple layers: a base layer, an intermediate group-III nitride layer with specific thickness (0.5-5 μm), and an upper group-III nitride crystal layer. This segmentation allows the intermediate layer to absorb dislocations while maintaining controlled thickness for the functional crystal layer, thus resolving the contradiction between thickness control and device performance.
Solution Approach 2:
An intermediate group-III nitride crystal layer is introduced as a mediator between the single crystal base and the upper functional crystal layer. This intermediate layer acts as a buffer that absorbs lattice mismatch dislocations, preventing them from propagating to the surface and degrading device performance, while still allowing controlled growth of the upper layer.
2Reliability
If the upper layer thickness is increased to improve crystal quality, then dislocation density may be reduced, but surface flatness deteriorates due to pit formation
Solution Approach 1:
The thickness of the intermediate group-III nitride layer is optimized to a specific range (0.5-5 μm). This parameter optimization allows the layer to be thick enough to absorb dislocations and improve crystal quality, yet thin enough to maintain surface flatness and prevent pit formation, thus resolving the contradiction between crystal quality and surface flatness.
3Manufacturing precision
If a heating process is applied to improve surface flatness, then pits are eliminated and surface roughness improves, but the process temperature must be precisely controlled above formation temperature
Solution Approach 1:
A heating process is applied after the upper layer is formed to pre-treat the surface before final device fabrication. This preliminary heating action eliminates pits and improves surface roughness by facilitating material redistribution, thereby improving surface flatness without requiring complex in-situ control during crystal growth.
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 effectively eliminates pits and improves surface roughness, reducing dislocation density and enhancing crystal quality, leading to better device performance such as increased light emitting efficiency and reduced dark current.
Implementation Method 1
the substrate for epitaxial growth being subjected to a heating process after the formation of the upper layer, the heating process being performed at a heating temperature higher than a temperature at which the group-III nitride crystal is formed
Implementation Method 2
This method effectively eliminates pits and improves surface roughness, reducing dislocation density and enhancing crystal quality
Data Source
AI summary
A heating process is performed in a nitrogen atmosphere at a temperature of not less than 1650° C. upon an epitaxial substrate including a single crystal base and an upper layer made of a group-III nitride crystal and epitaxially formed on a main surface of the single crystal base. The result shows that the heating process reduces the number of pits in a top surface to produce the effect of improving the surface flatness of the group-III nitride crystal. The result also shows that the dislocation density in the group-III nitride crystal is reduced to not more than one-half the dislocation density obtained before the heat treatment.