Source/Drain Contact Stack With Plasma Cleaning for Low Resistance
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Solution Overview
Problem
As semiconductor devices are scaled down, source/drain contact resistance becomes increasingly dominant in the conducting path of a transistor, with studies showing it can account for 51% or more of the total resistance, necessitating improvements in reducing this resistance.
Innovation Solution
A novel plasma cleaning process is applied to remove chemical compounds containing oxygen, such as metal oxides, that are inadvertently introduced between the source/drain semiconductor material and the highly conductive bulk metal layer, thereby reducing contact resistance without damaging the silicide layers and conductive barrier layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication processes are used without plasma cleaning, then the manufacturing process is simpler and faster, but source/drain contact resistance becomes excessively high (51% or more of total resistance)
Solution Approach 1:
The plasma cleaning process is performed as a preliminary step before depositing the bulk metal contact layer. This preliminary action removes oxygen compounds and contaminants from the source/drain surface, ensuring a clean interface that minimizes contact resistance before the metal contact is formed.
Solution Approach 2:
The plasma cleaning process uses reactive plasma species (such as oxygen plasma) to oxidize and remove carbon-containing contaminants and organic residues from the source/drain surface. The plasma environment creates a clean, oxide-free surface that improves metal-semiconductor contact properties.
2Reliability
If plasma cleaning is applied to remove oxygen compounds, then source/drain contact resistance is reduced, but the process temperature must be maintained at least 300°C which increases manufacturing complexity
Solution Approach 1:
The plasma cleaning process is conducted at elevated temperatures (at least 300°C) to enhance the effectiveness of oxygen compound removal. The temperature parameter is optimized to maximize plasma reactivity and cleaning efficiency while maintaining source/drain material integrity and achieving low contact resistance.
3Reliability
If plasma cleaning is performed to eliminate chemical compounds containing oxygen, then contact resistance is reduced, but the process time increases
Solution Approach 1:
The plasma cleaning step is integrated into the fabrication sequence as a preliminary treatment before metal contact deposition. By performing this cleaning action beforehand, the need for subsequent contact resistance correction steps is eliminated, optimizing the overall process timeline despite the added cleaning duration.
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
The plasma cleaning process effectively reduces source/drain contact resistance by eliminating oxygen compounds, improving the conductivity of the semiconductor device, and allowing for thinner conductive barrier layers, thereby enhancing the overall performance of the semiconductor device.
Implementation Method 1
A novel plasma cleaning process is applied to remove chemical compounds containing oxygen, such as metal oxides, that are inadvertently introduced between the source/drain semiconductor material and the highly conductive bulk metal layer
Data Source
AI summary
A semiconductor device includes a substrate, two semiconductor fins protruding from the substrate, an epitaxial feature over the two semiconductor fins and connected to the two semiconductor fins, a silicide layer over the epitaxial feature, a barrier layer over the silicide layer, and a metal layer over the barrier layer. The barrier layer includes a metal nitride. Along a boundary between the barrier layer and the metal layer, an atomic ratio of oxygen to metal nitride is about 0.15 to about 1.0.