Tungsten (mid-gap) metal gates for ultra-thin dielectrics

With the reduction in CMOS device size, there has been a need to try and replace the poly-silicon gate with either one metal (near silicon mid-gap, φm~4.5 eV) or two metals, one each for nMOS and for pMOS with work- functions, φm ~ 4 and 5 eV respectively. For the mid-gap option, we discovered that tungsten was an ideal candidate due to its work-function, but the halide chemistries that were presently used were destroying the gate dielectric. We (myself and to others at IBM) discovered and implemented and new chemistry based on W(CO)6 which allowed us to deposit quality tungsten films in extremely thin gate dielectrics – well below 20Ǻ now. This work has been patented (US patent No 5,789,312) and for the 1999 calendar year, this patent reached the top 5% money-earners for the company, for which we were monetarily compensated. This work is still on-going and has led to many other applications within IBM’s microelectronics fabrications technologies.

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