AlGaN/GaN HEMT Passivation via Thin SiN Barrier Layer

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Solution Overview

Problem

Existing methods for passivating AlGaN/GaN high electron mobility transistors (HEMTs) using plasma-enhanced CVD (PECVD) SiN films often result in plasma damage to the AlGaN surface, leading to device reliability issues such as carrier scattering and current collapse due to low-frequency plasma ion energy.

Innovation Solution

The introduction of a thin high-frequency (HF) PECVD SiN barrier layer before the deposition of a thick HF/LF SiN passivation layer suppresses plasma damage by preventing nitrogen ions from being accelerated towards the AlGaN surface, using bi-layer or tri-layer SiN passivation configurations to protect the surface during the PECVD process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If PECVD SiN passivation is applied to AlGaN/GaN HEMTs, then surface passivation quality is improved, but plasma damage to the AlGaN surface occurs due to low-frequency plasma ion energy

Engineering Contradiction:

Improvesurface passivation qualityVSAvoidplasma damage to AlGaN surface

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A thin barrier layer (5-20 nm) of AlN or SiN is deposited between the AlGaN surface and the thick PECVD SiN passivation layer. This intermediary barrier layer absorbs or blocks the harmful low-frequency plasma ions during PECVD processing, preventing them from reaching and damaging the AlGaN surface, while still allowing the thick SiN layer to provide effective surface passivation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The thin barrier layer is deposited in advance before the thick PECVD SiN passivation layer. This preliminary protective layer is formed under conditions that minimize plasma damage (using high-frequency plasma or low ion energy), establishing a protective shield that prevents subsequent plasma damage during the deposition of the thick passivation layer.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If low-frequency plasma is used in PECVD SiN deposition, then deposition efficiency is improved, but nitrogen ions are accelerated towards the AlGaN surface causing damage

Engineering Contradiction:

Improvedeposition efficiencyVSAvoidnitrogen ion acceleration and surface damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The thin barrier layer serves as a mediator that allows the use of low-frequency plasma for efficient deposition of the thick SiN layer while preventing the accelerated nitrogen ions from reaching and damaging the AlGaN surface. The barrier layer absorbs the ion bombardment energy, enabling high-productivity deposition without surface damage.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If a thick SiN passivation layer is deposited directly on AlGaN surface, then passivation effectiveness is improved, but surface traps are created leading to current collapse

Engineering Contradiction:

Improvepassivation effectivenessVSAvoidsurface traps and current collapse

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The thin barrier layer is deposited first to create a clean, damage-free interface with the AlGaN surface. This preliminary layer prevents the formation of surface traps during subsequent processing, ensuring that when the thick SiN passivation layer is added, it builds upon a trap-free foundation, maintaining effective passivation without current collapse.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The thin barrier layer acts as an intermediary that prevents direct interaction between the harmful PECVD plasma and the AlGaN surface. By absorbing the plasma damage, it prevents the creation of surface traps that would otherwise occur at the AlGaN/SiN interface, thereby eliminating the source of current collapse while maintaining passivation effectiveness.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 prevents plasma damage and current collapse, enhancing the electrical performance of AlGaN/GaN HEMTs by reducing surface traps and improving mobility and drain current density, while maintaining low stress and refractive index uniformity.

Implementation Method 1

Damage-free plasma-enhanced CVD passivation of AlGaN/GaN high electron mobility transistors

Methodology Applied

Scientific EffectPlasma-enhanced chemical vapor deposition: Plasma Enhanced Chemical Vapour Deposition

Implementation Method 2

low-frequency plasma ion energy

Methodology Applied

Scientific EffectPlasma: Plasma

Data Source

PatentUS9960266B2Damage-free plasma-enhanced CVD passivation of AlGaN/GaN high electron mobility transistors

Publication Date: 2018.05.01 THE GOVERNMENT OF THE UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY DEPARTMENT OF HEALTH & HUMAN SERVICES

AI summary

Passivated AlGaN/GaN HEMTs having no plasma damage to the AlGaN surface and methods for making the same. In a first embodiment, a thin HF SiN barrier layer is deposited on the AlGaN surface after formation of the gate. A thick HF/LF SiN layer is then deposited, the thin HF SiN layer and the thick HF/LF Sin layer comprising bi-layer SiN passivation on the HEMT. In a second embodiment, a first thin HF SiN barrier layer is deposited on the AlGaN surface before formation of the gate and is annealed. Following annealing of the first SiN layer, the gate is formed, and a second HF SiN barrier layer is deposited, followed by a thick HF/LF SiN layer, the three SiN layers comprising tri-layer SiN passivation on the HEMT.