Faceted Raised Source Drain Stress Liner Coupling
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Solution Overview
Problem
The effectiveness of the nitride stress liner in Extremely Thin Silicon-On-Insulator (ETSOI) Field-Effect Transistors (FETs) with a raised-source and drain (RSD) design is diminished due to reduced proximity to the Si interface, affecting transistor performance.
Innovation Solution
A transistor design featuring a buried oxide layer, a silicon layer with a gate stack including a high-k oxide layer and a metal gate, a nitride liner adjacent to the gate stack, an oxide liner adjacent to the nitride liner, and faceted raised source/drain regions formed epitaxially with angled sides to enhance nitride liner proximity to the channel, thereby improving stress coupling and reducing series resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a raised-source and drain (RSD) design is used in ETSOI FETs, then series resistance is reduced, but the proximity of the nitride stress liner to the Si interface is reduced, diminishing stress coupling effectiveness
Solution Approach 1:
The patent introduces a faceted geometry with angled side portions that create a three-dimensional structure. This dimensional change allows the nitride stress liner to be positioned closer to the Si interface in the vertical dimension while maintaining the raised source/drain structure's low resistance path. The faceted sides at angles of 10-75 degrees enable the stress liner to contact the silicon channel more effectively, resolving the contradiction between stress coupling and resistance reduction.
2Reliability
If the nitride stress liner is positioned closer to the Si interface, then stress coupling is improved, but series resistance increases
Solution Approach 1:
The raised source/drain structure is segmented into multiple faceted portions with different orientations. The angled side portions (10-75 degrees) provide stress coupling pathways closer to the interface, while the top portion maintains low resistance contact. This segmentation allows different regions to fulfill different functions: stress delivery and current conduction, thereby resolving the contradiction between stress coupling effectiveness and series resistance.
3Ease of manufacture
If conventional RSD structures are used, then manufacturing is simpler, but gate-to-source/drain parasitic capacitance is higher
Solution Approach 1:
The patent employs faceted surfaces with angled sides that create curved transition paths between the source/drain regions and the channel. This curved geometry reduces the overlapping area between the gate and source/drain regions compared to conventional vertical RSD structures, thereby reducing parasitic capacitance. The faceted structure maintains manufacturability through standard epitaxial growth and etching processes while achieving the capacitance reduction benefit.
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 design enhances the coupling of nitride stress to the channel, increasing mobility and drive current while minimizing gate-to-source/drain parasitic capacitance, resulting in improved transistor performance with reduced series resistance and capacitance.
Implementation Method 1
A faceted raised source/drain region is epitaxially formed adjacent to the nitride liner, the oxide liner, and first nitride spacer
Data Source
AI summary
A transistor is provided that includes a buried oxide layer above a substrate. A silicon layer is above the buried oxide layer. A gate stack is on the silicon layer, the gate stack including a high-k oxide layer on the silicon layer and a metal gate on the high-k oxide layer. A nitride liner is adjacent to the gate stack. An oxide liner is adjacent to the nitride liner. A set of faceted raised source/drain regions having a part including a portion of the silicon layer. The set of faceted raised source/drain regions also include a first faceted side portion and a second faceted side portion.