You-Seok Suh

Properties of Ru-Ta alloys as gate electrodes for NMOS and PMOS silicon devices

This paper describes the characteristics of binary metallic alloys of Ta and Ru for gate electrode applications. The work function of this alloy can be varied from 4.2 eV to 5.2 eV by controlling the composition thereby enabling its use in both NMOS and PMOS devices. Excellent thermal stability up to 1000/spl deg/C was observed in alloy compositions suitable for both NMOS and PMOS devices. It is believed that the Ru/sub 1/Ta/sub 1/ phase of the film and formation of Ru-Ta bonds improves the thermal stability of the gate-dielectric interface while maintaining appropriate work functions.

Robust ternary metal gate electrodes for dual gate CMOS devices

This report describes thermally stable dual metal gate electrodes for surface channel Si CMOS devices. We found that the ternary metal nitrides, i.e., Ti/sub 1-x/Al/sub x/N/sub y/ (TiAlN) and TaSi/sub x/N/sub y/ (TaSiN) films, are stable up to 1000/spl deg/C. Especially, the stoichiometric TiAlN (y/spl sim/1) exhibited highly robust p-type gate electrode (p-TiAlN) properties, demonstrating a work function (/spl Phi//sub m/) of /spl sim/5.1 eV and excellent gate oxide integrity against the thermal budget of conventional Si CMOS processing. The N-deficient TiAlN (y < 1) showed /spl Phi//sub m/ for n-type electrode (n-TiAlN) with limited thermal stability. The dual gate electrodes, p-TiAlN and TaSiN, exhibited negligible EOT (equivalent oxide thickness) variation on the high-k gate dielectrics (ZrO/sub 2/, HfO/sub 2/) up to 950/spl deg/C.

Electrical characteristics of TaSixNy/SiO2/Si structures by Fowler-Nordheim current analysis

In this letter, the Fowler–Nordheim tunneling in TaSixNy/SiO2/p-Si structures has been analyzed. The effective barrier height at the metal–oxide interface was extracted by Fowler–Nordheim current analysis. The barrier height was found to increase with increased annealing temperature. The barrier height was correlated with the extracted work function from capacitance–voltage analysis. This indicated that the work function of TaSixNy films changes under high temperature annealing from 4.2∼4.3 eV after 400 °C anneals to ∼4.8 eV after 900 °C anneals. We believe that the mechanism that causes the work function to increase is the formation of a Ta-disilicide layer at the interface between the electrode and the dielectric.

Compatibility of dual metal gate electrodes with high-k dielectrics for CMOS

Dual metal electrodes such as Ru, Ru-Ta alloy, TaN and TaSiN were investigated on low EOT single layer HfO/sub 2/ and stacked HfO/sub 2//SiO/sub 2/ gate dielectrics. It was found that the work function values of metal gates on HfO/sub 2/ and on SiO/sub 2/ are similar. Thermal anneal studies of selected metals on the above dielectrics were also performed to evaluate the change in EOT and V/sub FB/ values.

Tunable work function dual metal gate technology for bulk and non-bulk CMOS

This paper describes a metal gate process, which provides tunable work function values and ease of integration for dual metal gate process flow. Vertical stacks of Ru and Ta layers were subjected to high temperature anneals to promote intermixing which resulted in /spl phi//sub m/ tuning. It was found that Ru/Ta stacks provided up to 0.4 eV reduction in /spl phi//sub m/ compared to Ru. To increase this change, stacks of Ru/sub 50/Ta/sub 50//Ru were also evaluated and nearly a 0.8 eV change in /spl phi//sub m/ was observed between Ru/sub 50/Ta/sub 50//Ru and Ru/sub 50/Ta/sub 50/ electrodes.

Effect of the composition on the electrical properties of TaSi/sub x/N y metal gate electrodes

In this letter, the effect of silicon and nitrogen on the electrical properties of TaSi/sub x/N/sub y/ gate electrode were investigated. The TaSi/sub x/N/sub y/ films were deposited on SiO/sub 2/ using reactive cosputtering of Ta and Si target in Ar and N/sub 2/ ambient. The thermal stability of TaSi/sub x/N/sub y//SiO/sub 2//p-type Si stacks was evaluated by measuring the flatband voltage and equivalent oxide thickness at 400/spl deg/C and 900/spl deg/C in Ar. It was found that under high temperature anneals, Si-rich TaSi/sub x/N/sub y/ films increased and this was attributed to the formation of a reaction layer at the electrode-dielectric interface. Reducing the Si content alone did not prevent the formation of this reaction layer while removing Si completely by utilizing TaN resulted in work functions that were too high. The presence of both Si and N was deemed necessary and their content was critical in obtaining optimized TaSi/sub x/N/sub y/ gates that are suitable for NMOS devices.

