Self-Aligned Vertical PNP Transistor for SiGe CBiCMOS
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Solution Overview
Problem
Conventional BiCMOS gate circuits experience performance degradation at low power supply due to Vbe voltage loss and substrate bias effects, limiting their application in deep sub-micron regimes.
Innovation Solution
The development of a Self-Aligned Vertical PNP Transistor for High Performance SiGe CBiCMOS Process, which involves forming a VPNP transistor with a VPNP emitter, base, and collector, using a substrate with NVPN and NPN regions, buried N and P regions, and an epi layer with n-doping, along with specific masking and implantation steps to create isolation regions and doped wells, allowing for efficient collector current flow and reduced resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional BiCMOS gate circuit is used with CMOS buffer and NPN output driver, then the circuit can operate in standard conditions, but performance degrades at low power supply due to Vbe voltage loss and substrate bias effect
Solution Approach 1:
The patent introduces a PNP transistor to complement the conventional NPN-based BiCMOS circuit. By inverting the transistor type from NPN to PNP, the circuit achieves rail-to-rail output swing without Vbe voltage loss, as the PNP transistor's emitter can be connected to Vcc directly, eliminating the voltage loss issue inherent in NPN-based designs.
Solution Approach 2:
The patent creates a complementary BiCMOS circuit that integrates both NPN and PNP transistors, allowing the circuit to function effectively across a wider range of power supply conditions. The PNP transistor serves multiple functions: it acts as an output driver, enables rail-to-rail swing, and eliminates the substrate bias effect that plagues conventional designs.
2Reliability
If PNP transistors are added to form complementary BiCMOS, then voltage loss is eliminated and performance at low power supply improves, but fabrication process complexity increases
Solution Approach 1:
The patent merges the fabrication processes for NPN and PNP transistors into a unified flow. By sharing common process steps such as epitaxial growth, ion implantation, and thermal processing, the patent reduces the overall fabrication complexity despite introducing PNP devices. The self-aligned structure further simplifies the process by eliminating additional masking steps.
Solution Approach 2:
The patent employs self-aligned structures where the PNP transistor components are automatically positioned relative to each other through the fabrication process itself, without requiring additional alignment steps. This self-alignment mechanism reduces fabrication complexity by eliminating manual or photo-lithographic alignment procedures.
3Productivity
If vertical PNP transistor structure is implemented, then transistor efficiency and current flow are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent performs preliminary actions during the fabrication process by pre-forming the collector and base regions with precise depth and positioning control through epitaxial growth and ion implantation. These preliminary structures are then used as templates for subsequent processing steps, ensuring that the final vertical PNP transistor achieves high efficiency without requiring ultra-precise alignment in later stages.
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 enhances the performance of SiGe CBiCMOS by eliminating voltage loss and improving transistor efficiency, enabling effective operation in deep sub-micron regimes and integration with CMOS devices.
Implementation Method 1
forming a buried P+ region adjacent to and above the buried N well region
Implementation Method 2
forming an epi layer over the substrate and the buried N well and the VPNP buried N region; the epi layer has a n-doping
Data Source
AI summary
A structure and a process for a self-aligned vertical PNP transistor for high performance SiGe CBiCMOS process. Embodiments include SiGe CBiCMOS with high-performance SiGe NPN transistors and PNP transistors. As the PNP transistors and NPN transistors contained different types of impurity profile, they need separate lithography and doping step for each transistor. The process is easy to integrate with existing CMOS process to save manufacturing time and cost. As plug-in module, fully integration with SiGe BiCMOS processes. High doping Polysilicon Emitter can increase hole injection efficiency from emitter to base, reduce emitter resistor, and form very shallow EB junction. Self-aligned N+ base implant can reduce base resistor and parasitical EB capacitor. Very low collector resistor benefits from BP layer. PNP transistor can be Isolated from other CMOS and NPN devices by BNwell, Nwell and BN+ junction.