FinFET Channel Insulation via Substrate Doping
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Solution Overview
Problem
FinFET transistors on bulk substrates face issues with leakage currents due to unintentional doping particle implantation, which affects carrier mobility and concentration, leading to uncontrolled electrical conduction properties and faceting of fin sides, making them incompatible with bulk substrates and increasing manufacturing costs when using SOI substrates.
Innovation Solution
A process involving epitaxial growth of a thin semiconductor fin on a bulk substrate, where doping particles are implanted into the substrate before fin formation, ensuring the fin is free from substrate doping particles, and using the same mask for both implantation and defining fin dimensions to create a controlled electrical junction that insulates the channel from the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping particles are implanted into the substrate before fin formation, then electrical insulation between channel and substrate is achieved, but unintentional doping of the fin occurs reducing carrier mobility
Solution Approach 1:
The patent applies preliminary action by forming the electrical junction in the substrate before the fin is grown. The doping particles are implanted into the substrate to create a junction that will subsequently provide electrical insulation. This preliminary doping step establishes the insulation structure before the fin formation process begins.
Solution Approach 2:
The patent uses an intermediary approach by introducing a mask layer that serves as a physical barrier during the doping process. The mask is positioned to protect the fin region from unwanted doping particles while allowing doping in the substrate. This intermediary mask structure enables selective doping to achieve insulation without contaminating the fin channel.
2Reliability
If oblique implantation is used to create electrical junction, then insulation is achieved, but doping particles penetrate into the fin causing faceting and uncontrolled electrical properties
Solution Approach 1:
The patent performs the doping action preliminarily before fin growth, establishing the electrical junction in the substrate beforehand. By timing the doping operation to occur before the fin is formed, the process ensures that doping particles cannot penetrate into the fin structure to cause faceting, while still achieving the desired electrical insulation effect.
Solution Approach 2:
The patent segments the doping process into distinct spatial zones using a mask. The mask divides the substrate surface into doped regions (for insulation) and protected regions (where the fin will grow). This segmentation ensures that doping particles are confined to specific areas and cannot reach the fin structure, preventing faceting while maintaining insulation.
3Reliability
If SOI substrate is used to eliminate leakage currents, then electrical insulation is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces the expensive SOI substrate with a standard bulk substrate combined with a relatively simple electrical junction structure. Instead of using costly pre-fabricated SOI wafers, the invention creates the necessary insulation through a doping-based electrical junction formed during the manufacturing process, significantly reducing material costs.
Solution Approach 2:
The patent introduces an electrical junction as an intermediary structure to achieve electrical insulation between the channel and substrate. This intermediary doping structure provides the necessary insulation function that would otherwise require expensive SOI substrates, enabling cost-effective implementation of leakage current reduction.
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 eliminates unintended doping effects, reduces leakage currents, and ensures reproducible electrical properties independent of fin width, achieving effective electrical insulation similar to MOS technology while maintaining high production yields.
Implementation Method 1
realizing an implantation of doping particles through the mask opening into the exposed part of the active portion of the substrate
Implementation Method 2
forming, by epitaxial growth from the part of the active portion exposed in the mask opening, a thin portion (fin) of crystalline semiconductor material
Data Source
AI summary
A finFET field effect transistor is produced by the formation of an electrical junction between the thin fin portion of semiconductor material which forms the channel of the transistor and the circuit substrate. Doping particles are implanted in the substrate through a mask which is then subsequently used to form the thin fin portion of the channel. The channel of the finFET transistor is thus electrically insulated from the circuit substrate in the same manner as in MOS integrated circuits realized from bulk silicon substrates.