March 30, 2006 – SEMATECH says it has identified metal electrode materials for use with nMOS transistors with high-k dielectric, a big step on the way toward fabricating working CMOS devices using metal gate and high-k dielectric stacks.
High-k dielectrics have received much attention as an alternative to SiO2 gate dielectrics to help curb gate leakage current and improve scalability. However, efforts to fabricate metal-oxide semiconductor field-effect transistors comparable to polysilicon gate MOSFETs haven’t panned out — in some cases metal electrode materials with workfunctions similar to those of n+ or p+- type doped polysilicon gates became unusable after going through CMOS device processing, due to factors such as composition, underlying dielectric and heat cycles.
SEMATECH said its achievement involves nMOSFETs with metal electrodes showing an effective workfunction close to ~4.0eV, although it did not identify the exact metal or process used. SEMATECH said it would provide key data and process details to its members, and release full technical details during the 2006 Symposium on VLSI Technology in June. The work caps a three-year project involving nearly 40 engineers at SEMATECH and collaborating universities and suppliers.
“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 frontend 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.”