Heterojunction Bipolar Transistors With Recessed SiGe Base
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Solution Overview
Problem
High performance heterojunction bipolar transistors (HBTs) are limited by high collector-base capacitance, parasitic resistances, and broad SiGe base dopant profiles, which are constrained by thermal budgets and downstream processes in BiCMOS technologies, hindering sharp dopant profiles and optimal RF performance.
Innovation Solution
The structure and method involve forming a recessed SiGe base with selective epitaxial regrowth, a lateral intrinsic base, and extrinsic base connection, along with spacers to define an emitter region, achieving a sharper dopant profile and reduced capacitance through precise control of recess depth and dopant distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional HBT structures are used with standard doping processes, then manufacturing is simpler, but dopant profiles are broad and capacitance is high
Solution Approach 1:
The base region is segmented into two distinct parts: an intrinsic base region formed by selective epitaxial regrowth in a recess, and an extrinsic base region formed by doped material. This segmentation allows the intrinsic region to provide sharp dopant profiles while the extrinsic region provides electrical connection, resolving the contradiction between profile sharpness and structural complexity.
Solution Approach 2:
The invention introduces a vertical dimension by forming a recess in the collector region and filling it with intrinsic base material through selective epitaxial regrowth. This three-dimensional structure enables sharp dopant profiles at the interface while maintaining overall device functionality, transforming a two-dimensional doping problem into a three-dimensional structural solution.
2Quantity of substance
If scaling is used to reduce total capacitance, then capacitance decreases, but parasitic resistances increase
Solution Approach 1:
The extrinsic base region is specifically doped to provide low resistance pathways for electrical connection, while the intrinsic base region maintains sharp dopant profiles. This local differentiation of material properties allows the device to achieve low parasitic resistance in the extrinsic region while maintaining low capacitance through overall scaling, resolving the contradiction between capacitance reduction and resistance control.
3Manufacturing precision
If thermal budgets are increased to improve dopant distribution, then dopant profiles improve, but downstream processes are constrained
Solution Approach 1:
The intrinsic base region is formed by selective epitaxial regrowth before final doping steps. This preliminary formation of the base structure with sharp interfaces allows subsequent doping to be performed at lower thermal budgets, achieving excellent dopant distribution without compromising downstream process throughput and enabling integration with CMOS processes.
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 results in high performance HBTs with lower resistance, reduced capacitance, and sharper dopant profiles, enhancing RF performance and device characteristics such as fT and fmax by improving the link resistance and dopant distribution.
Implementation Method 1
forming a recessed SiGe base with selective epitaxial regrowth
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to heterojunction bipolar transistors and methods of manufacture. The structure includes: a sub-collector region in a substrate; a collector region above the sub-collector region, the collector region composed of semiconductor material; an intrinsic base region composed of intrinsic base material surrounded by the semiconductor material above the collector region; and an emitter region above the intrinsic base region.