Electrical Properties of Ultrathin Hf-Ti-O Higher k Gate Dielectric Films and Their Application in ETSOI MOSFET

Abstract

Ultrathin Hf-Ti-O higher k gate dielectric films (~2.55 nm) have been prepared by atomic layer deposition. Their electrical properties and application in ETSOI (fully depleted extremely thin SOI) PMOSFETs were studied. It is found that at the Ti concentration of Ti/(Ti + Hf) ~9.4%, low equivalent gate oxide thickness (EOT) of ~0.69 nm and acceptable gate leakage current density of 0.61 A/cm² @ (V _fb - 1)V could be obtained. The conduction mechanism through the gate dielectric is dominated by the F-N tunneling in the gate voltage range of -0.5 to -2 V. Under the same physical thickness and process flow, lower EOT and higher I _on/I _off ratio could be obtained while using Hf-Ti-O as gate dielectric compared with HfO₂. With Hf-Ti-O as gate dielectric, two ETSOI PMOSFETs with gate width/gate length (W/L) of 0.5 μm/25 nm and 3 μm/40 nm show good performances such as high I _on, I _on/I _off ratio in the magnitude of 10⁵, and peak transconductance, as well as suitable threshold voltage (-0.3~-0.2 V). Particularly, ETSOI PMOSFETs show superior short-channel control capacity with DIBL <82 mV/V and subthreshold swing <70 mV/decade.

Keywords: Atomic layer deposition; ETSOI MOSFET; Electrical properties; Higher k; Ultrathin Hf-Ti-O gate dielectric films.

Fig. 1

(Color online) High-resolution cross-sectional TEM image of the Hf-Ti-O/IL/Si stack

Fig. 2

(Color online) XPS analysis of O 1s core level for Hf-Ti-O/IL/Si stack

Fig. 3

(Color online) Capacitance–voltage (C–V) curves at 1 MHz with a gate area of 100 × 100 μm² a with Hf-Ti-O as gate dielectric and b with HfO₂ as gate dielectric

Fig. 4

a Gate leakage current density versus gate voltage (J _g–V _g). b F-N tunneling mechanism

Fig. 5

(Color online) Typical transfer characteristics (I _d–V _g) of two ETSOI PMOSFETs with W/L = 3 μm/25 nm (—black square—V _ds = −0.05 V, V _ds = −0.9 V). a With HfO₂ as gate dielectric. b With Hf-Ti-O as gate dielectric

Fig. 6

(Color online) Typical transfer characteristics (I _d–V _g) of two ETSOI PMOSFETs with Hf-Ti-O as gate dielectric ((—black square—V _ds = −0.05 V, V _ds = −0.9 V). a W/L = 0.5 μm/25 nm. b W/L = 3 μm/40 nm

Fig. 7

Transconductance (g _m) versus gate voltage (V _g) curves of the two ETSOI PMOSFETs. a W/L = 0.5 μm/25 nm. b W/L = 3 μm/40 nm