Reusable SiC Substrate Epitaxy for Lower-Cost WBG Manufacturing
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Solution Overview
Problem
The high cost of wide bandgap semiconductor devices is predominantly due to the expensive substrate materials, particularly Silicon Carbide (SiC) substrates, which are complex and costly to produce, limiting the scalability and increasing defect rates as die sizes grow, leading to yield losses and reliability issues.
Innovation Solution
A method involving coating SiC substrates with a hard mask material, performing lithography to define patterned openings, etching to form reentrant trenches, and using Merged Epitaxial Lateral Overgrowth (MELO) to create micro voids, allowing for the growth of high-quality epitaxial layers and subsequent device fabrication while enabling kerfless wafer extraction and substrate reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SiC substrates are used for WBG semiconductor devices, then device performance and reliability are improved, but substrate cost increases significantly
Solution Approach 1:
The substrate is reused multiple times by extracting the epitaxial layer, restoring the substrate surface, and repeating the epitaxial growth process. This recovering approach reduces substrate cost while maintaining device reliability through consistent SiC material quality
Solution Approach 2:
The substrate processing is segmented into discrete steps: epitaxial layer growth, layer extraction, substrate restoration, and reuse. This segmentation allows independent optimization of each step to maintain reliability while reducing overall manufacturing cost
2Productivity
If substrate size is increased to reduce cost per device, then manufacturing efficiency improves, but defect density increases
Solution Approach 1:
The substrate surface is restored and prepared in advance through cleaning and surface treatment before each epitaxial growth cycle. This preliminary action ensures consistent low defect density across large substrates by eliminating accumulated defects from previous processing steps
Solution Approach 2:
The epitaxial growth process continues uninterrupted on the restored substrate surface, maintaining consistent crystal quality across the entire substrate area. This continuous process prevents defect formation that would occur with intermittent processing
3Manufacturing precision
If complex substrate fabrication processes are used to ensure quality, then substrate quality improves, but manufacturing complexity and cost increase
Solution Approach 1:
The complex ingot growth, cropping, wire sawing, and grinding processes are replaced by extracting the epitaxial layer directly from a simpler grown structure. This extraction approach takes out the unnecessary complex steps while maintaining substrate quality through controlled epitaxial growth
Solution Approach 2:
The fabrication process parameters are changed from mechanical processing (wire sawing, grinding) to chemical vapor deposition parameters for epitaxial growth. This parameter change simplifies the process while improving substrate quality through atomic-layer precision
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 reduces substrate costs, minimizes yield losses, and enhances device reliability by allowing for the efficient production of larger wafers with reduced defect densities, improving the thermal dissipation and performance of SiC and GaN semiconductor devices.
Implementation Method 1
coating the substrate with a hard mask material
Implementation Method 2
performing lithography to define patterned openings
Implementation Method 3
etching the substrate to form patterned trenches
Implementation Method 4
performing a buffer epitaxy on the substrate to form a uniform single crystal layer over the patterned trenches
Implementation Method 5
performing another epitaxy on the substrate using a fast epitaxial growth process to provide an active device epitaxial layer
Data Source
AI summary
A reusable silicon carbide or gallium nitride substrate is disclosed. A merge layer is formed in or on the substrate. Trenches are formed in the substrate. A trench pattern is configured to create a plurality of pillars in the substrate. The spacing between pillars is configured to support the formation of an epitaxial layer between the pillars grown by epitaxial lateral overgrowth. A surface of the merge layer comprises the epitaxial layer and a top surface of each pillar of the plurality of pillars. One or more epitaxial layers are grown by epitaxial vertical overgrowth overlying the merge layer. A plurality of devices are formed in the one or more epitaxial layers. The plurality of devices is separated from the substrate where the exfoliation occurs below the surface of the merge layer. A portion of the merge layer is coupled to the plurality of devices after exfoliation.