Composite Buffer Layers for Semiconductor Misfit Dislocation Reduction
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Solution Overview
Problem
The semiconductor industry faces challenges with misfit dislocations in epitaxial wafers due to lattice mismatch between different materials, leading to stress and reduced performance and lifetime of devices.
Innovation Solution
A wafer or material stack with a substrate and multiple composite buffer layers, where each layer consists of a transitional material (e.g., AlN) and a target material (e.g., GaN), with the thickness ratio of the transitional material to the target material decreasing along the growth direction, modulating stress and reducing misfit dislocations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer buffer structure is used, then the device structure is simple, but misfit dislocation increases due to lattice mismatch
Solution Approach 1:
The buffer layer is segmented into multiple composite buffer layers, each containing alternating sublayers of different materials (e.g., GaN and AlN). This segmentation allows gradual transition of lattice constants, reducing misfit dislocation while maintaining manageable structural complexity through systematic repetition of sublayer patterns.
Solution Approach 2:
Composite buffer layers are formed by combining multiple materials (GaN and AlN) in alternating sublayers. The composite structure leverages the different lattice constants of the constituent materials to create a graded transition zone, effectively reducing misfit dislocation between the substrate and the epitaxial layer.
2Reliability
If the thickness of transitional material layers is increased, then misfit dislocation is reduced, but the total buffer layer thickness increases
Solution Approach 1:
Different regions of the buffer structure have different local compositions and thicknesses. The transitional material layers (e.g., AlN) have varying thicknesses in different composite buffer layers, with the thickness decreasing in higher layers. This local variation optimizes misfit dislocation reduction at each interface while controlling the overall buffer thickness.
Solution Approach 2:
The thickness parameter of transitional material layers is systematically changed across different composite buffer layers. By decreasing the thickness of transitional layers in higher composite buffer layers while increasing the thickness of target material layers, the structure achieves progressive lattice constant transition, reducing misfit dislocation without requiring excessive total thickness.
3Reliability
If composite buffer layers with varying thickness ratios are used, then stress is modulated and misfit dislocation is reduced, but the manufacturing process complexity increases
Solution Approach 1:
The composite buffer layers are formed by periodic repetition of depositing sequences for different materials (e.g., GaN and AlN). This periodic action creates a regular pattern of alternating sublayers with controlled thickness ratios, enabling stress modulation and misfit dislocation reduction while maintaining a systematic, repeatable manufacturing process.
Solution Approach 2:
The thickness ratio parameter between transitional and target material sublayers is systematically changed across different composite buffer layers. By increasing the thickness ratio in higher layers, the structure achieves progressive stress relaxation and lattice constant transition, with the parameter changes following a controlled pattern that facilitates manufacturing.
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 effectively reduces misfit dislocations, improving the performance and lifetime of semiconductor devices by controlling epitaxial layer thickness and surface mobility, and ensuring a relaxed lattice constant in the top composite buffer layer.
Implementation Method 1
modulating stress and reducing misfit dislocations
Implementation Method 2
an epitaxial wafer is a high quality wafer made by an epitaxial growth process. During the epitaxial growth process, one or more crystalline overlayers (referred to as epitaxial layers) are deposited on a crystalline substrate
Data Source
AI summary
Disclosed is a wafer or a material stack for semiconductor-based optoelectronic or electronic devices that minimizes or reduces misfit dislocation, as well as a method of manufacturing such wafer of material stack. A material stack according to the disclosed technology includes a substrate; a basis buffer layer of a first material disposed above the substrate; and a plurality of composite buffer layers disposed above the basis buffer layer sequentially along a growth direction. The growth direction is from the substrate to a last composite buffer layer of the plurality of composite buffer layers. Each composite buffer layer except the last composite buffer layer includes a first buffer sublayer of the first material, and a second buffer sublayer of a second material disposed above the first buffer sublayer. The thicknesses of the first buffer sublayers of the composite buffer layers decrease along the growth direction.