SiGe HBT Extrinsic Base Graphene Formation for Lower Base Resistance
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Solution Overview
Problem
The base resistance of SiGe heterojunction bipolar transistors (HBTs) is a critical factor limiting their performance at high operation frequencies, and existing technologies have not effectively addressed this issue.
Innovation Solution
The method involves doping epitaxial silicon with carbon (C) and boron (B) in situ, along with a metal catalyst, followed by plasma treatment and laser annealing to form highly conductive graphene regions in the extrinsic base region of the HBT, reducing base resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SiGe HBT structure is used, then device fabrication is straightforward, but base resistance is high which limits high-frequency performance
Solution Approach 1:
The patent changes the material composition and doping parameters of the extrinsic base region by incorporating carbon-doped silicon-germanium (SiGe) with specific carbon concentrations (5-20 atomic percent) and germanium concentrations (10-30 atomic percent). This parameter change transforms the electrical properties of the base region, reducing base resistance by forming highly conductive regions that enable high-frequency operation while maintaining manufacturability through controlled epitaxial growth and ion implantation processes.
Solution Approach 2:
The patent employs composite material structure by integrating carbon-doped SiGe layers within the silicon-based HBT architecture. The extrinsic base region consists of a composite of silicon, germanium, and carbon elements, where carbon doping creates graphitic structures that provide low-resistance pathways. This composite approach combines the benefits of silicon compatibility with the high conductivity of carbon-doped regions, resolving the contradiction between ease of manufacture and high-frequency performance.
2Speed
If base width is reduced to improve frequency response, then high-frequency performance improves, but base resistance increases
Solution Approach 1:
The patent applies local quality by creating regions with different material compositions within the base structure. The extrinsic base region has localized carbon-doped SiGe sections with high conductivity embedded within the broader base structure. This allows the base width to be reduced for improved frequency response while the localized carbon-doped regions maintain low base resistance through their inherently higher conductivity, decoupling the trade-off between speed and resistance.
Solution Approach 2:
The patent changes the doping concentration parameters locally in the extrinsic base region. By increasing carbon concentration (5-20 atomic percent) and germanium concentration (10-30 atomic percent) specifically in the extrinsic base region, the material achieves higher carrier concentration and mobility. This parameter change allows the region to maintain low resistance even when the overall base width is reduced, thereby improving frequency response without sacrificing conductivity.
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 significantly enhances the performance of SiGe HBTs at high operation frequencies by reducing base resistance, making them more suitable for high-frequency applications.
Implementation Method 1
doping carbon (C) and boron (B) in situ to the silicon layer
Implementation Method 2
conducting a plasma treatment to the doped silicon layer
Implementation Method 3
conducting a laser annealing to the doped silicon layer
Implementation Method 4
graphene regions are formed in the silicon epitaxial layer
Data Source
AI summary
The present application provides methods for manufacturing BiCMOS device and the heterojunction bipolar transistor (HBT) contained therein. In formation of a raised extrinsic base region of the heterojunction bipolar transistor, the epitaxial silicon is doped with carbon (C) and boron (B) in situ and is doped with a metal catalyst simultaneously, then, the plasma treatment and the laser annealing are conducted to the carbon, and a graphene region is formed in the Si epitaxial layer. Because of high conductivity of graphene, the base resistance of the SiGe HBT can be reduced to enhance its radiation performance. The above method can be applied to conventional BiCMOS device process by performing plasma treatment and laser annealing to the doped carbon to form the graphene region in the extrinsic base region. The method is easily controlled and integrated into conventional BiCMOS device process.