my phd research: the big picture
DESCRIPTION
Overview of my PhD research, for those who are not engineers or scientists.TRANSCRIPT
• Doctoral research performed at the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign, in collaboration with chemistry students in Dr. Gregory S. Girolami’s research group
Amount of assumed background knowledge and information:
Assumed knowledge areas: Basic chemistry and physics
Doctoral Research Overview
Teresa S. Spicer, PhD, [email protected]://www.linkedin.com/in/teresaspicer
Outline
Why are new ways of making thin layers of materials important?
Key findings
What is chemical vapor deposition?
What needs figuring out?
Why are new ways of making thin layers of materials important?
Integrated circuits have created a vital industry and enabled the telecommunications revolution
Semiconductor industry plays an important role in globalization, and therefore also in shaping our collective future.
Global Semiconductors Market Value, $ billion, 2004-2013(e)
Source: Datamonitor
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Image from http://www.textually.org/
Miniaturization drives integrated circuit development and applications
Image from http://tunicca.wordpress.com/2009/07/21/moores-law-the-effect-on-productivity/
Integrated circuits are made layer by layer by depositing thin layers or films of materials
Every material needed for an integrated circuit needs to be deposited as a thin film.
http://www.rigalab.com/Images/cross_section.jpg
webmedia.national.com/ gallery/52/52_rgb.jpg
Materials and thin film processing are key to miniaturization
In order to continue making smaller chips, thin films of new materials are required.
2007: 30 new materials introduced into 45-nm node1
1 A Thorough Examination of the Electronic Chemicals and Materials Markets, Businesswire, August 15, 2007 Image from http://www.intel.com/pressroom/kits/45nm/photos.htm
❝The implementation of high-k and metal materials marks the biggest change in transistor technology
since the introduction of polysilicon gate MOS transistors in the late
1960s.❞Gordon Moore, Intel Co-Founder, regarding two of the 30
new materials introduced in 2007
What is chemical vapor deposition?
What is Chemical Vapor Deposition?
Substrate Thermometer
Chemical Vapor Deposition (CVD) is a way of growing thin layers of materials, also called films.
1 2Chemicalreaction
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A main starting molecule, called
precursor, arrives at the hot growth
surface, the substrate, inside a vacuum
chamber.
The precursor molecule may ‘meet’ another molecule it
needs to react, called a reactant.
The precursor and reactant react.
Sometimes the warm surface alone can cause this step by
making the precursor decompose.
New molecules are now attached to the
substrate, one of which is hopefully the material we wanted to
grow.
Whatever isn’t the film leaves the surface.
Here we are growing a film of purple balls rather than green.
Substrate
Precursor
Precursor Reactant Atom of filmVolatile product Atom of film
A substrate up close, outside the chamber.
What needs figuring out?
The two major constraints for circuits are temperature and obtaining uniform coatings
Deep features need coating, but this is difficult to do evenly
Si Dopants
Si Dopants
Δ
http://www.pressebox.de/pressemeldungen/infineon-technologies-ag/boxid-28544.html
If dopants do not stay where they were put, the chips cease
to function.
Dopants diffuse with heat
How do you deposit the films at low temperature and do it evenly?
Deep holes need uniform coatings, but this is often slow
Pinch-off.
Conformal coating.
Conformal coating, but slow growth.
The ideal: completely uniform (conformal), fast coating.
Conformality = (ttop/tbottom)·100%
The problem: the hole ‘clogs’ at the top - pinch-off.
The impractical compromise: grow slowly so that the hole doesn’t have time to pinch off.
An opportunity exists to find a process that is fast but retains the uniformity of the coating.
} ttop
} tbottom
If the incoming molecules do not stick where they land first, conformality is possible
If the incoming molecules don’t stick immediately, coatings are more likely to be uniform.
The deposited atoms quickly
cause pinch-off.
High sticking probability Low sticking probability
Precursor molecules react or stick nearly
instantly
Precursor molecules bounce off the walls into
the trench.
Nearly conformal coverage.
Traditional CVD has a high reaction probability
Traditional CVD (at high temperatures)
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Traditional CVD often leads to pinch-off.
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With the right starting molecule, temperatures can be kept low and improve the conformality
Si Dopants
Si Dopants
Dopants diffuse, ruining chip
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High temperatures
Low temperature
Incoming molecules react as soon as they reach the surface, causing pinch-off
Dopants stayIncoming molecules do not react immediately enabling conformality
Precursor design is key to novel CVD process development
Enhance CVD conformality:
Low sticking probability
Precursor molecules bounce off the walls into
the trench.
Nearly conformal coverage.
Appropriate precursor stability:
Stable during handling
Reactive at low T
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Competitive advantage: collaboration with the Girolami chemistry group
State of the art analysis techniques at the Center of Microanalysis of Materials
Girolami group: Innovative new chemistry
Abelson group: State of the art vacuum chamber for growth
Key finding
Precursor design is key to novel CVD process development
Choose ligands purposefully: Ruthenium project
Siteblocking by ligands
Choose clever co-reactant: Manganese nitride project
Lability enables low-T CVD
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