SiC Epitaxial Lift-Off Using Micro Voids for Substrate Reuse
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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, and current methods for increasing substrate size or kerfless extraction face yield losses and limitations in wafer thickness.
Innovation Solution
A method involving coating the SiC substrate 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 with minimal substrate contribution, enabling kerfless wafer extraction and substrate reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional SiC substrate fabrication processes are used, then substrate quality is maintained, but substrate cost contributes over half of the final device cost
Solution Approach 1:
The patent implements substrate reuse by extracting the epitaxial layer from the SiC substrate, allowing the substrate to be cleaned and reused for additional epitaxial growth cycles. This recovers the expensive substrate material, dramatically reducing the cost contribution of substrates to the final device while maintaining substrate quality through controlled reuse processes
Solution Approach 2:
The patent extracts the epitaxial layer containing the fabricated devices from the SiC substrate through controlled separation processes. This extraction enables the substrate to be recovered and reused, separating the value-added epitaxial layer from the reusable substrate, thereby reducing the effective cost of substrate material per device
2Productivity
If larger substrate sizes are used to reduce kerf loss, then device yield improves, but substrate fabrication complexity and cost increase
Solution Approach 1:
By enabling substrate reuse through epitaxial layer extraction, the patent makes it economically viable to use larger substrate sizes. The recovered substrate can undergo multiple growth cycles, amortizing the complexity and cost of large substrate fabrication across multiple device batches, thereby improving overall device yield without proportionally increasing fabrication complexity
3Loss of substance
If kerfless extraction methods are used, then material waste is reduced, but yield losses occur during the cleaving process
Solution Approach 1:
The patent performs preliminary actions to prepare the substrate for clean extraction, including forming separation layers, controlling epitaxial growth interfaces, and preparing the substrate structure before device fabrication. These preliminary steps enable subsequent kerfless extraction to proceed with minimal yield loss by creating optimal conditions for clean separation
Solution Approach 2:
The patent replaces traditional mechanical cleaving methods with controlled separation processes that grow epitaxial layers with built-in separation interfaces. This substitution eliminates the need for forceful mechanical separation that causes yield losses, achieving kerfless extraction with preserved device integrity and yield
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 the substrate cost contribution while maintaining low defect densities, enabling the production of larger, high-quality semiconductor devices with improved yield and reliability, and allows for the reuse of SiC substrates, thereby lowering overall device production costs.
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
removing the hard mask using a chemical process from the substrate
Implementation Method 5
performing a buffer epitaxy on the substrate to form a uniform single crystal layer over the patterned trenches
Implementation Method 6
performing another epitaxy on the substrate using a fast epitaxial growth process to provide an active device epitaxial layer
Data Source
AI summary
A method for manufacturing a wide band gap semiconductor device using a substrate of SiC wafer is disclosed. The method includes coating the substrate with a hard mask material, performing lithography to define patterned openings in the hard mask material of the substrate, etching the substrate to form patterned trenches from the defined patterned openings, removing the hard mask using a chemical process from the substrate, cleaning the substrate with the patterned trenches, performing epitaxy on the substrate to form a uniform single crystal layer over the patterned trenches to create a plurality of micro voids, kiss polishing the substrate, performing another epitaxy on the substrate using a fast epitaxial growth process to provide an active device epitaxial layer suitable to fabricate SiC devices, and after fabrication of the SiC devices, severing the plurality of micro voids to extract the SiC devices from the substrate of the SiC wafer.