Graded SiGe FinFET Source/Drain Structure for Lower Leakage

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Solution Overview

Problem

As the minimum feature sizes in semiconductor devices are reduced, challenges arise in reducing leakage current and increasing the turn-on current of FinFETs, particularly due to dopant diffusion and the need for deeper source/drain recesses.

Innovation Solution

The formation of epitaxial source/drain regions with a bottom layer of silicon germanium doped with boron, which reduces dopant diffusion and allows for a deeper source/drain recess, increasing the volume of the epitaxial source/drain regions and enhancing the turn-on current of FinFETs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the minimum feature size is reduced to increase integration density, then more components can be integrated into a given area, but leakage current increases and turn-on current decreases

Engineering Contradiction:

Improveintegration densityVSAvoidleakage current

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies local quality by creating a multi-layered source/drain structure with different materials and doping concentrations in specific regions. The epitaxial semiconductor material with graded doping concentration is placed locally in the source/drain regions to reduce leakage current, while maintaining high integration density through optimized feature dimensions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses composite materials by combining the epitaxial semiconductor material with the underlying substrate material in a layered structure. This composite approach allows optimization of electrical properties in the source/drain regions while maintaining the overall device structure for high integration density.

Inventive Principle:

Principle #40Composite materials

2Power

If dopant concentration is increased to increase turn-on current, then more current flows when the device is on, but dopant diffusion increases causing leakage current

Engineering Contradiction:

Improveturn-on currentVSAvoiddopant diffusion

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent applies parameter changes by using a graded doping concentration profile in the epitaxial semiconductor material. The doping concentration varies spatially within the source/drain regions, allowing high turn-on current where needed while reducing dopant diffusion to adjacent regions, thereby minimizing leakage current.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The epitaxial semiconductor material acts as an intermediary layer between the heavily doped source/drain regions and the substrate. This intermediate layer with controlled doping concentration prevents excessive dopant diffusion into the substrate while maintaining high turn-on current in the source/drain regions.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If source/drain recess depth is increased to reduce leakage current, then leakage is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improveleakage currentVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by forming the epitaxial semiconductor material in the source/drain regions before final doping and metallization steps. This preliminary structure formation allows controlled doping profiles to be established, reducing leakage current while simplifying subsequent manufacturing steps compared to forming deeper recesses.

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 reduces leakage current by blocking dopant diffusion and increases the turn-on current of FinFETs by up to 10% while maintaining reduced leakage, thereby improving the overall electrical performance of FinFETs.

Implementation Method 1

reduces dopant diffusion

Methodology Applied

Scientific EffectDopant diffusion: Diffusion

Implementation Method 2

epitaxially growing semiconductor material on sidewalls of the recess

Methodology Applied

Scientific EffectEpitaxial growth: Epitaxy

Data Source

PatentUS12218240B2Source/drain regions of FinFET devices and methods of forming same

Publication Date: 2025.02.04 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method includes forming a semiconductor fin over a substrate, etching the semiconductor fin to form a recess, wherein the recess extends into the substrate, and forming a source/drain region in the recess, wherein forming the source/drain region includes epitaxially growing a first semiconductor material on sidewalls of the recess, wherein the first semiconductor material includes silicon germanium, wherein the first semiconductor material has a first germanium concentration from 10 to 40 atomic percent, epitaxially growing a second semiconductor material over the first semiconductor material, the second semiconductor material including silicon germanium, wherein the second semiconductor material has a second germanium concentration that is greater than the first germanium concentration, and epitaxially growing a third semiconductor material over the second semiconductor material, the third semiconductor material including silicon germanium, wherein the third semiconductor material has a third germanium concentration that is smaller than the second germanium concentration.