FET Fin Structure With Offset Gate and Source-Drain Prongs
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Solution Overview
Problem
The miniaturization of transistors is hindered by limitations in contacted poly pitch (CPP) scaling due to gate length, source/drain contact area, and gate spacer width, making it challenging to further reduce the distance between transistor gates.
Innovation Solution
A method for forming a field-effect transistor (FET) device with a novel design that involves forming a fin structure with alternating channel and non-channel layers, allowing for the lateral etching of source, drain, and gate cavities, and the creation of body portions with prongs that are offset vertically, reducing the need for a spacer between the source/drain and gate terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional FET design with spacer separation is used, then electrical separation between gate and source/drain is sufficient, but contacted poly pitch (CPP) cannot be further scaled
Solution Approach 1:
The patent transitions from a planar spacer-based separation to a three-dimensional offset configuration where the gate body portion is laterally offset from the source/drain body portions. This dimensional change eliminates the need for vertical spacers while maintaining electrical separation through the offset geometry, enabling further CPP scaling.
Solution Approach 2:
The patent removes the spacer component entirely from the device structure. By extracting the spacer and replacing it with an offset body portion configuration, the design achieves electrical separation without requiring the spacer, thereby reducing CPP.
2Length of moving object
If gate length is reduced for scaling, then transistor footprint decreases, but source/drain contact area becomes insufficient
Solution Approach 1:
The patent extends the source/drain body portions vertically with prongs that protrude into the cavities, creating a three-dimensional contact structure. This vertical extension compensates for the reduced horizontal contact area caused by smaller gate length, maintaining sufficient contact area for current flow.
Solution Approach 2:
The source/drain prongs are nested within the cavities formed in the fin structure, with the prongs protruding into the cavity space. This nesting configuration maximizes the contact area within the available vertical and horizontal space, ensuring adequate contact area despite reduced gate length.
3Reliability
If chemical doping is used for source/drain regions, then conductivity is improved, but sub-threshold swing deteriorates and short-channel effects increase
Solution Approach 1:
The patent changes the doping parameter from chemical doping to dynamic doping. By applying reverse bias to the gate, the device dynamically modulates the doping state of the channel, achieving the necessary conductivity control without the harmful effects of fixed chemical doping, thereby improving sub-threshold swing and reducing short-channel effects.
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 enables further CPP scaling by reducing the separation between source/drain and gate body portions, facilitating dynamic doping and reducing the need for chemical doping, which in turn improves sub-threshold swing and minimizes short-channel effects.
Implementation Method 1
etching each of the first and second fin parts laterally from the first side such that a set of source cavities extending through the first fin part is formed in the first non-channel layers, and such that a set of drain cavities extending through the second fin part is formed in the first non-channel layers
Data Source
Figure 1
Figure 2~3
Figure 4a~4b
AI summary
According to an aspect, there is provided a method for forming a FET device, the method comprising: forming a fin structure; while masking the fin structure from a second side of the fin structure opposite a first side of the fin structure: - etching each of first and second fin parts laterally from the first side such that a set of source cavities and a set of drain cavities is formed in first non-channel layers in the first fin part and the second fin part, and - subsequently, forming a source body and a drain body, each comprising a respective common body portion along the first side and a set of prongs protruding from the respective common body portion into the source and drain cavities, respectively, and abutting the channel layers; and while masking the fin structure from the first side: - etching the third fin part laterally from the second side such that a set of gate cavities extending through the third fin part is formed in second non-channel layers, and - subsequently, forming a gate body comprising a common gate body portion along the second side and a set of gate prongs protruding from the common gate body portion into the gate cavities.