Nanosheet FET Continuous Spacer for STI Leakage Isolation

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Solution Overview

Problem

The excessive recess of shallow trench isolation (STI) in nanosheet field-effect transistors (FETs) leads to topology issues, increasing the risk of yield and reliability failures due to chemical leakage through residual openings at the bottom corners of spacers.

Innovation Solution

A semiconductor device with a continuous spacer layer from the gate sidewalls to the STI is implemented to improve gate-source/drain isolation in nanosheet FETs, minimizing topology and preventing chemical leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the shallow trench isolation (STI) is recessed to accommodate the gate stack, then the gate-all-around structure is achieved, but excessive recess creates topology issues and chemical leakage paths

Engineering Contradiction:

Improvegate-all-around structureVSAvoidchemical leakage prevention

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The spacer layer is segmented into two functional portions: a first portion that fills the STI recess and a second portion that forms a continuous barrier from the gate sidewall to the STI. This segmentation allows each portion to address specific requirements - the first portion accommodates the gate stack while the second portion prevents chemical leakage

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The continuous spacer layer acts as an intermediary barrier between the gate region and the STI, preventing direct chemical leakage paths while maintaining the recessed STI structure needed for gate-all-around formation

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the STI is recessed to enable gate formation, then transistor density is improved, but residual openings at spacer bottom corners create leakage paths

Engineering Contradiction:

Improvetransistor densityVSAvoidisolation completeness

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The spacer layer is formed preliminarily to create a continuous barrier before subsequent processing steps. The spacer material is deposited to ensure complete coverage and continuity from the gate sidewall to the STI, preventing leakage paths before they can form

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The spacer layer exhibits different local qualities: the first portion has fill characteristics suitable for STI accommodation, while the second portion has barrier characteristics that prevent chemical leakage. This local differentiation addresses both density and precision requirements

Inventive Principle:

Principle #3Local quality

3Reliability

If a continuous spacer layer is formed from gate sidewalls to STI, then chemical leakage is prevented, but device structure complexity increases

Engineering Contradiction:

Improveisolation effectivenessVSAvoidspacer layer structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The continuous spacer layer serves multiple functions simultaneously: it provides mechanical support, ensures chemical isolation, defines critical dimensions, and maintains structural integrity. This multi-functionality justifies the additional structural element by consolidating multiple requirements into a single component

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20250203993A1Nanosheet field effect transistor with continuous spacer

Publication Date: 2025.06.19 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A semiconductor device includes a shallow trench isolation (STI), a plurality of fins over the STI, a plurality of gate regions, and a spacer layer. Each of the plurality of fins includes at least a source/drain region. Portions of the STI between the plurality of fins and portions of the STI between the plurality of gate regions are isolated by the first spacer layer.