Epitaxial Structure with Pattern Mask Layers for GaN Buffer
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Solution Overview
Problem
Conventional gallium nitride semiconductor manufacturing processes face issues with misfit dislocations and thermal stress due to lattice constant and thermal expansion coefficient mismatches between semiconductor layers and hetero-substrates, leading to defects and increased chances of cracking in epitaxial structures.
Innovation Solution
The epitaxial structure incorporates alternately stacked buffer layers and pattern mask layers on an epitaxial substrate, with the pattern mask layers covering at least 70% of the buffer layers' area to block misfit dislocations, thereby preventing their extension and improving the epitaxial quality of subsequently stacked semiconductor layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional epitaxial growth is performed directly on hetero-substrate, then manufacturing process is simple, but misfit dislocations and thermal stress cause severe bending and cracking
Solution Approach 1:
The patent divides the epitaxial structure into multiple segments: hetero-substrate, nucleating layer, first buffer layer, second buffer layer, and semiconductor layer. Each layer serves as a separate stage to gradually transition from the substrate to the final semiconductor layer, reducing stress and dislocation propagation through incremental lattice matching.
Solution Approach 2:
The nucleating layer and buffer layers are formed in advance before growing the semiconductor layer. These preliminary layers prepare the substrate surface and create a graded lattice structure that prevents misfit dislocations from propagating to the semiconductor layer, ensuring better crystal quality beforehand.
2Ease of manufacture
If buffer layers are grown without pattern mask layers, then epitaxial growth is straightforward, but misfit dislocations extend upward causing defects
Solution Approach 1:
Pattern mask layers are selectively positioned at specific locations within the buffer layers to block misfit dislocations only where they would otherwise propagate upward. This localized intervention prevents defects in critical areas while maintaining overall process efficiency.
Solution Approach 2:
Pattern mask layers act as intermediary elements between the buffer layers and the semiconductor layer. These mask layers intercept and block misfit dislocations, preventing them from reaching the semiconductor layer and causing defects, thus mediating the stress and dislocation flow.
3Reliability
If pattern mask layers cover entire buffer layer area, then misfit dislocation blocking is maximized, but manufacturing complexity and process steps increase
Solution Approach 1:
Pattern mask layers cover only portions of the buffer layers rather than the entire area. This partial coverage is sufficient to block the critical paths of misfit dislocation propagation while avoiding the unnecessary complexity of complete area coverage, achieving optimal defect prevention with reduced process complexity.
Data Source
AI summary
An epitaxial structure including an epitaxial substrate, a first buffer layer, a first pattern mask layer, a second buffer layer and a second pattern mask layer. The first buffer layer is disposed on the epitaxial substrate. The first pattern mask layer is disposed on the first buffer layer. The second buffer layer is disposed on the first pattern mask layer and a part of the first buffer layer. The second pattern mask layer is disposed on the second buffer layer. A projection of the first pattern mask layer projected on the first buffer layer and a projection of the second pattern mask layer projected on the first buffer layer cover at least 70% of the total area of the first buffer layer.