GAA Transistor Air-Gap Structure for Dopant Diffusion Control

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Solution Overview

Problem

Integration of gate-all-around (GAA) transistor features is challenging, and existing methods do not adequately address issues such as dopant diffusion, threshold voltage uniformity, and short-channel effects in semiconductor device fabrication.

Innovation Solution

A method involving the formation of an air gap between inner spacers and source/drain epitaxial structures, using cyclic deposition and etching processes to create a diamond-shaped pre-layer structure, followed by epitaxial growth of strained materials, which prevents dopant diffusion and enhances mobility and reduces capacitance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional fabrication methods are used for GAA transistors, then manufacturing process compatibility is maintained, but dopant diffusion occurs leading to poor threshold voltage uniformity and increased short-channel effects

Engineering Contradiction:

Improvethreshold voltage uniformityVSAvoidshort-channel effects

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

An air gap is introduced as an intermediary structure between the inner spacer and source/drain epitaxial structures. This air gap acts as a physical barrier that prevents dopant diffusion while maintaining the structural integrity needed for GAA transistor operation, thereby improving threshold voltage uniformity and reducing short-channel effects

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The fabrication process employs cyclic deposition and etching to create a diamond-shaped pre-layer structure, followed by epitaxial growth of strained materials. These parameter changes in material structure and strain state prevent dopant out-diffusion and enhance carrier mobility, resolving the contradiction between manufacturing precision and device reliability

Inventive Principle:

Principle #35Parameter changes

2Productivity

If inner spacers and source/drain epitaxial structures are placed in direct contact, then device structure compactness is achieved, but dopant out-diffusion increases reducing device performance

Engineering Contradiction:

Improvedevice performanceVSAvoiddopant out-diffusion

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The air gap serves as a mediator that separates the inner spacer and source/drain epitaxial structures, preventing direct contact and the associated dopant out-diffusion. This intermediary structure maintains device performance by preserving dopant concentration while avoiding the need for direct structural contact

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If no air gap is formed, then manufacturing process is simpler, but parasitic capacitance increases reducing carrier mobility

Engineering Contradiction:

Improvefabrication simplicityVSAvoidcarrier mobility

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The introduction of an air gap changes the physical parameter of dielectric separation between structures. Air has lower permittivity than solid dielectrics, reducing parasitic capacitance and enhancing carrier mobility. The cyclic deposition and etching process makes this parameter change achievable through controlled diamond-shaped pre-layer formation

Inventive Principle:

Principle #35Parameter changes

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

Improves threshold voltage uniformity, reduces short-channel effects, and enhances carrier mobility and device performance by minimizing dopant out-diffusion and parasitic capacitance.

Implementation Method 1

an air gap is formed between the inner spacer and the source/drain epitaxial structure... prevents dopant diffusion

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 2

epitaxial growth of strained materials, which prevents dopant diffusion and enhances mobility

Methodology Applied

Scientific EffectStrain effect: Deformation

Implementation Method 3

using cyclic deposition and etching processes to create a diamond-shaped pre-layer structure

Methodology Applied

Scientific EffectChemical Vapor Deposition: Chemical Vapour Deposition

Implementation Method 4

using cyclic deposition and etching processes to create a diamond-shaped pre-layer structure

Methodology Applied

Scientific EffectEtching: Ablation

Implementation Method 5

an air gap is formed between the inner spacer and the source/drain epitaxial structure... reduces capacitance

Methodology Applied

Scientific EffectCapacitance reduction: Capacitance

Data Source

PatentUS12563780B2Semiconductor device structure and method for forming the same

Publication Date: 2026.02.24 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device structure includes nanostructures disposed over a substrate. The structure also includes a gate structure surrounding the nanostructures. The structure also includes inner spacers disposed over opposite sides of the gate structure. The structure also includes source/drain epitaxial structure disposed over opposite sides of the nanostructures. An air gap is disposed between the inner spacers and the source/drain epitaxial structure.