Screen Layer Controls Metal Diffusion in HEMT Ohmic Contacts
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Solution Overview
Problem
In semiconductor technology, forming consistent and uniform ohmic contacts in high electron mobility transistors (HEMTs) is challenging due to variations in metal diffusion during fabrication, leading to either shallow or deep metal penetration, which affects the quality of the metal-semiconductor junction.
Innovation Solution
The introduction of a screen layer, such as aluminum nitride (AlN), in the HEMT structure helps control metal diffusion, ensuring a more uniform and accurate depth of metal penetration, thereby improving the reliability and uniformity of ohmic contacts between metal electrodes and the semiconductor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal diffusion is performed during HEMT fabrication, then ohmic contact is formed between metal electrode and semiconductor, but metal penetration depth varies due to fabrication variations, leading to inconsistent contact quality
Solution Approach 1:
A screen layer is introduced as an intermediary between the metal electrode and the semiconductor channel layer. This screen layer mediates the diffusion process, allowing controlled metal penetration to form ohmic contacts while preventing excessive diffusion that would compromise device performance. The screen layer acts as a buffer that absorbs fabrication variations, ensuring consistent contact quality across different manufacturing runs.
Solution Approach 2:
The screen layer is formed in advance before the metal electrode deposition and diffusion process. This preliminary structure is prepared with specific material composition and thickness to pre-determine the diffusion characteristics, ensuring that subsequent metal diffusion produces uniform penetration depth regardless of fabrication variations.
2Reliability
If metal diffusion depth is increased to ensure ohmic contact, then contact reliability improves, but metal penetration becomes too deep causing charge carrier leakage
Solution Approach 1:
The screen layer serves as a controlled intermediary that permits necessary metal diffusion for ohmic contact formation while blocking excessive diffusion that would cause charge carrier leakage. By adjusting the screen layer's material composition and thickness, the diffusion process is precisely controlled to achieve the optimal balance between contact reliability and leakage prevention.
Solution Approach 2:
The screen layer's material parameters (composition, thickness, doping concentration) are optimized to control the diffusion characteristics. By changing these parameters, the diffusion depth is precisely controlled to achieve sufficient ohmic contact while preventing metal penetration that would cause charge carrier leakage in the channel layer.
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 screen layer enhances the formation of reliable ohmic contacts by reducing the impact of fabrication variations, resulting in improved conductivity and reduced production costs, leading to higher yield and performance consistency in HEMT devices.
Implementation Method 1
control metal diffusion, ensuring a more uniform and accurate depth of metal penetration
Data Source
AI summary
A transistor includes a substrate, a channel layer over the substrate and an active layer over the channel layer. The active layer includes a first portion and a screen layer over the first portion. The transistor includes a metal layer over the screen layer.