Dielectrics based on the element hafnium look likely to be viable in 45nm processes, according to Belgian research centre IMEC.
The properties of hafnium dielectrics and ‘fully silicided’ nickel gates – both candidates for next-generation processes – have proved difficult to tune by the conventional doping techniques used with CMOS.
However, IMEC has now demonstrated the potential of using a NiSi gate for NMOS, and Ni2Si gate for PMOS, on a HfSiON dielectric, by using the approach to create a ring oscillator. IMEC calls its technology FUSI, or ‘fully silicided’.
FUSI offers a route to overcoming the problems of integrating poly-silicon gates with high-k gate dielectrics, because it exists in several different phases, which can be used to modulate Vt. However, in order to control the effect of different phases, the ratio of silicon thickness to that of nickel needs to be closely controlled. This is what IMEC has managed to do.
Luc van den hove, v-p of silicon process and device technology at IMEC, said there are still outstanding issues to do with thermal stability, reliability and process control, but the FUSI scheme promises to enable integration of metal gates and high-k materials at 45nm.
IMEC also found that the high Vt of NMOS Fets made using nickel FUSI can be reduced to a level that enables devices with a Vt down to 0.2V, by doping with the element ytterbium.
For more information:
www.imec.be