Epitaxial Substrate Lattice Misfit Relief
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Solution Overview
Problem
The formation of high-quality nitride films on silicon substrates is hindered by lattice constant differences, misfit dislocations, and thermal stress, leading to issues like dislocation density, film cracking, and warping, which affects the quality of semiconductor devices such as HEMT.
Innovation Solution
A nitride epitaxial substrate is developed using a single-crystal silicon base substrate with a (111) orientation, featuring a first group-III nitride layer with multiple defects and a three-dimensional asperity surface interface, along with an amorphous interface layer and a superlattice structure, to relieve lattice misfit and reduce dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a nitride film is formed on a silicon substrate, then the cost is reduced and integration with silicon circuit devices is improved, but dislocation density increases and film quality deteriorates due to lattice constant differences
Solution Approach 1:
A buffer layer is introduced between the silicon substrate and the nitride film to serve as an intermediary structure. This buffer layer absorbs the lattice mismatch stress and prevents direct contact between the incompatible silicon and nitride materials, thereby reducing dislocation density while enabling cost-effective silicon substrate usage
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers including the silicon substrate, buffer layer, and nitride film. This composite approach allows each layer to perform its specific function - the silicon substrate provides cost advantage and electrical properties, while the buffer layer manages stress and the nitride film provides the desired semiconductor characteristics
2Manufacturing precision
If a nitride film is grown on a silicon substrate at high temperature, then epitaxial growth is achieved, but thermal stress causes film cracking and substrate warping due to thermal expansion coefficient differences
Solution Approach 1:
The buffer layer is prepared in advance before depositing the nitride film, creating a cushioning structure that anticipates and absorbs the thermal expansion stress. This pre-positioned buffer layer prevents film cracking and substrate warping during the high-temperature epitaxial growth process by accommodating the differential thermal expansion between silicon and nitride materials
3Ease of manufacture
If trimethylgallium is used as a source gas for nitride material deposition, then nitride film formation is enabled, but liquid compound formation with silicon inhibits epitaxial growth
Solution Approach 1:
The buffer layer acts as an intermediary barrier between the silicon substrate and the trimethylgallium source gas. This intermediate structure prevents the formation of liquid compounds between trimethylgallium and silicon, thereby eliminating the inhibition of epitaxial growth while still enabling effective nitride film deposition
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 enables the creation of nitride epitaxial substrates with crystal quality comparable to those using sapphire or SiC substrates, while reducing costs and improving electron mobility and breakdown voltage in semiconductor devices.
Implementation Method 1
an amorphous interface layer is formed between the base substrate and the first group-III nitride layer
Implementation Method 2
a first group-III nitride layer with multiple defects and a three-dimensional asperity surface interface
Implementation Method 3
the nitride material has a larger thermal expansion coefficient value compared with silicon, and thus a tensile stress acts on the inside of a nitride film in the process of decreasing the temperature to about a room temperature after epitaxially-growing the nitride film on a silicon substrate at a high temperature
Implementation Method 4
a group of group-III nitride layers are formed on a base substrate including single-crystal silicon
Data Source
AI summary
An epitaxial substrate, in which a group of group-III nitride layers is formed on a single-crystal silicon substrate so that a crystal plane is approximately parallel to a substrate surface, comprises: a first group-III nitride layer formed of AlN on the base substrate; a second group-III nitride layer formed of InxxAlyyGazzN (xx+yy+zz=1, 0≦xx≦1, 0<yy≦1 and 0<zz≦1) on the first group-III nitride layer; and at least one third group-III nitride layer epitaxially-formed on the second group-III nitride layer, wherein: the first group-III nitride layer is a layer containing multiple defects including at least one type of a columnar crystal, a granular crystal, a columnar domain and a granular domain; and an interface between the first group-III nitride layer and the second group-III nitride layer is a three-dimensional asperity surface.