Composite Semiconductor Substrate Managing Lattice Mismatch and Warpage
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Solution Overview
Problem
The production of GaN semiconductor devices using an Si substrate often results in warpage and cracks due to lattice constant and thermal expansion coefficient differences, and doping with carbon to improve tolerance degrades the crystalline quality of nitride semiconductor layers.
Innovation Solution
A composite semiconductor substrate is developed with an Si or SOI substrate, an SiC layer, and multiple AlInGaN layers, where the average density of C and Fe in certain layers is higher than in others, and the compositional ratios of Al, In, and Ga vary across layers to enhance voltage withstanding and crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an Si substrate is used as a foundation substrate for growing GaN, then the manufacturing cost is reduced and large diameter substrates can be produced, but warpage of the substrate and cracks in the GaN layer occur due to large differences in lattice constants and thermal expansion coefficients
Solution Approach 1:
The buffer layer is segmented into multiple sub-layers with different compositions (AlN, AlGaN, AlInGaN layers with varying Al and In contents). Each sub-layer has a specific function in managing lattice mismatch and thermal stress, allowing the structure to accommodate the large differences between Si and GaN while maintaining structural integrity and preventing warpage and cracks.
Solution Approach 2:
Different regions of the buffer layer have different compositional qualities. The AlN layer provides strong lattice matching, while AlGaN and AlInGaN layers provide gradient transition and stress management. This local variation in material composition optimizes both the mechanical reliability and the manufacturing feasibility of the GaN-on-Si structure.
2Reliability
If carbon doping is applied to improve tolerance of nitride semiconductor layers, then the voltage withstanding is improved, but the crystalline quality of the nitride semiconductor layer is degraded
Solution Approach 1:
Carbon doping is applied locally and selectively in specific buffer layers (AlInGaN layers) rather than uniformly across all nitride layers. This localized doping approach allows the voltage withstanding to be improved in regions where it is most needed, while maintaining high crystalline quality in the undoped regions and in the active GaN layers.
Solution Approach 2:
The AlInGaN buffer layer acts as an intermediary layer that can tolerate carbon doping without significantly degrading crystalline quality. This intermediary layer absorbs the doping effects and protects the critical GaN active layers from degradation, allowing voltage withstanding to be improved while maintaining overall device quality.
Data Source
AI summary
A composite semiconductor substrate being able to improve voltage withstanding and crystalline quality is provided. A composite semiconductor substrate is equipped with an Si (silicon) substrate, an SiC (silicon carbide) layer formed on the surface of the Si substrate, an AlN (aluminum nitride) layer formed on the surface of the SiC layer, a composite layer formed on the surface of the AlN layer, and a GaN (gallium nitride) layer formed on the surface of the composite layer. The composite layer includes an AlN (aluminum nitride) layer and a GaN layer formed on the surface of the AlN layer. In at least one composite layer, the average density of C and Fe in the GaN layer is higher than the average density of C and Fe in the AlN layer.