Source/Drain Epitaxial Stack With Non-Crystalline Layer for Larger Contacts
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Solution Overview
Problem
The challenge in fin-based field effect transistors is the limited contact area between the source/drain contacts and the epitaxial layers, leading to high resistance due to the crystallographic orientation of fin surfaces, which results in a diamond-shaped epitaxial structure with limited surface area for contacts.
Innovation Solution
Introduce a polycrystalline or amorphous layer during the epitaxial growth to inhibit facet formation, promoting a bulk-like shape with an enlarged top surface for the source/drain epitaxial structures, which includes materials like B-doped SiGe for PFETs and As- or P-doped Si for NFETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If epitaxial layer growth is performed on fin surfaces with crystallographic orientation, then the epitaxial structure forms with diamond shape, but the top surface area for source/drain contacts is limited
Solution Approach 1:
The patent changes the crystallographic orientation parameter of the fin surface from conventional orientations to <110> orientation. This parameter change fundamentally alters the epitaxial growth morphology, preventing diamond shape formation and creating a planar top surface with enlarged contact area while maintaining manufacturing precision through controlled epitaxial growth processes
Solution Approach 2:
The patent introduces a non-crystalline layer (amorphous or polycrystalline material) within the source/drain epitaxial stack. This composite structure combines the crystalline epitaxial layers with the non-crystalline intermediate layer, where the non-crystalline material fills gaps and promotes planar growth, thereby increasing the top surface area for contacts while maintaining overall structural integrity
2Device complexity
If the interfacial area between source/drain contacts and epitaxial layers is small, then the epitaxial structure is simpler, but the source/drain contact resistance increases
Solution Approach 1:
By changing the fin surface orientation to <110> and modifying the epitaxial growth parameters, the patent achieves a planar top surface configuration that naturally provides larger contact area without significantly increasing structural complexity. This parameter change directly addresses the contact resistance issue while keeping the epitaxial structure relatively simple
Solution Approach 2:
The non-crystalline layer acts as an intermediary within the epitaxial stack, promoting planar growth and ensuring good interface quality between the source/drain contacts and the underlying crystalline epitaxial layers. This intermediate layer helps maintain low contact resistance while keeping the overall structure manageable in complexity
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
Increases the effective contact area between the source/drain contact and the epitaxial structure, reducing resistance and inducing additional stress to the channel region, thereby improving transistor performance.
Implementation Method 1
Epitaxial layer growth on a fin can be based on a crystallographic orientation of the fin's surfaces such that epitaxially-grown source/drain regions may result in a top surface with limited surface area for the source/drain contacts
Data Source
AI summary
The present disclosure is directed to source/drain (S/D) epitaxial structures with enlarged top surfaces. In some embodiments, the S/D epitaxial structures include a first crystalline epitaxial layer comprising facets; a non-crystalline epitaxial layer on the first crystalline layer; and a second crystalline epitaxial layer on the non-crystalline epitaxial layer, where the second crystalline epitaxial layer is substantially facet-free.