Fabrication of midgap metal gates compatible with very thin SiO_2 films using low pressure chemically vapor deposited tungsten films

摘要

For future ULSI devices with a channel length below 0.1 mum the dopant concentration fluctuations result in large threshold voltage spreads [1],necessitating the use of undoped channels and of a gate material with Fermi level at the middle of the Si bandgap,so that it can be used for both p- and n-channel MOSFETs [2].The use of W gates is very attractive,as W offers a work function at the Si midgap,good conductivity and compatibility with very thin gate oxide processing.Tungsten deposition by CVD using W(CO)_6 has been developed [3],avoiding the adhesion problems of sputter-deposited W films.In this work,MOS capacitors with W gates on thin oxides are fabricated by a process used in conjunction with copper metallization,compatible with CMOS technology,and their electrical properties are characterized.