Electrical Characteristics of HfO2 Dielectrics with Ru Metal Gate Electrodes

Hafnium dioxide, HfO 2 , thin films were prepared by radio frequency magnetron sputtering of thin hafnium layers, followed by an oxidation process. Ru was deposited on the HfO 2 as the gate electrode. An equivalent oxide thickness of 12.5 A was obtained in Ru/HfO 2 /n-Si metal oxide semiconductor (MOS) capacitor with a low leakage current density of 1.7 × 10 - 2 A/cm 2 at Vg - V F B = 1 V in accumulation. The work function of Ru gate extracted from capacitance-voltage analysis was 5.02 eV, suggesting Ru has the appropriate work function for p-MOSFETs. Using the conductance method, a high interface state density of 1.3 X 10 1 3 eV - 1 cm - 2 from the conduction band edge to the near midgap of Si was obtained in Ru/HfO 2 /n-Si MOS, compared to low interface density level of ∼ 10 1 1 eV - 1 cm - 2 in p + poly Si/SiO 2 /n-Si MOS. To evaluate the thermal stability, the samples were subjected to a rapid thermal anneal in an argon ambient up to 900°C. The electrical characteristics of Ru/HfO 2 /n-Si MOS capacitor are discussed in detail with post-metal annealing temperatures.

Characteristics of TaSixNy thin films as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices

Reactively sputtered TaSixNy films have been investigated as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices. The as-deposited TaSixNy films were amorphous over a wide range of compositions. After annealing at 1000 °C, Ta30Si33N37 film became crystalline, however Ta26Si28N52 film remained amorphous. The x-ray photoelectron spectroscopy shows a significant increase of Si–N bonding in the TaSixNy films with increasing N content. The presence of Si–N bonds is attributed to cause the amorphous nature of the high N containing TaSixNy films. The work functions of TaSixNy films were extracted by capacitance–voltage analysis. The work function values for TaSixNy films with varying N contents range from 4.26 to 4.35 eV after forming gas annealing at 400 °C for 30 min, suggesting that TaSixNy films have work functions appropriate for n-type metal-oxide-semiconductor devices. However, it was observed, after 1000 °C anneals, that the work function of TaSixNy films increased to ∼4.8 eV...

Thermal Stability of TaSi x N y Films Deposited by Reactive Sputtering on SiO2

The thermal stability of TaSi x N y /SiO 2 /p-type Si metal-insulator-semiconductor structure has been evaluated by measuring equivalent oxide thickness (EOT) from capacitance-voltage curves and gate leakage current as a function of annealing temperatures. TaSi x N y films were deposited using reactive sputtering from a TaSi 2 target, varying the nitrogen/argon flow ratio. A reaction between Ta 53 Si 47 and SiO 2 was observed after a 1000°C anneal, resulting in the increase of interfacial roughness and oxide thickness in the TaSi x N y /SiO 2 /p-Si structures. Cross-sectional transmission electron microscopy shows no indication of an interfacial reaction or crystallization in Ta 22 Si 29 N 49 on SiO 2 up to 1000°C as manifested by the negligible change in EOT and the stable leakage currents density (2.0 x 10 -6 A/cm 2 at V g = -1 V). The presence of Si-N bonds is attributed to cause the amorphous nature of the high N-containing TaSi x N y films. This may retard the formation of an interface layer and improve the chemical-thermal stability of the gate electrode/dielectric interface and oxygen diffusion barrier properties under high-temperature annealing.

Physical and electrical analysis of RuxYy alloys for gate electrode applications

This letter describes RuxYy as a potential candidate for dual metal complementary metal–oxide–semiconductor applications. The characterization of RuY alloys indicate that the effective work function can be controlled from 3.9to5.0eV as the yttrium composition in the RuxYy is decreased in film for both PMOS and NMOS application. From x-ray photoelectron spectroscopy analysis, it was found that the Ru3d peaks do not change as the Y composition is changed, indicating the Ru–Y bonding is very weak or undetectable in RuxYy film. However, it was also found that Y reacts with the underlying SiO2 to form yttrium silicate. In addition, in situ x-ray diffraction results did not detect the presence of Ru–Y compound in the RuxYy films. Capacitance–voltage (C–V) characterization indicated that the oxide thickness decreased as the Y composition increased. We extracted the effective barrier height of RuxYy at the metal–oxide interface via Fowler–Nordheim current analysis. The barrier height decreases as the Y compositio...