FinFET Sub-Fin Leakage Control via Selective Isolation
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Solution Overview
Problem
As finFETs scale, it becomes challenging to electrically isolate sub-fin regions, leading to increased parasitic current flow and leakage, which can cause power consumption issues and potentially lead to circuit failure, with existing doping methods being limited in their ability to effectively isolate fine and dense finFET structures.
Innovation Solution
The techniques involve forming fins from a substrate, recessing the STI to expose a portion of the fin, and converting this exposed portion to an electrically isolating material through doping or oxidation, using processes like monolayer doping or thermal oxidation, with a barrier layer to prevent unwanted doping or oxidation of the active channel region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If finFETs are scaled down to increase transistor density, then device integration is improved, but sub-fin leakage increases due to difficulty in electrical isolation
Solution Approach 1:
The fin structure is segmented into distinct regions: an active channel region at the top and a sub-fin region below. Shallow trench isolation (STI) is recessed to expose only the sub-fin portion, allowing selective doping or oxidation of this lower region while preserving the active channel. This segmentation enables independent treatment of the sub-fin region to reduce leakage without affecting transistor operation.
Solution Approach 2:
Different regions of the fin structure are given different properties: the active channel region maintains its semiconductor characteristics for current flow, while the exposed sub-fin region is converted to an insulating material through doping or oxidation. This local differentiation of material properties allows the sub-fin region to act as an isolation barrier while the active channel remains conductive.
2Ease of manufacture
If existing doping methods are used for sub-fin isolation, then process simplicity is maintained, but isolation effectiveness is insufficient for fine and dense finFET structures
Solution Approach 1:
The STI is recessed beforehand to expose the sub-fin region before performing doping or oxidation. This preliminary exposure ensures that only the sub-fin portion is treated, preventing contamination of the active channel region. The barrier layer is also deposited in advance to protect the active channel during the isolation process, ensuring selective modification of only the intended region.
Solution Approach 2:
A barrier layer is introduced as an intermediary protective element between the doping/oxidation process and the active channel region. This barrier layer prevents unwanted diffusion or oxidation of the active channel while allowing the sub-fin region to be properly isolated. After the isolation process, the barrier layer can be removed, having served its protective function.
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 provides scalable and controlled sub-fin isolation, reducing leakage current and maintaining low leakage even under high temperature/time thermal processing, applicable to various transistor configurations including finFETs, nanowire transistors, and CMOS devices, enabling continued transistor scaling and power/performance improvements.
Implementation Method 1
converting this exposed portion to an electrically isolating material through doping or oxidation
Implementation Method 2
converting this exposed portion to an electrically isolating material through doping or oxidation
Data Source
AI summary
Techniques are disclosed for controlling transistor sub-fin leakage. The techniques can be used for highly scaled finFETs, as well as other non-planar transistors. In some cases, the techniques include exposing a middle portion of a fin structure formed on a substrate and then converting the exposed portion to an electrically isolating material via a doping or oxidation process. For example, a monolayer doping (MLD) process may be used to deliver dopants to the exposed portion of the fin in a self-saturated monolayer scheme. In another example case, thermal oxidation may be used to convert the exposed portion to an insulator material. In some cases, a barrier layer (e.g., including carbon doping) may be located above the exposed portion of the fin to help prevent the doping or oxidation process from affecting the upper region of the fin, which is used for the transistor channel.