TaN/Al Ohmic Electrode for GaN Transistor Oxidation Control
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Solution Overview
Problem
Existing methods for forming ohmic electrodes in GaN-based semiconductor transistors, such as Ti/Al and Ta/Al, face issues like oxidation and reduced durability, especially at high temperatures, and require complex multi-target film formation, affecting uniformity and yield, particularly for large-diameter wafers.
Innovation Solution
A method involving the formation of a tantalum nitride (TaN) layer followed by an aluminum (Al) layer, with heat treatment between 520° C. and 600° C., to create a TaN/Al-based ohmic electrode that suppresses oxidation and electromigration, allowing for single-target film formation and improved process flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ti/Al or Ta/Al electrode structure is used, then electrode durability at high temperature is improved, but oxidation of Ti or Ta occurs leading to increased resistance
Solution Approach 1:
A TaN barrier layer is introduced as an intermediary between the active layer and the Al electrode layer. This TaN layer prevents oxidation of the Al layer while maintaining good ohmic contact with the active layer, thus resolving the oxidation problem without sacrificing electrode durability
Solution Approach 2:
The electrode structure uses a composite of TaN and Al layers. The TaN layer provides oxidation resistance and good contact with GaN, while the Al layer provides low resistance and high conductivity, achieving both durability and low resistance
2Object-affected harmful factors
If multi-target film formation apparatus is used to form Ti/Al or Ta/Al electrode, then oxidation is prevented, but manufacturing complexity and process time increase
Solution Approach 1:
The TaN layer serves as a protective intermediary that allows the Al layer to be deposited without requiring a multi-target apparatus. The TaN layer's low oxygen affinity protects the Al from oxidation during deposition, enabling use of simpler single-target equipment
3Reliability
If TaN/Al electrode with heat treatment at 700°C or higher is used, then ohmic contact is achieved, but damage to GaN-based semiconductor occurs
Solution Approach 1:
The heat treatment temperature is optimized to a specific range (400-600°C) that is sufficient to achieve good ohmic contact between TaN and Al without causing damage to the GaN-based semiconductor substrate. This parameter optimization resolves the contradiction between achieving ohmic contact and avoiding substrate damage
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 TaN/Al-based ohmic electrode achieves reliable ohmic contact with increased process freedom, improved durability at high temperatures, and enhanced productivity by preventing oxidation and reducing contact resistance, while maintaining the Al layer's integrity.
Implementation Method 1
a process of forming the ohmic electrode in ohmic contact with the active layer by heat treating the first layer and the second layer at a temperature of from 520° C. to 600° C.
Implementation Method 2
In the multi-target film-formation apparatus, however, sputtering of a target is performed from an oblique direction.
Data Source
AI summary
A method of producing a semiconductor transistor involving formation of an ohmic electrode on an active layer composed of a GaN-based semiconductor includes a process of forming a first layer 11 composed of tantalum nitride on an active layer 3 and a second layer 12 composed of Al layered on the first layer 11 and a process of forming ohmic electrodes 9s and 9d in ohmic contact with the active layer 3 by heat treating the first layer 11 and the second layer 12 at a temperature of from 520° C. to 600° C.