GaN Transistor Buffer Structure for Current Collapse Uniformity
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Solution Overview
Problem
Gallium nitride (GaN) transistors face challenges with current collapse performance due to non-uniform intrinsic carbon doping across wafers, leading to reduced production yield and increased costs, as well as issues with surface micro-pitting and leakage from exposed epitaxially deposited top aluminum gallium nitride layers.
Innovation Solution
The implementation of a dual superlattice stack buffer structure with extrinsically carbon doped buffer layers and a silicon nitride cap layer, which includes alternating pairs of aluminum nitride and aluminum gallium nitride sublayers, and aluminum nitride and gallium nitride sublayers, to enhance carbon doping uniformity and mitigate current collapse, while the silicon nitride cap layer prevents surface micro-pitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intrinsic carbon doping is increased to improve current collapse performance, then current collapse performance is improved, but epitaxial deposition quality deteriorates due to decreased deposition temperature
Solution Approach 1:
A carbon-doped aluminum gallium nitride layer is introduced as an intermediary between the aluminum nitride buffer layer and the gallium nitride channel layer. This intermediary layer provides the necessary carbon doping for current collapse mitigation while allowing the epitaxial deposition to proceed at optimal temperatures, thus resolving the contradiction between improving current collapse performance and maintaining epitaxial deposition quality
Solution Approach 2:
The invention changes the parameter of carbon doping from intrinsic (through metal organic source) to extrinsic (through additional carbon source gas), and adjusts the deposition temperature to optimize both carbon doping levels and epitaxial deposition quality simultaneously, resolving the trade-off between current collapse performance and material quality
2Reliability
If intrinsic carbon doping is used to improve current collapse performance, then current collapse performance is improved, but doping uniformity across the wafer deteriorates
Solution Approach 1:
The carbon-doped aluminum gallium nitride layer serves as an intermediary that enables uniform extrinsic carbon doping across the entire wafer surface, ensuring consistent current collapse performance from center to edge regions, thereby resolving the uniformity issue inherent in intrinsic carbon doping methods
Solution Approach 2:
By switching from intrinsic carbon doping to extrinsic carbon doping with controlled carbon source gas flow, the invention achieves uniform carbon distribution across the wafer, resolving the non-uniform doping issue that plagues intrinsic doping methods
3Productivity
If the top aluminum gallium nitride layer is exposed during processing, then transistor fabrication is completed, but surface micro-pitting and leakage occur
Solution Approach 1:
The silicon nitride cap layer is deposited in advance to protect the aluminum gallium nitride surface from oxidation and micro-pitting during subsequent fabrication processing steps, preventing reliability issues before they occur
Solution Approach 2:
The silicon nitride cap layer acts as an intermediary protective barrier between the aluminum gallium nitride surface and the processing environment, shielding the surface from harmful effects during fabrication while allowing the process to proceed to completion
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 solution improves the uniformity of carbon doping across the wafer, reducing current collapse and increasing production yield, while also preventing surface micro-pitting and leakage issues, thereby enhancing the reliability and cost-effectiveness of GaN transistors.
Implementation Method 1
Epitaxial deposition of buffer layers and some GaN transistors involves intrinsic carbon doping due to use of a metal organic source
Implementation Method 2
intrinsic carbon doping helps current collapse performance. Improved current collapse performance can be aided by increased carbon doping
Implementation Method 3
some GaN transistor designs include an epitaxially deposited top aluminum gallium nitride (AlGaN) layer that is exposed during subsequent processing, leading to oxidation and surface micro-pitting
Implementation Method 4
a hetero-epitaxy structure over the buffer, and a transistor over or in the hetero-epitaxy structure
Data Source
AI summary
Fabrication methods and gallium nitride transistors, in which an electronic device includes a substrate, a buffer structure, a hetero-epitaxy structure over the buffer structure, and a transistor over or in the hetero-epitaxy structure. In one example, the buffer structure has an extrinsically carbon doped gallium nitride layer over a dual superlattice stack or over a multilayer composition graded aluminum gallium nitride stack, and a silicon nitride cap layer over the hetero-epitaxy structure.