Chang Seok Kang

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.

Bias-temperature instabilities of polysilicon gate HfO/sub 2/ MOSFETs

Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs.

The electrical and material characterization of hafnium oxynitride gate dielectrics with TaN-gate electrode

Electrical and material characteristics of hafnium oxynitride (HfON) gate dielectrics have been studied in comparison with HfO/sub 2/. HfON was prepared by a deposition of HfN followed by post-deposition-anneal (PDA). By secondary ion mass spectroscopy (SIMS), incorporated nitrogen in the HfON was found to pile up at the dielectric/Si interface layer. Based on the SIMS profile, the interfacial layer (IL) composition of the HfON films appeared to be like hafnium-silicon-oxynitride (HfSiON) while the IL of the HfO/sub 2/ films seemed to be hafnium-silicate (HfSiO). HfON showed an increase of 300/spl deg/C in crystallization temperature compared to HfO/sub 2/. Dielectric constants of bulk and interface layer of HfON were 21 and 14, respectively. The dielectric constant of interfacial layer in HfON (/spl sim/14) is larger than that of HfO/sub 2/ (/spl sim/7.8). HfON dielectrics exhibit /spl sim/10/spl times/ lower leakage current (J) than HfO/sub 2/ for the same EOTs before post-metal anneal (PMA), while /spl sim/40/spl times/ lower J after PMA. The improved electrical properties of HfON over HfO/sub 2/ can be explained by the thicker physical thickness of HfON for the same equivalent oxide thickness (EOT) due to its higher dielectric constant as well as a more stable interface layer. Capacitance hysteresis (/spl Delta/V) of HfON capacitor was found to be slightly larger than that of HfO/sub 2/. Without high temperature forming gas anneal, nMOSFET with HfON gate dielectric showed a peak mobility of 71 cm/sup 2//Vsec. By high temperature forming gas anneal at 600/spl deg/C, mobility improved up to 256 cm/sup 2//Vsec.

Deposition and Electrical Characterization of Very Thin SrTiO3 Films for Ultra Large Scale Integrated Dynamic Random Access Memory Application

SrTiO3 thin films are deposited on Pt/SiO2/Si substrates using RF magnetron sputtering in a temperature range from 200° C to 600° C. The film deposited at 600° C shows the best dielectric property and leakage current characteristics due to its good crystallinity and stoichiometric composition. Dielectric constant of the film deposited at 600° C decreases with decreasing thickness from 235 at 120 nm to 145 at 30 nm. Leakage current shows a constant value of about 30 nA/cm2 at 1.6 V in a thickness range from 50 nm to 120 nm but increases rapidly to 5 µ A/cm2 at 30 nm. The electrical properties of the films are explained by a model of the Pt/SrTiO3/Pt capacitor based on the band structure.

Characterization of resistivity and work function of sputtered-TaN film for gate electrode applications

Tantalum nitride (TaN) films were prepared by reactive sputtering in a gas Ar and N2 for gate electrode applications. Resistivity, crystallinity, and work function of the films were investigated as a function of nitrogen flow rate. As the nitrogen flow rate increased from 0 to 20 sccm, the resistivity of as-deposited TaN films increased from 132 to 1.4×105 μΩ cm. With a nitrogen flow rate of 8 and 10 sccm, the fcc TaN phase was obtained. The work function of the TaN films was investigated using TaN-gated nmetal–oxide–semiconductor capacitors with SiO2 gate dielectrics of various thicknesses. As the nitrogen flow rate increased from 4 to 12 sccm, the work function decreased from 4.1 to 3.4 eV for as-deposited films. After annealing at 950 °C for 1 min, the work function increased to 4.5–4.7 eV, with less dependency on the nitrogen flow rate.

Improvement of surface carrier mobility of HfO/sub 2/ MOSFETs by high-temperature forming gas annealing

The surface electron mobility of HfO/sub 2/ NMOSFETs with a polysilicon gate electrode was studied in terms of the effects of high-temperature forming gas (FG) annealing. The high-temperature FG annealing significantly improved the drive current or the surface electron mobility of the NMOSFETs. Improvements were also observed in the subthreshold swings and the C-V characteristics, indicating a reduction in interfacial state density (D/sub it/). The D/sub it/ reduction was quantitatively confirmed by charge pumping current measurements. The mobility enhancement was achieved without degrading the equivalent oxide thickness (EOT) or gate leakage current. Different surface preparations, such as NH/sub 3/ or NO annealing, were explored to examine their effects on the NMOSFET performance. Mobility enhancement due to high-temperature FG annealing was also observed on these samples. Whereas NH/sub 3/ surface nitridation was effective in scaling EOT, the NO-annealed sample exhibited the highest mobility. Similar improvements were also observed on HfO/sub 2/ PMOSFETs, in terms of subthreshold swings, drive current, and surface hole mobility.

