Cezhou Zhao

Thermal stability of neodymium aluminates high-κ dielectric deposited by liquid injection MOCVD using single-source heterometallic alkoxide precursors

Thin films of neodymium aluminate (NdAlOx) have been deposited by liquid injection metalorganic chemical vapor deposition (MOCVD) using the bimetallic alkoxide precursor [NdAl(OPri)6(PriOH)]2. The effects of high-temperature postdeposition annealing on NdAlOx thin films are reported. The as-deposited thin films are amorphous in nature. X-ray diffraction (XRD) and medium energy ion scattering (MEIS) show, respectively, no crystallization or interdiffusion of metal ions into the substrate after annealing at 950°C. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the thin films exhibited good electrical integrity following annealing. The dielectric permittivity (κ) of the annealed NdAlOx was 12, and a density of interface states at flatband (Dit) of 4.01 × 1011 cm-2 eV-1 was measured. The deposited NdAlOx thin films are shown to be able to endure high-temperature stress and capable of maintaining excellent dielectric properties.

Extrinsic and Intrinsic Frequency Dispersion of High-k Materials in Capacitance-Voltage Measurements

In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled based on a dual frequency technique. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was also studied. The effect of surface roughness on frequency dispersion is also discussed. After taking extrinsic frequency dispersion into account, the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Dielectric relaxation mechanisms are also discussed.

Dielectric relaxation of lanthanum doped zirconium oxide

Lanthanum doped zirconium oxide (Lax–Zr1−xO2−δ) films, with La contents, up to x=0.35, were studied. Films were annealed at 900u2009°C to crystallize them into phases with higher κ-values. Increasing the La content suppressed the monoclinic phase and stabilized the tetragonal or cubic phase. The highest dielectric constant was obtained for a lightly doped film with a La content of x=0.09, for which a κ-value of 40 was obtained. This was accompanied by a significant dielectric relaxation, following a single Curie–von Schweidler power-law dependency with frequency, changing to a mixed Curie–von Schweidler and Kohlrausch–Williams–Watts relationships after annealing. The dielectric relaxation was most severe for lightly doped films, which had the highest κ-values. The dielectric relaxation appears to be related to the size of crystal grains formed during annealing, which was dependent on the doping level.

High-k materials and their response to gamma ray radiation

The radiation response of four different high-k materials has been investigated by irradiating them using a 979 MBq Cs137 γ-ray source and a dose absorption rate of 0.71rad(Si)∕s. Acceptorlike electron traps and donorlike traps were observed in HfO2 and ZrO2 metal-oxide-semiconductor capacitors originating from radiation-induced defects. A lower density of donor-like traps were created in LaAlO3 and NdAlO3 capacitors, but both electron and hole trapping play a role in shifting the flat band voltage. The radiation hardness of the LaAlO3 and NdAlO3 thin films is similar to thermal SiO2 but better than the HfO2 and ZrO2.

Advanced CMOS Gate Stack: Present Research Progress

The decreasing sizes in complementary metal oxide semiconductor (CMOS) transistor technology require the replacement of SiO2 with gate dielectrics that have a high dielectric constant (high-k). When the SiO2 gate thickness is reduced below 1.4u2009nm, electron tunneling effects and high leakage currents occur which present serious obstacles for device reliability. In recent years, various alternative gate dielectrics have been researched. Following the introduction of HfO2 into the 45u2009nm process by Intel in 2007, the screening and selection of high-k gate stacks, understanding their properties, and their integration into CMOS technology have been a very active research area. This paper reviews the progress and efforts made in the recent years for high-k dielectrics, which can be potentially integrated into 22u2009nm (and beyond) technology nodes. Our work includes deposition techniques, physical characterization methods at the atomic scale, and device reliability as the focus. For most of the materials discussed here, structural and physical properties, dielectric relaxation issues, and projections towards future applications are also discussed.

