Backside Power Rail FinFET Contacts Without Source/Drain Etch Damage

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Solution Overview

Problem

The semiconductor industry faces challenges in forming metal contacts on the backside of FinFET or Nanosheet FET devices without damaging the source/drain features, due to low etch selectivity of n-type source/drain materials.

Innovation Solution

A corner portion of the semiconductor material is kept during backside semiconductor removal, protecting the source/drain features and allowing them to be formed with a convex surface, which increases their volume and improves device performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If backside semiconductor removal is performed to form metal contacts, then metal contacts can be formed on the backside, but the source/drain features may be damaged due to low etch selectivity

Engineering Contradiction:

Improvebackside contact formationVSAvoidsource/drain feature integrity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

A corner portion of the semiconductor material is retained during backside removal as a protective measure before the actual backside contact formation. This preliminary retention of material serves as a sacrificial buffer that prevents etchant from reaching and damaging the source/drain features during subsequent processing steps.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The corner portion of the semiconductor material acts as an intermediary protective layer between the etchant and the source/drain features. This intermediate structure absorbs the harmful effect of the etchant, allowing backside contact formation to proceed without damaging the critical source/drain regions.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If corner portion of semiconductor material is retained during backside removal, then source/drain features are protected, but additional material must be removed later

Engineering Contradiction:

Improvesource/drain feature protectionVSAvoidprocessing steps

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The corner portion serves a dual function: it protects the source/drain features during backside removal, and then it is automatically removed in the same etch process that forms the backside contact recesses. The etch process that removes the bulk semiconductor material also removes the corner portion, eliminating the need for separate removal steps.

Inventive Principle:

Principle #25Self-service

3Reliability

If source/drain features are formed with convex surface to increase volume, then device performance improves, but processing precision requirements increase

Engineering Contradiction:

Improvedevice performanceVSAvoidconvex surface formation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The etch selectivity parameters are optimized to create the desired convex surface profile on the source/drain features. By controlling the etch rate and selectivity ratios between different materials, the process naturally forms the convex shape that increases device volume and performance without requiring additional precision steps.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12347775B2Semiconductor devices with backside power rail and methods of fabrication thereof

Publication Date: 2025.07.01 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Corner portions of a semiconductor fin are kept on the device while removing a semiconductor fin prior to forming a backside contact. The corner portions of the semiconductor fin protect source/drain regions from etchant during backside processing. The corner portions allow the source/drain features to be formed with a convex profile on the backside. The convex profile increases volume of the source/drain features, thus, improving device performance. The convex profile also increases processing window of backside contact recess formation.