Epitaxial Strain of FET Source/Drain Structures via Bottom Isolation
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Solution Overview
Problem
Conventional semiconductor device fabrication techniques face challenges in achieving bottom isolation of source/drain structures without using a bottom dielectric isolation layer, which prevents epitaxial growth and strain of these structures.
Innovation Solution
The method involves creating a substrate with a doped upper layer of the same crystal structure as the source/drain structures, allowing for epitaxial growth of p-doped source/drain structures directly from the substrate without a bottom dielectric isolation layer, and forming pn-type diodes to achieve electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bottom dielectric isolation layer is used to electrically isolate source/drain structures from the substrate, then electrical isolation is achieved, but epitaxial growth and strain of the source/drain structures are prevented
Solution Approach 1:
The substrate is segmented into two distinct layers: an intrinsic semiconductor substrate body and a doped upper layer. This segmentation allows the source/drain structures to epitaxially grow from the doped upper layer while the intrinsic substrate body provides electrical isolation through reverse-biased pn junctions, thus resolving the contradiction between achieving electrical isolation and enabling epitaxial growth
Solution Approach 2:
A doped upper layer is introduced as an intermediary between the intrinsic substrate and the source/drain structures. This intermediary layer serves dual purposes: it enables epitaxial growth of the source/drain structures from its doped region while the pn junction formed between the doped upper layer and intrinsic substrate provides the necessary electrical isolation
2Object-generated harmful factors
If a bottom dielectric isolation layer is used to prevent leakage current, then leakage current is reduced, but the source/drain structures cannot be grown epitaxially from the substrate
Solution Approach 1:
By segmenting the substrate into an intrinsic body and a doped upper layer, the solution enables epitaxial growth with proper crystal structure alignment from the doped layer while the intrinsic substrate body acts as a barrier that reduces leakage current through reverse-biased pn junctions
Solution Approach 2:
The doping concentration parameter is changed in the upper layer of the substrate to create a doped region that enables epitaxial growth. This parameter change allows the source/drain structures to be grown with proper crystal orientation while the doping creates pn junctions that reduce leakage current
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 the fabrication of epitaxially strained p-type source/drain structures that are electrically isolated from the substrate without the need for a bottom dielectric isolation layer, enhancing their conductivity and reducing leakage current.
Implementation Method 1
epitaxially growing a p-doped source/drain structure from the n-doped exposed portion of the substrate
Implementation Method 2
the p-doped source/drain structures and the upper layer of the substrate form pn-type diodes
Data Source
AI summary
A MOSFET includes a semiconductor substrate, which has a body and an upper layer. The upper layer is doped differently than the body. The body and the upper layer are of a same crystal structure and orientation. The MOSFET also includes a p-type FET on the upper layer of the substrate. The p-type FET includes p-doped source/drain structures that sandwich one or more channels and a p gate stack with a p-type work function metal. In one or more embodiments, the p-doped source/drain structures are of the same crystal structure and orientation as the upper layer of the substrate and directly contact the upper layer of the substrate. In one or more embodiments, the upper layer of the substrate is doped differently than the p-doped source/drain structures, such that the p-doped source/drain structures and the upper layer of the substrate form pn-type diodes.