Rare-Earth Scandate/TiN Gate Stacks in SOI MOSFETs Fabricated With a Full Replacement Gate Process

Terbium scandate (TbScO3) and lanthanum scan date (LaScO
₃
) have been investigated as gate dielectrics for metal-oxide-semiconductor field-effect transistors on both silicon-on-insulator (SOI) and strained SOI (sSOI) substrates. X-ray photoelectron spectroscopy analysis revealed the presence of a silicate at the interface for TbScO
³
on Si, whereas a silicate/SiO
₂
-like interface was found for the LaScO
₃
on Si. A full replacement gate process was developed to fabricate high-κ/metal gate fully depleted transistors on SOI and sSOI. LaScO
₃
transistors with a gate length of 2 μm show excellent characteristics with steep subthreshold slopes of 72 mV/dec, high I
_on
/I
_off
ratios, and electron mobility of 180 cm
²
/V · s for SOI and 375 cm
²
/V · s for sSOI at low field, which is superior to corresponding TbScO
₃
de vices. All sSOI transistors showed 2 times higher electron mobility than SOI reference devices.