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My PhD research: the big picture


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Overview of my PhD research, for those who are not engineers or scientists.

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My PhD research: the big picture

  1. 1. Doctoral Research Overview Teresa S. Spicer, PhD, PMP • 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
  2. 2. Outline Why are new ways of making thin layers of materials important? What is chemical vapor deposition? What needs figuring out? Key findings
  3. 3. Why are new ways of making thin layers of materials important?
  4. 4. Integrated circuits have created a vital industry and enabled the telecommunications revolution Global Semiconductors Market Value, $ billion, 2004-2013(e) 350 9 J 8 Market value (USD billions) 300 7 250 J J J 6 J % Growth 200 5 J 150 4 J 3 100 J J 2 50 1 0 0 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Source: Datamonitor Image from Semiconductor industry plays an important role in globalization, and therefore also in shaping our collective future.
  5. 5. Miniaturization drives integrated circuit development and applications Image from
  6. 6. Integrated circuits are made layer by layer by depositing thin layers or films of materials gallery/52/52_rgb.jpg Every material needed for an integrated circuit needs to be deposited as a thin film.
  7. 7. Materials and thin film processing are key to miniaturization 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 ❝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 In order to continue making smaller chips, thin films of new materials are required.
  8. 8. What is chemical vapor deposition?
  9. 9. What is Chemical Vapor Deposition? Precursor 1 2 3 4 5 Precursor Reactant Chemical Volatile product Atom of film Atom of film reaction Substrate A main starting The precursor The precursor and New molecules are Whatever isn’t the film molecule, called molecule may ‘meet’ reactant react. now attached to the leaves the surface. precursor, arrives at another molecule it Sometimes the warm substrate, one of Here we are growing a the hot growth needs to react, called surface alone can which is hopefully the film of purple balls surface, the substrate, a reactant. cause this step by material we wanted to rather than green. inside a vacuum making the precursor grow. chamber. decompose. Substrate Thermometer A substrate up close, outside the chamber. Chemical Vapor Deposition (CVD) is a way of growing thin layers of materials, also called films.
  10. 10. What needs figuring out?
  11. 11. The two major constraints for circuits are temperature and obtaining uniform coatings Deep features need coating, Dopants diffuse with heat but this is difficult to do evenly Dopants Si Δ Si Dopants If dopants do not stay where they were put, the chips cease to function. How do you deposit the films at low temperature and do it evenly?
  12. 12. Deep holes need uniform coatings, but this is often slow } ttop The ideal: completely uniform (conformal), fast coating. Conformality = (ttop/tbottom)·100% } tbottom Conformal coating. The problem: the hole ‘clogs’ at the top - pinch-off. Pinch-off. The impractical compromise: grow slowly so that the hole doesn’t have time to pinch off. Conformal coating, but slow growth. An opportunity exists to find a process that is fast but retains the uniformity of the coating.
  13. 13. If the incoming molecules do not stick where they land first, conformality is possible High sticking probability Low sticking probability Precursor Nearly conformal Precursor The deposited atoms quickly molecules bounce coverage. molecules react cause pinch-off. off the walls into or stick nearly the trench. instantly If the incoming molecules don’t stick immediately, coatings are more likely to be uniform.
  14. 14. Traditional CVD has a high reaction probability Traditional CVD O (at high temperatures) C O Ru C C C C O O O C C O C C O Ru O Ru O Traditional CVD often leads to pinch-off.
  15. 15. With the right starting molecule, temperatures can be kept low and improve the conformality High temperatures C C C O Ru O O Si Dopants Dopants diffuse, ruining chip Incoming molecules react as soon as they reach the surface, causing pinch-off Low temperature Dopants Si Incoming molecules do not react Dopants stay immediately enabling conformality
  16. 16. Precursor design is key to novel CVD process development Enhance CVD conformality: Appropriate precursor stability: Low sticking probability Stable during handling L M L Reactive at low T Precursor Nearly conformal L molecules bounce coverage. off the walls into L M M the trench.
  17. 17. Competitive advantage: collaboration with the Girolami chemistry group Girolami group: Innovative new chemistry Abelson group: State of the art vacuum chamber for growth State of the art analysis techniques at the Center of Microanalysis of Materials
  18. 18. Key finding
  19. 19. Precursor design is key to novel CVD process development Choose ligands purposefully: Choose clever co-reactant: Ruthenium project Manganese nitride project Siteblocking by ligands Lability enables low-T CVD t-Bu t-Bu N Mn N + NH3 t-Bu t-Bu Ru C C C O O O 80 ºC and up t-Bu H t-Bu N Mn N + H N L L L t-Bu H t-Bu