Buried Trap-Rich Isolation in HBTs for High Breakdown Voltage

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Solution Overview

Problem

Increasing the breakdown voltage of heterojunction bipolar transistors (HBTs) without degrading their RF performance is challenging, particularly in Si/SiGe HBTs used in power amplifier applications.

Innovation Solution

A buried trap rich isolation region is embedded within the bulk substrate, separated from the sub-collector region by a layer of the bulk substrate, using polycrystalline semiconductor material, and deep trench isolation structures to reduce substrate leakage and collector-to-subcollector capacitance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the breakdown voltage of HBT is increased, then the power amplifier performance is improved, but the RF performance degrades

Engineering Contradiction:

Improvebreakdown voltageVSAvoidRF performance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The collector region is segmented into a sub-collector region and a main collector region, separated by the trap-rich isolation region. This segmentation allows the sub-collector to handle high voltage stress while the main collector maintains RF performance, resolving the contradiction between breakdown voltage and RF performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A trap-rich isolation region is introduced as an intermediary layer between the sub-collector and the substrate. This intermediary region reduces substrate leakage and isolates electric fields, enabling high breakdown voltage without degrading RF performance by mediating the interaction between the sub-collector and substrate.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If deep trench isolation structures are used, then device-to-device isolation is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvedevice-to-device isolationVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The trap-rich isolation region is merged with the shallow trench isolation structure, combining two isolation functions into a single integrated structure. This reduces manufacturing steps compared to implementing deep trench isolation separately, while achieving superior device-to-device isolation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The isolation region is engineered with specific trap density parameters and depth characteristics that provide enhanced isolation performance. By optimizing these parameters, the structure achieves deep isolation effects with moderate manufacturing complexity, avoiding the need for extremely deep trenches.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12170313B2Heterojunction bipolar transistor with buried trap rich isolation region

Publication Date: 2024.12.17 GLOBALFOUNDRIES US INC

AI summary

The present disclosure relates to semiconductor structures and, more particularly, to heterojunction bipolar transistors (HBTs) with a buried trap rich region and methods of manufacture. The structure includes: a trap rich isolation region embedded within the bulk substrate; and a heterojunction bipolar transistor above the trap rich isolation region, with its sub-collector region separated by the trap rich isolation region by a layer of the bulk substrate.