HEMT Threshold Voltage Tuning via Fluorine Diffusion Gradient

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Solution Overview

Problem

Existing semiconductor technologies face challenges in efficiently transitioning between enhancement mode (E-mode) and depletion mode (D-mode) high electron mobility transistors (HEMT) without altering the manufacturing process, particularly in adjusting the threshold voltage for these devices.

Innovation Solution

The integration of a fluorine ion concentration gradient in the barrier layer and controlled thermal annealing processes, combined with gate voltage adjustments, allows for the formation of both E-mode and D-mode HEMT devices by diffusing fluorine ions into and away from the two-dimensional electron gas layer, thereby adjusting the threshold voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If fluorine ions are diffused into the channel layer away from the 2DEG layer, then the threshold voltage becomes negative (D-mode HEMT), but the fluorine ion concentration adjacent to the 2DEG layer becomes lower than away from it

Engineering Contradiction:

Improvemode flexibilityVSAvoidfluorine ion concentration distribution

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by pre-distributing fluorine ions in the barrier layer before thermal annealing, creating a concentration gradient that will diffuse into the channel layer during subsequent processing. This preliminary setup enables the desired final concentration distribution without requiring complex in-situ doping equipment.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent utilizes parameter changes by controlling the thermal annealing temperature and duration to precisely regulate the diffusion of fluorine ions from the barrier layer into the channel layer. By adjusting these parameters, the final fluorine ion concentration distribution can be optimized to achieve the desired threshold voltage characteristics.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If the same device structure is used for both E-mode and D-mode HEMTs, then manufacturing process complexity is reduced, but threshold voltage adjustment becomes more challenging

Engineering Contradiction:

Improveprocess simplicityVSAvoidthreshold voltage control

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The patent applies local quality by creating a non-uniform fluorine ion concentration distribution within the channel layer, with higher concentrations away from the 2DEG layer and lower concentrations adjacent to it. This localized variation in doping concentration enables precise control of the threshold voltage while maintaining a unified device structure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent achieves universality by designing a single device structure that can function in both E-mode and D-mode configurations. The same HEMT structure with strategically distributed fluorine ions can be tuned to exhibit either enhancement mode or depletion mode characteristics, eliminating the need for separate device designs.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If fluorine ions are concentrated away from the 2DEG layer, then D-mode operation is achieved, but the electron mobility near the interface may be affected

Engineering Contradiction:

Improvedepletion mode operationVSAvoidelectron transport performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

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 enables the same semiconductor device structure to function as either E-mode or D-mode HEMT by manipulating fluorine ion distribution, offering versatile threshold voltage adjustment without altering the manufacturing process steps.

Implementation Method 1

diffusing fluorine ions into and away from the two-dimensional electron gas layer

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

controlled thermal annealing processes

Methodology Applied

Scientific EffectThermal annealing: Annealing

Implementation Method 3

integration of a fluorine ion concentration gradient in the barrier layer

Methodology Applied

Scientific EffectIon implantation: Ion Implantation

Data Source

PatentUS20250351399A1Method of forming semiconductor device

Publication Date: 2025.11.13 UNITED MICROELECTRONICS CORP

AI summary

Provided is a semiconductor device including an enhancement mode (E-mode) high electron mobility transistor (HEMT). The E-mode HEMT includes a substrate, and a channel layer disposed on the substrate. A barrier structure disposed on the channel layer. A pair of source/drain (S/D) metals respectively disposed on the channel layer at opposite sides of the barrier structure. A gate metal disposed on the barrier structure between the pair of S/D metals. The channel layer has a two-dimensional electron gas (2DEG) layer close to an interface between the channel layer and the barrier structure. A fluorine ion concentration in the channel layer adjacent to the 2DEG layer is greater than that away from the 2DEG layer.