Ohmic Contact Structure for Group III Nitride Devices
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
There is a need for improved ohmic contact structures with enhanced surface morphology and well-defined edge features for Group III nitride semiconductor devices, as existing materials like silicon and gallium arsenide are not well-suited for high power and high frequency applications due to their small bandgaps and breakdown voltages.
Innovation Solution
The development of an ohmic contact structure for Group III nitride semiconductor devices, featuring a titanium layer, a nickel silicide layer formed by alternating silicon and nickel layers, and a metal cap layer, which achieves a root-mean-squared surface roughness of less than 10 nm, providing low contact resistance and chemical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional ohmic contact structures are used on Group III nitride semiconductor devices, then fabrication is simpler, but surface morphology is poor and edge features are not well-defined
Solution Approach 1:
The ohmic contact structure is divided into multiple distinct layers (titanium layer, nickel silicide layer, metal cap layer) with specific thicknesses and compositions. Each layer serves a particular function in achieving low contact resistance and smooth surface morphology, thereby resolving the contradiction between manufacturing precision and device complexity through systematic segmentation of the contact structure.
Solution Approach 2:
The patent applies different materials and thicknesses at different locations within the contact structure. The titanium layer has specific thickness (50-200 nm) optimized for adhesion to Group III nitride, the nickel silicide layer (50-200 nm) provides low contact resistance, and the metal cap layer (10-50 nm) offers chemical stability. This local optimization of material properties at each interface resolves the surface morphology and edge definition issues.
2Reliability
If simple metal layers are used for ohmic contacts, then device complexity is reduced, but contact resistance increases and chemical stability deteriorates
Solution Approach 1:
The ohmic contact structure employs a composite multi-layer configuration combining titanium, nickel silicide, and various metal cap layers (platinum, palladium, vanadium, tungsten, iridium, or rhodium). This composite structure achieves low contact resistance through the nickel silicide layer, chemical stability through the metal cap layer, and improved adhesion through the titanium layer, thereby resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The nickel silicide layer acts as an intermediary between the titanium layer and the metal cap layer, providing low contact resistance to the Group III nitride semiconductor while the metal cap layer serves as a protective intermediary against chemical degradation. This intermediary approach resolves the contradiction by distributing functional requirements across multiple intermediate layers.
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
The proposed ohmic contact structure achieves low contact resistance, chemical stability, and improved adhesion, enabling reliable performance in high power and high frequency applications, while maintaining surface smoothness and edge definition.
Implementation Method 1
an alternating series of one or more silicon layers and one or more nickel layers on a surface of the titanium layer opposite the surface of the Group III nitride semiconductor structure... The ohmic contact structure is thermally annealed such that the one or more silicon layers and the one or more nickel layers form a nickel silicide layer
Data Source
AI summary
Embodiments of an ohmic contact structure for a Group III nitride semiconductor device and methods of fabrication thereof are disclosed. In general, the ohmic contact structure has a root-mean-squared (RMS) surface roughness of less than 10 nanometers, and more preferably less than or equal to 7.5 nanometers, and more preferably less than or equal to 5 nanometers, and more preferably less than or equal to 2 nanometers, and even more preferably less than or equal to 1.5 nanometers.