Stacked Nanosheet Gate Work-Function Layout for Lower GIDL

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Solution Overview

Problem

In semiconductor device fabrication, particularly for nanosheet transistors, gate-induced drain leakage (GIDL) current remains a significant issue due to high electric fields across thin gate oxides, which affects device performance and density.

Innovation Solution

The use of a work-function metal (WFM) gradient in the gate structure, where a first type of WFM with a specific work-function is formed closer to the source or drain regions and a second type with a different work-function is formed in the central region, creating a tunnel with end regions closer to the source or drain than the central region, thereby relaxing the electric field across the gate oxide and reducing GIDL currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a uniform work-function metal is used in the gate structure, then the fabrication process is simple, but the GIDL current is high due to high electric field across the gate oxide

Engineering Contradiction:

ImproveGIDL currentVSAvoidgate structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The gate structure employs different work-function metals in different regions: a first work-function metal near the source/drain regions and a second work-function metal in the central region. This local differentiation creates a work-function gradient that reduces the electric field across the gate oxide, thereby reducing GIDL current while maintaining fabrication feasibility through selective deposition techniques.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The gate structure is segmented into multiple regions with different work-function metals rather than using a uniform material throughout. The tunnel is divided into a first set of end regions closer to the source/drain and a central region, allowing independent optimization of each region's electrical characteristics to minimize overall GIDL current.

Inventive Principle:

Principle #1Segmentation

2Area of stationary object

If thin gate oxide is used to increase device density, then device footprint is reduced, but GIDL current increases due to higher electric field

Engineering Contradiction:

Improvedevice footprintVSAvoidGIDL current

Core Design Contradiction:

Area of stationary objectVSLoss of energy

Solution Approach 1:

The invention changes the work-function parameter of the gate metal in different regions to compensate for the high electric field effects in thin gate oxide devices. By creating a work-function gradient through selective metal placement, the electric field distribution is modified, reducing band-to-band tunneling and GIDL current while maintaining the thin gate oxide architecture for high density.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If work-function metal gradient is implemented to reduce GIDL current, then GIDL current is reduced, but the fabrication process becomes more complex

Engineering Contradiction:

ImproveGIDL currentVSAvoidfabrication process

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The different work-function metals are deposited in a predetermined sequence during the fabrication process, with the first work-function metal applied near the source/drain regions before the second work-function metal is applied in the central region. This preliminary, staged deposition approach integrates the complex gradient structure into the standard fabrication flow, making the process manageable despite the increased complexity.

Inventive Principle:

Principle #10Preliminary action

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 reduces GIDL currents by creating a work-function gradient that alleviates the electric field stress across the gate oxide, enhancing the performance and density of nanosheet transistors.

Implementation Method 1

The mechanism responsible for GIDL current in MOSFETs is the band-to-band tunneling that can occur in the reverse biased channel-drain interface

Methodology Applied

Scientific EffectBand-to-band tunneling: Franz-Keldysh Effect

Data Source

PatentUS12191352B2Using different work-functions to reduce gate-induced drain leakage current in stacked nanosheet transistors

Publication Date: 2025.01.07 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

Embodiments of the invention are directed to a transistor device that includes a channel stack having stacked, spaced-apart, channel layers. A first source or drain (S/D) region is communicatively coupled to the channel stack. A tunnel extends through the channel stack, wherein the tunnel includes a central region and a first set of end regions. The first set of end regions is positioned closer to the first S/D region than the central region is to the first S/D region. A first type of work-function metal (WFM) is formed in the first set of end regions, the first WFM having a first work-function (WF). A second type of WFM is formed in the central region, the second type of WFM having a second WF, wherein the first WF is different than the second WF.