Carrier Confinement via Barrier Layer in High Mobility FinFET
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Solution Overview
Problem
Existing FinFET technologies face challenges in carrier confinement and dopant diffusion due to limitations in growing wide band-gap materials in high aspect ratio trenches, leading to defects and reduced mobility, and high doping causing dopant migration.
Innovation Solution
A thin wide band-gap material is placed below the channel as a barrier layer to confine carriers and prevent dopant diffusion, reducing the need for lattice matching and minimizing seam formation, while using aspect ratio trapping trenches to limit defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wide band-gap materials are grown in high aspect ratio trenches to confine carriers, then carrier confinement is improved, but defects form due to growth interactions with trench sidewalls and seam formation occurs
Solution Approach 1:
The trench fill structure is segmented into multiple functional layers: a first trench fill material providing mechanical support and lattice matching, and a second trench fill material (wide band-gap) providing carrier confinement. This segmentation allows each material to perform its optimal function without the drawbacks of using a single material throughout the entire trench.
Solution Approach 2:
Different regions of the trench receive different fill materials based on local requirements. The bottom portion near the channel receives wide band-gap material for carrier confinement, while upper portions may receive lattice-matched materials for structural support. This local differentiation resolves the contradiction by providing carrier confinement only where needed without filling the entire trench with problematic wide band-gap material.
2Reliability
If high doping is used to confine carriers, then carrier confinement is improved, but dopant diffusion into the channel occurs reducing mobility
Solution Approach 1:
A lightly-doped or undoped wide band-gap trench fill material serves as an intermediary barrier between the heavily-doped substrate and the channel. This intermediary layer provides carrier confinement through its wide band-gap property without introducing high dopant concentrations that would diffuse into the channel and reduce mobility.
3Manufacturing precision
If trench fill materials are chosen for lattice matching to avoid defects, then manufacturing precision is improved, but the selection of wide band-gap materials is limited reducing carrier confinement effectiveness
Solution Approach 1:
The trench fill is segmented into a first material layer optimized for lattice matching with the substrate (reducing defects) and a second material layer optimized for wide band-gap properties (improving carrier confinement). This segmentation allows independent optimization of each function without compromise.
Solution Approach 2:
The trench fill employs a composite structure combining different semiconductor materials with complementary properties. The first trench fill material provides lattice matching, while the second provides wide band-gap characteristics, creating a composite system that achieves both defect reduction and effective carrier confinement.
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 improves transistor electrostatics, preserves high mobility, and allows for a wider selection of trench fill materials, enhancing device efficiency and repeatability.
Implementation Method 1
Carrier confinement can be obtained using several methods. One such method includes using heterojunction energy band offsets between the channel and the subfin (the area directly below the fin such as in a trench)
Implementation Method 2
Another such method obtains carrier confinement using doping of the subfin materials
Implementation Method 3
The thinness of the barrier layer reduces the need for lattice matching between the channel and the barrier layer
Implementation Method 4
aspect ratio trapping trenches to limit defects
Data Source
AI summary
An embodiment includes a device comprising: a trench that includes a doped trench material having: (a)(i) a first bulk lattice constant and (a)(ii) at least one of a group III-V material and a group IV material; a fin structure, directly over the trench, including fin material having: (b) (ii) a second bulk lattice constant and (b)(ii) at least one of a group III-V material and a group IV material; a barrier layer, within the trench and directly contacting a bottom surface of the fin, including a barrier layer material having a third bulk lattice constant; wherein (a) the trench has an aspect ratio (depth to width) of at least 1.5:1, and (b) the barrier layer has a height not greater than a critical thickness for the barrier layer material. Other embodiments are described herein.