Backside Base Contact Layout for Stable BJT Base Potential

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Solution Overview

Problem

Implementing backside interconnects for bipolar junction transistors (BJTs) poses challenges due to the importance of base potential control for performance, especially as semiconductor devices with backside interconnects become more prevalent.

Innovation Solution

A semiconductor device with a backside base contact is fabricated by partially removing the substrate layer under the base terminal, using a dielectric barrier to protect underlying structures, and forming a continuous backside contact that extends laterally beneath the emitter and collector terminals, enhancing base potential consistency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If backside interconnects are implemented for BJTs, then layout flexibility is improved, but base potential control deteriorates

Engineering Contradiction:

Improvelayout flexibilityVSAvoidbase potential control

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The base contact is segmented into two parts: a frontside contact region and a backside contact region. The backside contact is divided into multiple discrete contact points (first backside contact, second backside contact) rather than a single continuous contact, allowing independent control of different base regions while maintaining overall base potential stability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The base contact is extended from the traditional single-sided (frontside only) approach to a dual-sided approach by adding backside contacts. This dimensional change allows the base to be contacted from both the front surface and the back surface of the semiconductor substrate, providing additional degrees of freedom for potential control while maintaining layout flexibility

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Adaptability or versatility

If substrate is removed under base terminal for backside contact, then backside base contact is achieved, but device robustness deteriorates

Engineering Contradiction:

Improvebackside contact capabilityVSAvoiddevice robustness

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The substrate removal is applied locally and selectively only in specific regions where backside contacts are needed, rather than removing the entire substrate. The first and second backside contacts are formed in separate localized areas under the base terminal, allowing backside contact functionality while preserving substrate support in other critical regions

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of completely removing the substrate under the base terminal (which would compromise robustness), the invention applies partial substrate removal - just enough to expose the base region for backside contact formation while leaving sufficient substrate material to maintain structural integrity and mechanical support

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS20250393272A1BJT with backside base contact

Publication Date: 2025.12.25 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

Semiconductor devices include a semiconductor well layer having a first dopant polarity. A collector terminal is on a top surface of the semiconductor well layer, having a second dopant polarity. An emitter terminal is on the top surface of the semiconductor well layer, having the second dopant polarity. A conductor contacts a bottom surface of the semiconductor well layer and extends laterally below the collector terminal and the emitter terminal.