SiGe HBT Lateral Trenches Reduce Collector-Base Capacitance
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Solution Overview
Problem
Silicon-germanium heterojunction bipolar transistors (SiGe HBTs) face parasitic effects such as collector-substrate and collector-base capacitances, which hinder their high-frequency performance.
Innovation Solution
The SiGe HBT structure incorporates isolation and lateral trenches filled with oxide film, along with a SiGe base layer comprising intrinsic and extrinsic regions, to reduce collector-base capacitance, achieved through a manufacturing method involving ion implantation, trench formation, and epitaxial deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional SiGe HBT structure is used, then device integration and manufacturing compatibility are improved, but collector-base capacitance increases which degrades high-frequency performance
Solution Approach 1:
The base region is segmented into intrinsic base region and extrinsic base region. The intrinsic base region is positioned at the bottom of the emitter window where it directly interfaces with the collector, while the extrinsic base region is positioned elsewhere. This segmentation allows the intrinsic region to provide low-capacitance interface while the extrinsic region provides standard electrical functionality, thereby reducing overall collector-base capacitance while maintaining manufacturing compatibility
Solution Approach 2:
Lateral trenches are introduced as a new structural dimension extending horizontally from the isolation trenches into the collector region. These lateral trenches create additional spatial separation between the collector and base regions, reducing the overlapping area and thus the collector-base capacitance. This dimensional approach maintains compatibility with existing vertical device architecture while adding capacitance reduction capability
2Object-affected harmful factors
If collector-base capacitance is reduced through structural modifications, then high-frequency performance is improved, but device structure complexity increases
Solution Approach 1:
The oxide film filling is applied selectively only in specific regions (lateral trenches and isolation trenches) rather than throughout the entire device structure. This localized application reduces collector-base capacitance in critical areas while minimizing the overall structural complexity and material usage. The local quality modification allows capacitance reduction without requiring complete structural redesign
Solution Approach 2:
The lateral trenches are nested within the collector region and connected to the isolation trenches, creating a hierarchical structure where smaller features are integrated into larger structural elements. This nesting approach reduces collector-base capacitance through the lateral trenches while utilizing the existing isolation trench infrastructure, thereby limiting the increase in overall device complexity
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 effectively reduces collector-base capacitance, enhancing the high-frequency performance of SiGe HBTs by utilizing cavities or oxide-filled trenches instead of ordinary silicon, thereby improving device characteristics.
Implementation Method 1
The lateral trenches are filled with a certain amount of oxide film, and are not fully filled with the oxide film; or the lateral trenches are fully filled with the oxide film
Implementation Method 2
1) performing ion implantation to predetermined implantation regions in a on substrate
Implementation Method 3
10) depositing a first dielectric film and forming a base window in the first dielectric film, and performing epitaxial deposition of a base SiGe film
Data Source
AI summary
A SiGe HBT having low collector-base capacitance is disclosed, which includes: a silicon substrate, including isolation trenches, a collector region situated between the isolation trenches, and lateral trenches; a SiGe base layer formed on the silicon substrate; and an emitter region formed on the SiGe base layer. Each lateral trench is situated in the collector region on one side of an isolation trench, and is connected to the isolation trench. Moreover, a manufacturing method of a SiGe HBT having low collector-base capacitance is disclosed, which includes: performing ion implantation to predetermined regions in a silicon substrate before trench isolations are formed; forming lateral trenches by etching ion implantation regions after the trench isolations are formed; then forming a SiGe HBT device by an ordinary semiconductor process. The present invention can reduce the collector-base capacitance and therefore improve high-frequency characteristics of the device.