Renee Nieh

Thermal stability and electrical characteristics of ultrathin hafnium oxide gate dielectric reoxidized with rapid thermal annealing

Dielectric properties of ultrathin hafnium oxide reoxidized with rapid thermal annealing (RTA) have been investigated. Capacitance equivalent oxide thickness (CET) of 45 A hafnium oxide was scaled down to ∼10 A with a leakage current less than 3×10−2 A/cm2 at −1.5 V (i.e., ∼2 V below VFB). Leakage current increase due to crystallization was not observed even after 900 °C rapid thermal annealing (RTA), but CET did increase after high temperature RTA due to the interfacial layer growth and possible silicate formation in the HfO2 film.

Electrical characteristics of highly reliable ultrathin hafnium oxide gate dielectric

Electrical and reliability properties of ultrathin HfO/sub 2/ have been investigated. Pt electroded MOS capacitors with HfO/sub 2/ gate dielectric (physical thickness /spl sim/45-135 /spl Aring/ and equivalent oxide thickness /spl sim/13.5-25 /spl Aring/) were fabricated. HfO/sub 2/ was deposited using reactive sputtering of a Hf target with O/sub 2/ modulation technique. The leakage current of the 45 /spl Aring/ HfO/sub 2/ sample was about 1/spl times/10/sup -4/ A/cm/sup 2/ at +1.0 V with a breakdown field /spl sim/8.5 MV/cm. Hysteresis was <100 mV after 500/spl deg/C annealing in N/sub 2/ ambient and there was no significant frequency dispersion of capacitance (<1%/dec.). It was also found that HfO/sub 2/ exhibits negligible charge trapping and excellent TDDB characteristics with more than ten years lifetime even at V/sub DD/=2.0 V.

Ultrathin hafnium oxide with low leakage and excellent reliability for alternative gate dielectric application

Physical, electrical and reliability characteristics of ultra thin HfO/sub 2/ as an alternative gate dielectric were studied for the first time. Crucial process parameters of oxygen modulated dc magnetron sputtering were optimized to achieve an equivalent oxide thickness (EOT) of 11.5 /spl Aring/ without deducting the quantum mechanical effect. Leakage current was 3/spl times/10/sup -2/ A/cm/sup 2/ at +1 V. Excellent dielectric properties such as high dielectric constant, low leakage current, good thermal stability, negligible dispersion and good reliability were demonstrated.

Bonding states and electrical properties of ultrathin HfOxNy gate dielectrics

Hafnium oxynitride (HfOxNy) gate dielectric was prepared using reactive sputtering followed by postdeposition annealing at 650 °C in a N2 ambient. Nitrogen incorporation in the dielectric was confirmed by x-ray photoelectron spectroscopy analysis. In comparison to HfO2 of the same physical thickness, HfOxNy gate dielectric showed lower equivalent oxide thickness (EOT) and lower leakage density (J). Even after a high-temperature postmetal anneal at 950 °C, an EOT of 9.6 A with J of 0.8 mA/cm2 @−1.5 V was obtained. In contrast, J of ∼20 mA/cm2 @−1.5 V for HfO2 with an EOT of 10 A was observed. The lower leakage current and superior thermal stability of HfOxNy can be attributed to the formation of silicon–nitrogen bonds at the gate dielectric/Si interface and strengthened immunity to oxygen diffusion by the incorporated nitrogen.

Electrical and reliability characteristics of ZrO2 deposited directly on Si for gate dielectric application

ZrO2 thin film has been studied as an alternative gate dielectric. It was deposited directly on a Si substrate by reactive sputtering. An equivalent oxide thickness of less than 11 A with a leakage current of 1.9×10−3 A/cm2 at −1.5 V relative to the flat band voltage has been obtained. Well-behaved capacitance–voltage characteristics with an interface state density of less than 1011 cm−2 eV−1 and no significant frequency dispersion have been achieved. Excellent reliability properties (e.g., low charge trapping rate, good time-dependent dielectric breakdown, low stress-induced leakage current, and high dielectric breakdown) have also been obtained.

MOSCAP and MOSFET characteristics using ZrO/sub 2/ gate dielectric deposited directly on Si

MOSCAP and MOSFET characteristics using ZrO/sub 2/ gate dielectric deposited directly on Si have been investigated. Thin equivalent oxide thickness (EOT), low leakage, negligible frequency dispersion, interface density less than 10/sup 11/ cm/sup -2/ eV/sup -1/, small hysteresis, excellent reliability characteristics have been demonstrated. The ZrO/sub 2/ film has been shown to be amorphous. A thin interfacial Zr-silicate layer (k>8) exists and is beneficial in maintaining good interfacial quality. This Zr-silicate layer grows after annealing and can be minimized through process optimization. Well-behaved p-channel MOS transistor characteristics with a subthreshold swing of 80 mV/decade have also been achieved.

Ultrathin zirconium silicate film with good thermal stability for alternative gate dielectric application

Zirconium silicate (ZrSixOy) films have been sputtered by comagnetron-reactive sputtering. The composition of ZrSixOy has been controlled by adjusting the sputtering powers of Si and Zr targets to achieve various effective dielectric constants. The sputtered silicate layers showed low equivalent oxide thickness of 14.5 A with a low leakage of 3.3×10−3 A/cm2 at −1.5 V relative to flat band voltage. The silicate films also exhibited good high-temperature stability and smooth interfacial properties on silicon substrate.

MOSFET devices with polysilicon on single-layer HfO/sub 2/ high-K dielectrics

MOSFETs and MOSCAPs of a single-layer thin HfO/sub 2/ gate dielectric with dual polysilicon gate were fabricated with self-aligned process and characterized. Polysilicon and dopant activation processes were optimized such that leakage current and equivalent oxide thickness (EOT) of HfO/sub 2/ remain low (EOT of 12.0 /spl Aring/. HfO/sub 2/ with 1/spl times/10/sup -3/ A/cm/sup 2/ at Vg=1.0 V). Reasonable N- and P-MOSFET characteristics such as subthreshold swing of 74 mV/decade and output currents were also demonstrated.

High-performance TaN/HfSiON/Si metal-oxide-semiconductor structures prepared by NH3 post-deposition anneal

Electrical and chemical characteristics of metal-oxide semiconductor field-effect transistors (MOSFETs) prepared by low-thermal-budget (∼600 °C) NH3 post-deposition annealing of HfSiON gate dielectric have been investigated. Compared to control Hf-silicate, HfSiON showed excellent thickness scalability, low leakage current density (J), and superior thermal stability. With proper annealing-time optimization, effective oxide thickness as low as 9.2 A with J<100 mA/cm2 at gate voltage Vg=−1.5 V has been achieved. C–V hysteresis of HfSiON MOSFET was found to be small (<20 mV). Unlike NH3 surface nitridation (NH3 pre-treatment prior to Hf-silicate deposition), no degradation in Gm (transconductance), Id–Vg (drain current–gate voltage), or Id–Vd (drain current–drain voltage) characteristics has been observed.

Performance of MOSFETs with ultra thin ZrO/sub 2/ and Zr silicate gate dielectrics

In this paper, we report the transistor performance of both PMOS and NMOS fabricated with ZrO/sub 2/ and Zr-silicate gate dielectrics. These high-k films exhibit low leakage, low subthreshold swing (S), and good on-off characteristics. Good effective electron and hole mobilities were obtained. It was found that for Zr-silicate, a mobility closer to thermal SiO/sub 2/ was demonstrated due to the better interface with Si substrate.