GaN HEMT Threshold Voltage Control via Regrowth Layer Inclination
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Solution Overview
Problem
Conventional methods for manufacturing enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) face challenges in controlling threshold voltage and suffer from spatial non-uniformity and surface damage during processing.
Innovation Solution
A semiconductor device structure and manufacturing method involving a heterojunction body with a mask layer, regrowth layers, and a passivation layer, where the regrowth layers have inclined portions and through holes, allowing for precise control of the threshold voltage and minimizing surface damage through epi-growth processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods (thin AlGaN layer, gate-recess process, fluoride-based plasma treatment, oxygen plasma treatment, pn-junction gate, metal-insulator-semiconductor gate structure, annealed Pt-based gate metal) are used to manufacture enhancement-mode AlGaN/GaN HEMT, then the device can be fabricated, but the threshold voltage cannot be easily controlled and is not spatially uniform, and surface damage occurs during processing
Solution Approach 1:
The gate structure is segmented into multiple functional layers: a mask layer (first semiconductor layer) that defines the gate region, a regrowth layer (second semiconductor layer) that forms the active channel with controlled thickness, and a cap layer (third semiconductor layer) that protects the structure. This segmentation allows independent optimization of each layer's properties to achieve precise threshold voltage control while avoiding surface damage.
Solution Approach 2:
The mask layer is formed first to predefine the gate region boundaries before any gate-recess or plasma treatment steps. The regrowth layer is then epitaxially grown to precisely control the channel thickness and composition. This preliminary structuring eliminates the need for subsequent damaging surface treatments and ensures uniform threshold voltage across the gate area.
2Manufacturing precision
If gate-recess process is employed to control threshold voltage, then some control is achieved, but spatial non-uniformity and surface damage occur during the recess process
Solution Approach 1:
Instead of removing material (gate-recess) to control threshold voltage, the invention inverts the approach by precisely controlling the regrowth layer thickness during epitaxial growth. The threshold voltage is controlled by growing a thinner regrowth layer with specific Al composition, eliminating the need for damaging recess etching processes while achieving better spatial uniformity.
Solution Approach 2:
The mechanical/chemical removal process (gate-recess etching) is replaced with a controlled epitaxial growth process. The regrowth layer thickness and composition are controlled in-situ during deposition, providing atomic-level precision without the surface damage inherent in etching-based approaches.
3Ease of manufacture
If fluoride-based plasma treatment or oxygen plasma treatment is used during manufacturing, then surface processing is performed, but surface damage occurs and threshold voltage uniformity deteriorates
Solution Approach 1:
The mask layer serves as an intermediary protective structure during surface processing. It shields the underlying active regions from plasma damage while allowing necessary surface treatments to be performed on exposed areas. This intermediary layer prevents direct plasma exposure to the sensitive heterojunction interface, maintaining threshold voltage uniformity.
Solution Approach 2:
Damaging plasma-based surface treatment is replaced with controlled epitaxial growth of the regrowth layer. The desired surface properties and threshold voltage characteristics are achieved through in-situ growth parameters (temperature, pressure, composition ratios) rather than post-growth plasma modification, eliminating the associated surface 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 solution enables effective control of threshold voltage and reduces surface damage, resulting in a semiconductor device with improved uniformity and performance, specifically by interrupting two-dimensional electron gases at inclined portions and restoring them with appropriate voltage application.
Implementation Method 1
The regrowth layer is disposed on the first semiconductor layer and adjacent to the mask layer. The regrowth layer includes a main portion and at least one inclined portion.
Implementation Method 2
Since the heterojunction created by AlGaN and GaN forms a quantum well in the conduction band on the GaN side, a two-dimensional electron gap (2DEG) appears at the interface of AlGaN and GaN.
Data Source
AI summary
A semiconductor device including a substrate, a heterojunction body, a passivation layer, a source contact, a drain contact, and a gate contact. The heterojunction body disposed on or above the substrate includes a first semiconductor layer, a mask layer, a regrowth layer, and a second semiconductor layer. The first semiconductor layer is disposed on or above the substrate. The mask layer is disposed on or above a portion of the first semiconductor layer. The regrowth layer disposed on the first semiconductor layer and adjacent to the mask layer includes a main portion and at least one inclined portion. The second semiconductor layer is disposed on the mask layer and the regrowth layer. The passivation layer is disposed on the second semiconductor layer. The gate contact is disposed on the passivation layer, between the source contact and the drain contact, and at least above the inclined portion of the regrowth layer.