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New nMOS material enables high-k dielectrics integration |
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Mar 30, 2006 at 01:54 PM |
 One of the holy grails of semiconductor process engineers is getting closer to a potentially successful conclusion with the announcement from SEMATECH that they have identified a metal electrode material that can be used to build reliable nMOS transistors while integrating high-k dielectrics.
At last years IEDM conference, continued pessimism existed that high-k materials would ever be used due to the continuous integration challenges researchers faced with replacing the trusted SiO2 (silicon dioxide).
A key challenge has been the fact that metal electrode materials previously tried would have reverted to unusable mid-gap workfunctions after going through CMOS device processing. SEMATECH has been working on this problem for three years with support from a range of Universities in the US. SEMATECH has said that the newly identified material showed an effective workfunction close to ~4.0eV,
"We systematically screened more than 250 material systems on various dielectrics," said Byoung Hun Lee, manager of the Advanced Gate Stack Program in SEMATECH's Front End Processes (FEP) Division. "From this work, we developed an understanding of how metal electrode materials and high-k dielectrics react, and how the effective workfunction of metal electrodes can be controlled to yield an effective workfunction close to that of doped polysilicon gates."
SEMATECH believes that metal gate nMOSFETs can now be used without changes to current CMOS processes.
However, the research consortium did not state when metal gates would enter volume production or at what technology node adoption would happen. At the IEDM conference numerous papers discussed alternative conventional solutions to metal gates and high-k dielectrics that enabled a work-around through the 32nm node, even though performance improvements would not be a significant if metal gates were adopted.
Only a very few materials have been found that have the correct work function with poly-silicon processes. But what works for NMOS transistors does not work for PMOS transistors, which means that no single metal can be used. Two materials have to be found with the correct work function for each type of transistor, and these materials both need to be compatible with both silicon and with each other.
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