Dielectric Relaxation of La-Doped Zirconia Caused by Annealing Ambient

La-doped zirconia films, deposited by ALD at 300°C, were found to be amorphous with dielectric constants (k-values) up to 19. A tetragonal or cubic phase was induced by post-deposition annealing (PDA) at 900°C in both nitrogen and air. Higher k-values (~32) were measured following PDA in air, but not after PDA in nitrogen. However, a significant dielectric relaxation was observed in the air-annealed film, and this is attributed to the formation of nano-crystallites. The relaxation behavior was modeled using the Curie–von Schweidler (CS) and Havriliak–Negami (HN) relationships. The k-value of the as-deposited films clearly shows a mixed CS and HN dependence on frequency. The CS dependence vanished after annealing in air, while the HN dependence disappeared after annealing in nitrogen.

Frequency dispersion and dielectric relaxation of La2Hf2O7

Thin films of La2Hf2O7 have been deposited by liquid injection atomic layer deposition and post-deposition annealed at 900°C. The dielectric frequency dispersion was more serious for thinner films which is attributed to the effect of a lossy interfacial layer between the La2Hf2O7 dielectric and silicon substrate. The effect of the interfacial layer was modeled based on a dual-frequency measurement technique. The dielectric relaxation of the La2Hf2O7 thin films was modelled using both the Curie-von Schweidler and Havriliak-Negami relationships. Post deposition annealing in nitrogen at 900°C for 15min improved dielectric relaxation and reduced the dielectric loss.

Dielectric relaxation of lanthanide-based ternary oxides: physical and mathematical models

Cerium-doped hafnium oxides (CexHf1-xO2) and lanthanum-doped zirconium oxides (LaxZr1-xO2) were investigated. The highest dielectric constants, k, were obtained from lightly doped oxides with an La content of x = 0.09 and a Ce content of x = 0.1, for which k-values of 33-40 were obtained. The dielectric relaxation appears to be related to the size of crystal grains formed during annealing, which was dependent on the doping level. The physical and mathematical models were used to analyze the relationship between k-values and frequencies. The variations in the k-values up tomegahertz frequencies for both CexHf1-xO2 and LaxZr1-xO2 are simulated based on the Curie-von Schweidler (CS) or Havriliak-Negami (HN) relationships. Concerning the lightly doped CexHf1-xO2 and LaxZr1-xO2, the data extracted are best modeled by the HN law, while LaxZr1-xO2 with doping level from x = 0.22 to 0.63 are best modelled based on the CS law.

Hysteresis in Lanthanide Zirconium Oxides Observed Using a Pulse CV Technique and including the Effect of High Temperature Annealing

A powerful characterization technique, pulse capacitance-voltage (CV) technique, was used to investigate oxide traps before and after annealing for lanthanide zirconium oxide thin films deposited on n-type Si (111) substrates at 300 °C by liquid injection Atomic Layer Deposition (ALD). The results indicated that: (1) more traps were observed compared to the conventional capacitance-voltage characterization method in LaZrOx; (2) the time-dependent trapping/de-trapping was influenced by the edge time, width and peak-to-peak voltage of a gate voltage pulse. Post deposition annealing was performed at 700 °C, 800 °C and 900 °C in N2 ambient for 15 s to the samples with 200 ALD cycles. The effect of the high temperature annealing on oxide traps and leakage current were subsequently explored. It showed that more traps were generated after annealing with the trap density increasing from 1.41 × 1012 cm−2 for as-deposited sample to 4.55 × 1012 cm−2 for the 800 °C annealed one. In addition, the leakage current density increase from about 10−6 A/cm2 at Vg = +0.5 V for the as-deposited sample to 10−3 A/cm2 at Vg = +0.5 V for the 900 °C annealed one.

Permittivity enhancement and dielectric relaxation of doped hafnium and zirconium oxide

The frequency dispersion of La doped zirconia and cerium doped hafnia films is considered. Doping at concentration of approximately 10% stabilizes crystalline phases with higher-k values. The dielectric relaxation of La doped zirconia films is more severe than the cerium doped hafnia.