Bipolar Transistor Polysilicon Base Terminal RF Performance
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Solution Overview
Problem
Conventional bipolar transistor integration schemes face challenges with high defectivity in the base-collector junction, increased parasitic capacitance, and stack height, which affect the yield and performance of heterojunction bipolar transistors (HBTs).
Innovation Solution
A bipolar transistor structure is developed with a polysilicon base terminal that is laterally electrically contacting the base region, epitaxially grown silicon, and a reduced parasitic base-collector capacitance, integrated in a BiCMOS technology that combines CMOS and HBTs on a single die, using a self-aligned integration scheme and a special base window geometry to alleviate processing complexities and enhance RF properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bipolar transistor integration schemes are used, then HBTs can be manufactured, but defectivity in the base-collector junction increases and manufacturing yield decreases
Solution Approach 1:
A polysilicon base terminal is formed in advance before the base region is grown. This preliminary structure serves as a template that guides the epitaxial growth of the base region, ensuring proper alignment and reducing defects at the base-collector junction interface. The base terminal is prepared beforehand to prevent misalignment and interface defects during subsequent processing steps.
Solution Approach 2:
The polysilicon base terminal acts as an intermediary structure between the collector region and the base region. It provides a controlled interface that mediates the formation of the base-collector junction, reducing direct contact between mismatched materials and minimizing defect generation at the heterojunction interface.
2Reliability
If conventional integration schemes are used, then bipolar transistors can be manufactured, but parasitic base-collector capacitance increases and RF performance deteriorates
Solution Approach 1:
The base terminal is extracted from the traditional vertical configuration and repositioned to laterally contact the base region. This separation removes the direct vertical overlap between the base terminal and collector region, thereby extracting the parasitic capacitance pathway and reducing base-collector capacitance to improve RF performance.
Solution Approach 2:
The base terminal contact is transitioned from a vertical arrangement to a lateral configuration. By changing the dimensional arrangement from vertical overlap to lateral contact, the parasitic capacitance between the base terminal and collector is significantly reduced, enhancing high-frequency performance.
3Productivity
If conventional integration schemes are used, then manufacturing can proceed, but stack height increases and integration density decreases
Solution Approach 1:
The base terminal contact is reconfigured from a vertical stack arrangement to a lateral contact arrangement. This dimensional change reduces the vertical stack height by eliminating the need for thick base terminal layers stacked above the collector, thereby increasing integration density.
Solution Approach 2:
The base terminal function is segmented into a separate lateral contact structure rather than being integrated vertically with the collector and base regions. This segmentation allows independent optimization of each component's position and reduces overall stack height while maintaining electrical functionality.
4Ease of manufacture
If conventional integration schemes are used, then processing can be completed, but processing complexity increases and manufacturing becomes more difficult
Solution Approach 1:
The polysilicon base terminal structure serves a dual function: it acts as both the base contact and as a template that guides the epitaxial growth of the base region. This self-service approach eliminates the need for separate alignment and positioning steps, simplifying the manufacturing process.
Solution Approach 2:
The base terminal formation and base region alignment functions are merged into a single structural element. The polysilicon base terminal simultaneously provides electrical contact and defines the base region geometry, combining multiple functions into one structure to reduce processing steps.
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 reduces defectivity, minimizes parasitic capacitance, and allows for easier integration of HBTs with CMOS, improving yield and performance by enabling further node shrinking and enhancing RF properties.
Implementation Method 1
a base terminal laterally electrically contacting the base region, wherein the base terminal includes polysilicon
Implementation Method 2
epitaxially grown silicon
Data Source
AI summary
According to various embodiments, a bipolar transistor structure may include: a substrate; a collector region in the substrate; a base region disposed over the collector region, an emitter region disposed over the base region; a base terminal laterally electrically contacting the base region, wherein the base terminal includes polysilicon.