FinFET Varactor Doping Structure for Higher RF Quality Factor
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Solution Overview
Problem
FinFET varactors in integrated circuits face limitations in quality factor (Q) due to inherent fin structure resistance, which hinders high-frequency applications and degrades performance in RF technologies.
Innovation Solution
The implementation of dual N-type well doping and differential fin engineering techniques, including secondary shallow N-type doping and fin height and angle modifications, to reduce resistance and enhance the quality factor of FinFET varactors, compatible with current high-k metal-gate FINFET processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional FinFET structure is used, then device density is improved, but quality factor deteriorates due to inherent fin structure resistance
Solution Approach 1:
The patent applies local quality by implementing selective N-type doping in specific regions of the fin structure. The secondary shallow N-type doping is applied only in the channel region below the gate, creating localized conductivity enhancement where it is most needed for quality factor improvement, while maintaining the original fin structure elsewhere for density benefits.
Solution Approach 2:
The patent changes the electrical parameters of the fin structure by introducing dual N-type doping with specific concentration ranges (1e18 to 1e19 atoms/cm³ for secondary doping). This parameter modification increases carrier concentration and reduces resistance in the channel region, thereby improving quality factor without altering the fundamental FinFET geometry that enables high density.
2Reliability
If fin height is reduced to lower resistance, then quality factor is improved, but capacitance tunability deteriorates
Solution Approach 1:
Instead of changing the geometric parameter of fin height, the patent changes the electrical parameter by introducing secondary shallow N-type doping. This maintains the original fin height that provides good capacitance tunability while reducing resistance through increased carrier concentration, thus improving quality factor without sacrificing adaptability.
Solution Approach 2:
The patent creates an asymmetric doping profile with the secondary shallow N-type doping concentrated in the channel region below the gate. This asymmetric distribution optimizes resistance reduction where it is most critical for quality factor, while preserving the fin structure's capacitive characteristics that enable tunability.
3Reliability
If secondary shallow N-type doping is applied, then resistance is reduced and quality factor is improved, but fabrication complexity increases
Solution Approach 1:
The secondary shallow N-type doping is performed as a preliminary action before gate formation. By preparing the doped fin structure in advance, the patent simplifies subsequent processing steps and enables better control over the final device characteristics, offsetting the added doping step with overall process efficiency.
Solution Approach 2:
The dual N-type doping structure serves multiple functions: it reduces resistance for improved quality factor, maintains fin structure integrity for high density, and provides a foundation for subsequent gate and contact formation. This multi-functionality justifies the additional fabrication step by delivering multiple benefits from a single process modification.
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
These methods significantly improve the quality factor of FinFET varactors, enabling higher performance in RF applications by reducing resistance and improving capacitance tunability, thus supporting high-frequency operations.
Implementation Method 1
forming a second shallow N-type doping below the gate and above the N-type well
Data Source
AI summary
An integrated circuit structure comprises one or more fins extending above a surface of a substrate over an N-type well. A gate is over and in contact with the one or more fins. A second shallow N-type doping is below the gate and above the N-type well.