Vertical III-V Epitaxy Using Masked Cavities to Block Dislocations
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Solution Overview
Problem
Current methods for growing thick layers of III-V materials, such as GaN, on silicon substrates face challenges like high dislocation densities and difficulty in achieving large substrate diameters, which are costly and inefficient for producing vertical microelectronic devices.
Innovation Solution
A method involving a stack of masking layers and sacrificial layers to control the growth of III-V materials, including a germination layer, masking layers, and selective removal of sacrificial layers to form cavities for epitaxial growth, resulting in low-defect vertical growth of thick epitaxial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN layers are grown on silicon substrates to reduce cost and access large substrates, then substrate cost and size are improved, but dislocation density increases to around 10^9 cm^-2
Solution Approach 1:
The growth process is segmented into multiple stages: initial growth on silicon substrate, transfer to intermediate carrier, and final growth on new substrate. This segmentation allows the harmful dislocations to remain confined to the first growth stage while subsequent stages occur on dislocation-free substrates, resolving the contradiction between cost-effective silicon substrates and low dislocation density requirements
Solution Approach 2:
An intermediate carrier substrate is introduced as a mediator between the silicon substrate and the final growth substrate. This intermediary enables the transfer of the GaN layer while preventing dislocation propagation, allowing the system to benefit from both the cost advantages of silicon substrates and the quality requirements of low-dislocation-density growth
2Area of stationary object
If GaN layers are grown on silicon substrates to access large substrate diameters, then substrate size is improved, but the ability to obtain thick layers deteriorates due to mesh parameter difference
Solution Approach 1:
The growth process is divided into stages performed on different substrates. The initial stage on silicon substrates establishes the GaN layer on large-diameter substrates, while subsequent stages are performed on new substrates that can accommodate thick layer growth without the constraints of silicon-GaN lattice mismatch, thus achieving both large substrate area and thick layer capability
3Reliability
If free-standing GaN substrates are used to grow vertical devices, then device performance is improved, but substrate cost increases and available substrate dimensions are limited to small sizes like 5 cm
Solution Approach 1:
The method uses disposable silicon substrates for the initial growth stage, which are then transferred away. These cheap substrates serve their purpose of initiating GaN layer growth but are not retained for the final device, allowing cost-effective manufacturing while maintaining device performance through subsequent growth on appropriate substrates
Solution Approach 2:
The intermediate carrier substrate acts as a mediator that temporarily holds the GaN layer grown on silicon, enabling transfer to final substrates. This intermediary process allows the system to use cheap silicon substrates for initial growth while ultimately achieving high-performance devices on substrates suitable for vertical device fabrication
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 enables low-defect, vertical growth of III-V materials, overcoming dislocation propagation and allowing for the production of thick layers on large substrates, suitable for high-performance vertical microelectronic devices.
Implementation Method 1
An epitaxial growth of a material made of the III-V material from the germination layer in the first opening and in the cavity, so as to form at least one first epitaxial layer
Implementation Method 2
The confinement during the growth of the first epitaxial layer, as well as the bent shape of the latter, makes it possible to avoid the propagation of the dislocations
Data Source
AI summary
A method for growing a III-V material may include forming at least one layer on a stack including a crystalline layer made of III-V material, a first masking layer surmounting the germination layer, the first masking layer having at least one first opening; depositing a second masking layer covering an upper face of the sacrificial layer; forming at least one second opening in the second masking layer; removing the sacrificial layer selectively at the first masking layer and at the second masking layer; epitaxially growing a material made of the III-V material from the germination layer; forming al least one third opening in the second masking layer; and epitaxially growing at least one material made of the III-V material from the first epitaxial layer.