Electrical and physical characteristics of ultrathin hafnium silicate films with polycrystalline silicon and TaN gates

Metal-oxide-semiconductor transistors of ultrathin hafnium silicate films (equivalent oxide thickness (EOT) of 12.5–14 Å) with polycrystalline silicon and metal (TaN) gates have been demonstrated. Well-behaved transistor characteristics and EOT stability of Hf silicate with $n^{+}$ polysilicon indicates good compatibility with polysilicon gate process without use of barrier layer. Transmission electron microscopy analysis indicates that the films have no top interfacial layer with both TaN and polysilicon gates. The films also remain amorphous and show no indication of phase separation even after a 950 °C dopant activation anneal. Hf silicate films also show excellent transistor characteristics with TaN gate. ${\mathrm{NH}}_3$ pretreatment results in degraded transistor characteristics for TaN and poly gate samples. Good capacitance–voltage characteristics and negligible hysteresis (<10 mV) was observed in the capacitors after a 1000 °C activation indicating good electrical stability at high temperatures and minimal charge trapping.