Nitride Superlattice Epitaxy for Breakdown Voltage Without Wafer Bowing
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Solution Overview
Problem
Semiconductor devices with nitride semiconductors face issues of strain and bowing due to lattice constant differences, leading to reduced breakdown voltage and potential wafer cracking during cooling, especially when doped layers with dopants like carbon and iron are used in superlattice stacks.
Innovation Solution
The use of alternately stacked doped and undoped films in an epitaxial manner, with undoped films grown above doped layers to recover crystallinity and roughness, and insertion of undoped films between doped layers to prevent complete bowing, along with adjusting aluminum and gallium concentrations to mitigate bowing effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doped layers with dopants (carbon, iron) are used in the superlattice stack, then the breakdown voltage is improved, but the crystallinity and roughness deteriorate
Solution Approach 1:
The superlattice stack is segmented into alternating doped and undoped film layers. The undoped layers act as buffer regions that restore crystallinity and surface roughness between the doped layers, which provide high breakdown voltage. This segmentation allows each layer type to perform its optimal function without compromising the other.
Solution Approach 2:
Different regions of the superlattice stack have different doping characteristics. The doped layers contain carbon and/or iron dopants for high breakdown voltage, while the undoped layers maintain pure crystalline structure for surface quality. This local differentiation of properties resolves the contradiction between electrical performance and structural quality.
2Reliability
If doped layers are used throughout the superlattice stack, then the breakdown voltage is improved, but wafer bowing and cracking occur during cooling
Solution Approach 1:
The superlattice stack is divided into alternating doped and undoped layers. The undoped layers serve as stress-relief zones that prevent cumulative bowing and cracking during thermal cooling, while the doped layers maintain the required breakdown voltage performance.
Solution Approach 2:
The undoped film layers act as intermediary elements between the doped layers. These intermediary undoped layers accommodate thermal stress and prevent the propagation of cracks, thereby protecting the overall wafer structure while allowing the doped layers to provide high breakdown voltage.
3Manufacturing precision
If undoped films are grown above doped layers, then crystallinity and roughness are recovered, but the manufacturing process complexity increases
Solution Approach 1:
The epitaxial growth process follows a periodic pattern, alternating between depositing doped layers and undoped layers. This periodic cycling of doping and undoped growth phases systematically restores crystallinity at regular intervals, making the process complexity manageable and repeatable.
Solution Approach 2:
The doping parameters (presence of carbon and/or iron dopants) are changed periodically during epitaxial growth. By cycling between doped and undoped conditions, the process achieves both high breakdown voltage and restored crystallinity, with the parameter changes being systematically controlled.
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 raises the breakdown voltage of semiconductor devices while preventing wafer cracking by maintaining favorable crystallinity and roughness, and resolving bowing issues, ensuring stable epitaxial growth and manufacturing processes.
Implementation Method 1
dopants are implanted into at least one film in the superlattice stack, so as to form the doped layer
Implementation Method 2
a GaN layer and an aluminum gallium nitride (AlGaN) layer are sequentially grown on the substrate in an epitaxial manner
Data Source
AI summary
A semiconductor device includes a substrate, an initial layer, and a superlattice stack. The initial layer is located on the substrate and includes aluminum nitride (AlN). The superlattice stack is located on the initial layer and includes a plurality of first films, a plurality of second films and at least one doped layer, and the first films and the second films are alternately stacked on the initial layer, wherein the at least one doped layer is arranged in one of the first films and the second films, and dopants of the at least one doped layer are selected from a group consisting of carbon, iron, and the combination thereof.