Germanium Extrinsics Base HBT Sacrificial Post

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Solution Overview

Problem

Conventional bipolar transistors face challenges in scaling down due to limitations in reducing parasitic extrinsic base resistance and extrinsic base-collector capacitance, particularly with silicon-based raised base techniques, which increase manufacturing costs and require high temperature processing.

Innovation Solution

The use of a germanium extrinsic base with a sacrificial emitter post in heterojunction bipolar transistors, allowing for reduced extrinsic base resistance and lower process temperatures, while maintaining or improving device performance through increased etchant selectivity and simplified fabrication processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If silicon-based raised base techniques are used to reduce extrinsic base-collector capacitance, then device performance is improved, but manufacturing cost increases and high temperature processing is required

Engineering Contradiction:

Improvedevice performanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the material parameter from silicon to germanium for the extrinsic base region. Germanium has higher etchant selectivity and lower melting point, enabling fabrication at reduced temperatures while maintaining the raised base structure's performance benefits of low extrinsic base-collector capacitance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a sacrificial emitter post made of germanium that is temporarily present during fabrication and then completely removed. This disposable structure enables the formation of the germanium extrinsic base through selective etching, simplifying the manufacturing process and reducing costs by eliminating complex high temperature processing steps

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If silicon-based raised base techniques are used to reduce extrinsic base-collector capacitance, then device performance is improved, but process temperature must be increased

Engineering Contradiction:

Improvedevice performanceVSAvoidprocess temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent utilizes the phase transition properties of germanium, which has a lower melting point than silicon. This allows the germanium extrinsic base to be formed and processed at lower temperatures through controlled melting and solidification, eliminating the need for high temperature processing required by silicon-based approaches

Inventive Principle:

Principle #36Phase transitions

3Reliability

If conventional silicon raised base fabrication is used, then extrinsic base resistance is reduced, but etchant selectivity is poor

Engineering Contradiction:

Improveextrinsic base resistanceVSAvoidetchant selectivity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the material parameter from silicon to germanium for the extrinsic base region. Germanium exhibits significantly higher etchant selectivity compared to silicon, allowing for precise patterning and formation of the raised base structure without requiring excessive etching power that would compromise surrounding structures

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a sacrificial emitter post as an intermediary structure that facilitates the formation of the germanium extrinsic base. This temporary structure enables selective etching processes to work effectively by providing a defined starting point and protecting other regions during fabrication

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enables the fabrication of smaller bipolar transistors with reduced costs and improved performance by utilizing the higher conductivity of germanium and lower melting point compared to silicon, while maintaining device integrity and efficiency.

Implementation Method 1

depositing a germanium layer on a SiGe layer to form an extrinsic base region

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Implementation Method 2

depositing a germanium layer on a SiGe layer to form an extrinsic base region

Methodology Applied

Scientific EffectChemical Vapour Deposition: Chemical Vapour Deposition

Implementation Method 3

utilizing the higher conductivity of germanium and lower melting point compared to silicon, while maintaining device integrity and efficiency

Methodology Applied

Scientific EffectSelective Etching:

Data Source

PatentUS9064886B2Heterojunction bipolar transistor having a germanium extrinsic base utilizing a sacrificial emitter post

Publication Date: 2015.06.23 NEWPORT FAB LLC

AI summary

Disclosed is a method for fabricating a heterojunction bipolar transistor (“HBT”), and the resulting structure. The method includes forming a germanium layer over a SiGe layer, the SiGe layer including an intrinsic base. Thereafter, an emitter sacrificial post and a raised germanium extrinsic base are formed by etching away portions of the germanium layer. Then, a conformal dielectric layer is deposited over the raised germanium extrinsic base. The process continues by removing the emitter sacrificial post and forming an emitter over the intrinsic base within an emitter opening defined by the previous removal of the emitter sacrificial post. The resulting structure has a raised germanium extrinsic base with a reduced parasitic base-collector capacitance.