Germanium Fin S/D Boron Diffusion via Thermal Mixing

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Solution Overview

Problem

Current technologies face challenges in forming abrupt junctions for p-type FinFETs with high germanium content fins, as boron diffusion is reduced with increasing germanium content, making it impractical for advanced technology nodes, especially at the 10 nanometer technology node and beyond.

Innovation Solution

A method involving forming a germanium-including fin with a dummy gate, growing an in-situ p-type doped silicon germanium layer over the source/drain region, and annealing to thermally mix and diffuse the p-type dopant into the source/drain region, creating a source/drain extension adjacent to the channel with a higher germanium concentration under the gate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high germanium content is used in the fin channel to improve hole mobility, then device performance is improved, but boron diffusion into the source/drain region is significantly reduced

Engineering Contradiction:

Improvehole mobilityVSAvoidboron diffusion

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the germanium concentration parameter spatially within the fin structure. The channel region maintains high germanium content (75-100%) for optimal hole mobility, while the source/drain regions have reduced germanium content (0-60%) to enable effective boron diffusion. This parameter gradient is achieved through selective epitaxial growth and thermal mixing processes that redistribute germanium atoms during annealing.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If ion implantation is used to implant boron into the epitaxy layer, then source/drain extensions can be formed, but the process becomes impractical due to tight dimensions and three-dimensional structures

Engineering Contradiction:

Improveboron implantation feasibilityVSAvoidjunction abruptness

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent replaces the mechanical ion implantation process with a thermal diffusion process. Instead of physically implanting boron ions through masks and acceleration fields, the invention uses in-situ doped epitaxial layers followed by thermal annealing to diffuse boron atoms into the source/drain regions. This substitution eliminates the complexity of aligning ion implantation equipment with three-dimensional FinFET structures while achieving comparable or superior junction profiles.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent incorporates boron doping during the epitaxial growth step before the annealing process. By pre-doping the epitaxial layer with boron at controlled concentrations, the subsequent thermal annealing step can efficiently diffuse the boron into the source/drain regions without requiring complex in-situ doping during annealing. This preliminary doping action simplifies the overall process sequence.

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 enhances p-type FinFET performance by achieving a sharp source/drain extension border within the channel, optimizing hole mobility while maintaining a high germanium concentration, thus addressing the limitations of boron diffusion in high germanium content fins.

Implementation Method 1

annealing to thermally mix the germanium of the in-situ p-type doped silicon germanium layer and the germanium of the germanium-including fin in the source/drain region

Methodology Applied

Scientific EffectThermal mixing: Diffusion

Implementation Method 2

diffuse the p-type dopant of the in-situ p-type doped silicon germanium layer into the source/drain region of the germanium-including fin

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS9634142B1Method for improving boron diffusion in a germanium-rich fin through germanium concentration reduction in fin S/D regions by thermal mixing

Publication Date: 2017.04.25 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method may include forming a germanium-including fin on a substrate, and forming a dummy gate extending over the germanium-including fin, creating a channel under the gate and a source/drain region of the germanium-including fin extending from under the dummy gate on each side of the dummy gate. An in-situ p-type doped silicon germanium layer may be grown over the source/drain region, the germanium-including fin having a higher concentration of germanium than the in-situ p-type doped silicon germanium layer. An anneal thermally mixes the germanium of the in-situ p-type doped silicon germanium layer and the germanium of the germanium-including fin in the source/drain region of the germanium-including fin and diffuses the p-type dopant of the in-situ p-type doped silicon germanium layer into the channel of the germanium-including fin, forming a source/drain extension. A portion of the channel has a higher germanium concentration than the source/drain region.