Bipolar Transistor Air Gap Shallow Trench Isolation
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Solution Overview
Problem
Current bipolar junction transistor (BJT) device structures and fabrication methods do not adequately enhance performance for high-frequency and high-power applications, particularly in RFICs and BiCMOS integrated circuits, due to limitations in isolation and stress management.
Innovation Solution
The method involves forming a trench isolation region in a substrate coextensive with the collector, creating a base layer on the collector with a dielectric layer on top, and partially removing the trench isolation region to define an air gap beneath the base layer, which introduces mechanical stress and reduces parasitic capacitance through strain engineering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench isolation region is formed coextensive with the collector to provide isolation, then isolation performance is improved, but parasitic capacitance between collector and base increases
Solution Approach 1:
The patent extracts the harmful dielectric material from the trench isolation region beneath the base layer, removing the source of parasitic capacitance while preserving the isolation function. The air gap created by removing the dielectric material eliminates the capacitive coupling between collector and base, directly resolving the contradiction between isolation performance and parasitic capacitance reduction.
Solution Approach 2:
The patent introduces an air gap (porous space) within the trench isolation region to replace the solid dielectric material. This porous structure beneath the base layer reduces the dielectric constant in the critical region, thereby reducing parasitic capacitance while maintaining the isolation function through the remaining dielectric material at the trench periphery.
2Productivity
If strain engineering is implemented to enhance carrier mobility, then device performance is improved, but device structure complexity increases
Solution Approach 1:
The patent changes the physical state of the trench isolation region by creating an air gap, which introduces mechanical stress/strain in the semiconductor layers. This parameter change (introducing strain) enhances carrier mobility in the base layer without requiring complex additional structures, as the strain is naturally induced by the air gap geometry.
3Object-generated harmful factors
If the trench isolation region is partially removed to create an air gap, then parasitic capacitance is reduced, but manufacturing process complexity increases
Solution Approach 1:
The patent performs the dielectric removal action after forming the base layer and dielectric layer, but plans the air gap creation as part of the isolation structure formation process. This preliminary planning of the air gap location and extent allows for controlled removal of dielectric material through the openings, making the manufacturing process manageable despite the additional step.
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 improves device performance by reducing collector-to-base parasitic capacitance and allowing for strain-induced enhancements in carrier mobility, thereby optimizing the BJT's operational characteristics for high-frequency and high-power applications.
Implementation Method 1
reducing collector-to-base parasitic capacitance
Implementation Method 2
allowing for strain-induced enhancements in carrier mobility
Data Source
AI summary
Device structures, fabrication methods, and design structures for a bipolar junction transistor. A trench isolation region is formed in a substrate. The trench isolation region is coextensive with a collector in the substrate. A base layer is formed on the collector and on a first portion of the trench isolation region. A dielectric layer is formed on the base layer and on a second portion of the trench isolation region peripheral to the base layer. After the dielectric layer is formed, the trench isolation region is at least partially removed to define an air gap beneath the dielectric layer and the base layer.