Epitaxial Source/Drain Layers That Block Phosphorus Channel Diffusion

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Solution Overview

Problem

As transistors scale to smaller dimensions, maintaining suitable contact resistivity of the source/drain region becomes challenging, with phosphorus diffusion into the channel leading to increased leakage and degradation of short channel effects, while arsenic, used to alleviate this, is toxic and expensive and results in higher resistance.

Innovation Solution

A highly conformal and selective epitaxial antimony doped silicon nucleation layer is used, either alone or co-doped with phosphorus, to suppress phosphorus diffusion and improve conductivity, achieving low resistivity and superior short channel effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If phosphorus is used to improve conductivity in the source/drain region, then electrical conductance increases, but phosphorus diffuses into the channel causing increased leakage and degradation of short channel effects

Engineering Contradiction:

Improvecontact resistivityVSAvoidphosphorus diffusion into channel

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

An antimony-doped silicon nucleation layer is introduced as an intermediary between the phosphorus-doped main layer and the channel. This nucleation layer acts as a diffusion barrier that prevents phosphorus from migrating into the channel while maintaining electrical conductivity. The antimony doping concentration (1E19 to 1E21 atoms/cm³) is optimized to provide both barrier properties and conductive pathways.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The source/drain region is segmented into two distinct layers: a nucleation layer containing antimony and silicon, and a main layer containing phosphorus and silicon. This segmentation allows each layer to perform its specialized function - the nucleation layer provides diffusion blocking and initial conduction, while the main layer provides bulk conduction - thereby resolving the contradiction between preventing phosphorus diffusion and maintaining overall conductivity.

Inventive Principle:

Principle #1Segmentation

2Object-generated harmful factors

If arsenic is used to suppress phosphorus diffusion, then diffusion blocking improves, but resistance increases and toxicity and handling difficulty increase

Engineering Contradiction:

Improvephosphorus diffusion blockingVSAvoidsource/drain resistance

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The invention changes the dopant parameter from arsenic to antimony in the nucleation layer. Antimony provides similar diffusion blocking capabilities to arsenic but with superior electrical conductivity properties. The dopant concentration is precisely controlled at 1E19 to 1E21 atoms/cm³ to optimize the balance between diffusion blocking and electrical conduction, avoiding the high resistance associated with arsenic doping.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Antimony is selected as a replacement for arsenic because it is less toxic and easier to handle, while providing comparable or superior performance. The nucleation layer is designed to be a thin film (2-10 nm) that can be precisely controlled during fabrication, making the process more reliable and less hazardous than arsenic-based approaches.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Productivity

If transistor dimensions are scaled down, then device density increases, but contact resistance increases due to smaller contact area

Engineering Contradiction:

Improvedevice densityVSAvoidcontact resistance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The nucleation layer is selectively formed only in the source/drain regions adjacent to the channel, providing localized diffusion blocking and conductivity enhancement exactly where needed. This local application of the antimony-doped layer ensures that contact resistance is optimized at the critical metal-semiconductor interface without affecting other regions of the transistor, thereby maintaining high device density while improving contact properties.

Inventive Principle:

Principle #3Local quality

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 antimony doped silicon nucleation layer effectively blocks phosphorus diffusion, achieving low source/drain contact resistivity and improved transistor performance without the toxicity and cost issues associated with arsenic.

Implementation Method 1

phosphorus diffusion into the channel

Methodology Applied

Scientific EffectPhosphorus diffusion: Diffusion

Implementation Method 2

antimony doped silicon nucleation layer

Methodology Applied

Scientific EffectDoping: Dopants

Implementation Method 3

highly conformal and selective epitaxial antimony doped silicon nucleation layer

Methodology Applied

Scientific EffectEpitaxy: Epitaxy

Data Source

PatentUS20250006790A1Transistors with antimony and phosphorus doped epitaxial source/drain layers

Publication Date: 2025.01.02 INTEL CORP

AI summary

In some implementations, a device may include a channel material. In addition, the device may include a contact metal. The device may include a first layer between the channel material and the contact metal, the first layer having antimony and silicon. Moreover, the device may include a second layer between the contact metal and the first layer, the second layer having phosphorus and silicon.