Self-Aligned Bipolar Transistor Emitter Base Fabrication

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Solution Overview

Problem

Conventional bipolar junction transistors (HBTs) face challenges in enhancing device performance and fabrication methods for BiCMOS integrated circuits, particularly in achieving self-aligned emitter and base structures for improved high-frequency and high-power efficiency applications.

Innovation Solution

A method involving the formation of an intrinsic base layer, a sacrificial mandrel, and an extrinsic base layer, where the extrinsic base is self-aligned using spacers, and an emitter is formed in a window defined by partial removal of the mandrel, with selective epitaxial growth and silicide layer formation to enhance base contact and reduce resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional fabrication methods are used for HBTs, then the manufacturing process is simpler, but the device performance and base resistance are not optimized

Engineering Contradiction:

Improvedevice performanceVSAvoidfabrication process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The base layer is divided into intrinsic base layer and extrinsic base layer, with the extrinsic base layer further segmented into multiple sections (first sections and second sections) of varying thicknesses. This segmentation allows optimization of base resistance and current distribution while maintaining manufacturing feasibility through selective epitaxial growth.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A sacrificial mandrel is formed on the intrinsic base layer before growing the extrinsic base layer. The mandrel serves as a preliminary structure that defines the emitter window location and guides the self-aligned formation of the extrinsic base, ensuring proper alignment without requiring complex subsequent alignment steps.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 3:

The sacrificial mandrel acts as an intermediary structure during fabrication. It is formed temporarily to enable self-aligned growth of the extrinsic base layer, then partially removed to create the emitter window. This intermediary structure simplifies the overall process by eliminating the need for precise alignment steps.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the extrinsic base layer is made uniform in thickness, then the manufacturing process is simpler, but the base resistance and device performance are not optimized

Engineering Contradiction:

Improvebase resistanceVSAvoidextrinsic base layer uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The extrinsic base layer is designed with different thicknesses in different regions: first sections with a first thickness and second sections with a second thickness. This local variation in quality allows optimization of base resistance and current distribution in specific areas while maintaining overall manufacturing feasibility through selective epitaxial growth processes.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If the emitter window is defined by complete removal of the mandrel, then the emitter formation is simpler, but the alignment between emitter and extrinsic base is not precise

Engineering Contradiction:

Improveemitter alignmentVSAvoidemitter window formation

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The sacrificial mandrel is partially removed rather than completely removed to define the emitter window. This partial removal strategy maintains the mandrel structure in areas where it provides alignment guidance for the extrinsic base, while creating the necessary opening for emitter formation. The remaining mandrel portions continue to serve as alignment references, ensuring precise emitter-to-base alignment.

Inventive Principle:

Principle #16Partial or excessive 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 results in improved device performance by reducing base resistance and enhancing the uniformity and planarity of the extrinsic base layer, leading to increased speed and efficiency in bipolar junction transistors, suitable for high-frequency and high-power applications.

Implementation Method 1

forming an extrinsic base layer on the top surface of the intrinsic base layer. The extrinsic base layer is self-aligned with the sacrificial mandrel

Methodology Applied

Scientific EffectSelective epitaxial growth: Epitaxy

Implementation Method 2

with selective epitaxial growth and silicide layer formation to enhance base contact and reduce resistance

Methodology Applied

Scientific EffectSilicide formation: Deposition (physical)

Data Source

PatentUS8710500B2Bipolar junction transistor with a self-aligned emitter and base

Publication Date: 2014.04.29 GLOBALFOUNDRIES US INC

AI summary

Methods for fabricating bipolar junction transistors with self-aligned emitter and extrinsic base, bipolar junction transistors made by the methods, and design structures for a BiCMOS integrated circuit. The bipolar junction transistor is fabricated using a sacrificial emitter pedestal that provides a sacrificial mandrel promoting self-alignment between the emitter and the extrinsic base. The sacrificial emitter pedestal is subsequently removed to open an emitter window extending to the intrinsic base. An emitter is formed in the emitter window that lands on the intrinsic base.