Nanosheet Transistor Cap Layer for Inner Spacer Etch Protection

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Solution Overview

Problem

The formation of inner spacers in semiconductor devices, particularly in nanostructure channel FETs, has not been entirely satisfactory in protecting the source/drain structure from damage during the gate replacement process, leading to reliability issues such as time-dependent dielectric breakdown and increased defects in epitaxial S/D features.

Innovation Solution

A nitride-based cap layer is formed between the inner spacers and the nanostructure channels through a nitridation process, which acts as an etch stop layer to prevent damage from etchant chemicals during the nanostructure formation process, thereby protecting the integrality of the epitaxial S/D features and reducing defects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If inner spacers are formed to protect source/drain structure during gate replacement, then protection is provided, but defects in epitaxial S/D features increase and reliability deteriorates

Engineering Contradiction:

Improveprotection of source/drain structureVSAvoiddamage from etchant chemicals

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A nitride-based cap layer is introduced as an intermediary between the inner spacer and the epitaxial source/drain features. This cap layer serves as an etch stop layer that mediates the interaction between etchant chemicals and the source/drain structure, preventing direct damage while allowing the inner spacer to maintain its protective function. The cap layer is formed through a nitridation process that converts the inner spacer material or deposits a nitride layer selectively at the interface.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The nitride-based cap layer is formed in advance before the gate replacement process occurs. By performing the nitridation process beforehand, the protective cap is already in place to prevent etchant damage during subsequent processing steps. This preliminary action ensures that the source/drain features are protected from the outset rather than attempting remediation after damage occurs.

Inventive Principle:

Principle #10Preliminary action

2Ease of manufacture

If conventional inner spacer formation is used, then manufacturing is simpler, but defects increase from 1×10^6/cm² to unacceptable levels

Engineering Contradiction:

Improveinner spacer formation processVSAvoiddefect density in epitaxial S/D features

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The invention changes the chemical composition parameter of the inner spacer by forming a nitride-based cap layer through nitridation. This parameter change transforms the material properties at the interface, creating an etch stop layer with different chemical resistance characteristics. The nitridation process modifies the composition to be more resistant to etchant chemicals, thereby reducing defect density while maintaining manufacturing feasibility.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If no cap layer is added, then device complexity is lower, but time-dependent dielectric breakdown occurs

Engineering Contradiction:

Improvenumber of layersVSAvoidtime-dependent dielectric breakdown

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The nitride-based cap layer acts as a cushioning layer formed beforehand to prevent time-dependent dielectric breakdown. By placing this protective layer between the inner spacer and the gate dielectric, it absorbs or prevents harmful effects that would otherwise accumulate over time and cause breakdown. This prior cushioning mitigates reliability issues before they manifest during device operation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 cap layer effectively reduces defects in epitaxial S/D features from 1×10^6/cm² to less than 1×10^4/cm² and increases the physical thickness of inner spacers, minimizing reliability issues like time-dependent dielectric breakdown.

Implementation Method 1

A nitride-based cap layer is formed between the inner spacers and the nanostructure channels through a nitridation process, which acts as an etch stop layer to prevent damage from etchant chemicals

Methodology Applied

Scientific EffectEtch stop layer:

Implementation Method 2

A nitride-based cap layer is formed between the inner spacers and the nanostructure channels through a nitridation process

Methodology Applied

Scientific EffectNitridation: Nitriding

Data Source

PatentUS20240072114A1Semiconductor device having nanosheet transistor and methods of fabrication thereof

Publication Date: 2024.02.29 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Various embodiments of the present disclosure provide a semiconductor device structure. In one embodiment, the semiconductor device structure includes a plurality of semiconductor layers vertically stacked over a substrate, a source/drain feature in contact with each of the plurality of the semiconductor layers, an inner spacer disposed between two adjacent semiconductor layers, a gate electrode layer surrounding a portion of each of the plurality of the semiconductor layers, a gate dielectric layer disposed between the semiconductor layer and the gate electrode layer, a gate spacer in contact with a portion of the gate dielectric layer. The semiconductor device structure further includes a first cap layer comprising a first portion disposed between and in contact with the source/drain feature and the gate spacer, and a second portion disposed between and in contact with gate spacer and the inner spacer.