Electrical characterization and material evaluation of zirconium oxynitride gate dielectric in TaN-gated NMOSFETs with high-temperature forming gas annealing

The electrical, material, and reliability characteristics of zirconium oxynitride (Zr-oxynitride) gate dielectrics were evaluated. The nitrogen (/spl sim/1.7%) in Zr-oxynitride was primarily located at the Zr-oxynitride/Si interface and helped to preserve the composition of the nitrogen-doped Zr-silicate interfacial layer (IL) during annealing as compared to the ZrO/sub 2/ IL - resulting in improved thermal stability of the Zr-oxynitride. In addition, the Zr-oxynitride demonstrated a higher crystallization temperature (/spl sim/600/spl deg/C) as compared to ZrO/sub 2/ (/spl sim/400/spl deg/C). Reliability characterization was performed after TaN-gated nMOSFET fabrication of Zr-oxynitride and ZrO/sub 2/ devices with equivalent oxide thickness (EOTs) of 10.3 /spl Aring/ and 13.8 /spl Aring/, respectively. Time-zero dielectric breakdown and time-dependent dielectric breakdown (TDDB) characteristics revealed higher dielectric strength and effective breakdown field for the Zr-oxynitride. High-temperature forming gas (HTFG) annealing on TaN/Zr-oxynitride nMOSFETs with an EOT of 11.6 /spl Aring/ demonstrated reduced D/sub it/, which resulted in reduced swing (69 mV/decade), reduced off-state leakage current, higher transconductance, and higher mobility. The peak mobility was increased by almost fourfold from 97 cm/sup 2//V/spl middot/s to 383 cm/sup 2//V/spl middot/s after 600/spl deg/C HTFG annealing.

Structural and electrical properties of HfO 2 with top nitrogen incorporated layer

A novel technique to control the nitrogen profile in HfO/sub 2/ gate dielectric was developed using a reactive sputtering method. The incorporation of nitrogen in the upper layer of HfO/sub 2/ was achieved by sputter depositing a thin Hf/sub x/N/sub y/ layer on HfO/sub 2/, followed by reoxidation. This technique resulted in an improved output characteristics compared to the control sample. Leakage current density was significantly reduced by two orders of magnitude. The thermal stability in terms of structural and electrical properties was also enhanced, indicating that the nitrogen-doped process is effective in preventing oxygen diffusion through HfO/sub 2/. Boron penetration immunity was also improved by nitrogen-incorporation. It is concluded that the nitrogen-incorporation process is a promising technique to obtain high-k dielectric with thin equivalent oxide thickness and good interfacial quality.

Evaluation of silicon surface nitridation effects on ultra-thin ZrO2 gate dielectrics

The effects of silicon surface nitridation on metal–oxide–semiconductor capacitors with zirconium oxide (ZrO2) gate dielectrics were investigated. Surface nitridation was introduced via ammonia (NH3) annealing prior to ZrO2 sputter-deposition, and tantalum nitride (TaN) was used for the gate electrode. It was found that capacitors with the nitridation had thinner equivalent oxide thickness (∼8.7 A), comparable leakage current, and slightly increased capacitance–voltage hysteresis as compared to samples without nitridation. Additionally, transmission electron microscopy pictures revealed that nitrided samples had a thicker interfacial layer (IL), which had a higher dielectric constant than that of the non-nitrided IL.

Preparation and characterization of iridium oxide thin films grown by DC reactive sputtering

Iridium oxide ( IrO2) thin films were successfully grown by a DC magnetron reactive sputtering method. It was found that the crystalline nature and morphology of IrO2 films were strongly dependent on the oxygen partial pressure, total pressure and growth temperature. The growth of IrO2 is well explained by the generic curve for the total pressure as a function of O2 content. The films showed good barrier performance between Pt and poly-Si up to 750° C. A 40-nm-thick Ba0.5Sr0.5TiO3 film was grown by RF magnetron sputtering on the Pt/IrO2/poly-Si electrode. The leakage current density and dielectric constant of a Pt/Ba0.5Sr0.5TiO3/Pt capacitor on the IrO2/poly-Si electrode were comparable to those of the capacitor on a SiO2/Si substrate. However, an additional ohmic layer was required to prevent the formation of a SiO2 layer between the IrO2 and poly-Si.