As-deposited ZrO Research Articles

Infrared and Raman Spectroscopic Studies of Optically Transparent Zirconia (ZrO<SUB>2</SUB>) Films Deposited by Plasma-Assisted Reactive Pulsed Laser Deposition

Plasma-assisted pulsed laser deposited zirconia (ZrO(2)) films were studied by Fourier transform infrared (FT-IR) and Raman spectroscopy for structural characterization and thermal stability in combination with optical characterization by spectroscopic ellipsometry and optical transmission measurements. Only the monoclinic ZrO(2) phase was positively identified from the infrared and Raman spectra of the as-deposited ZrO(2) films, which show excellent optical transparency from the ultraviolet to the near infrared as revealed by optical characterization. The as-deposited ZrO(2) films are free of any SiO(x) interfacial layer when deposited on silicon. The prepared ZrO(2) films exhibit good thermal stability in their structural, optical, and interfacial properties up to 900 °C. Upon annealing above 1100 °C, a silicon oxide interfacial layer forms due to the oxidation of the silicon substrate surface by the oxygen diffused from the oxide film to the silicon substrate at high temperatures.

Plasma-enhanced flexible metal–insulator–metal capacitor using high- k ZrO 2 film as gate dielectric with improved reliability

We demonstrate a new flexible metal–insulator–metal capacitor using 9.5-nm-thick ZrO 2 film on a plastic polyimide substrate based on a simple and low-cost sol–gel precursor spin-coating process. The surface morphology of the ZrO 2 film was investigated using scan electron microscope and atomic force microscope. The as-deposited ZrO 2 film under suitable treatment of oxygen (O 2) plasma and then subsequent annealing at 250 °C exhibits superior low leakage current density of 9.0 × 10 −9 A/cm 2 at applied voltage of 5 V and maximum capacitance density of 13.3 fF/μm 2 at 1 MHz. The as-deposited sol–gel film was completely oxidized when we employed O 2 plasma at relatively low temperature and power (30 W), hence enhancing the electrical performance of the capacitor. The shift (Zr 3d from 184.1 eV to 184.64 eV) in X-ray photoelectron spectroscopy of the binding energy of the electrons towards higher binding energy; clearly indicates that the O 2 plasma reaction was most effective process for the complete oxidation of the sol–gel precursor at relatively low processing temperature.

Structural, optical properties and band gap alignments of ZrO xN y thin films on Si (1 0 0) by radio frequency sputtering at different deposition temperatures

ZrO x N y thin films have been prepared by radio frequency magnetron sputtering at various substrate temperatures. The effect of substrate temperature on structural, optical properties and energy-band alignments of as-deposited ZrO x N y thin films are investigated. Atomic force microscopy results indicate the decreased root-mean-square (rms) values with substrate temperature. Fourier transform infrared spectroscopy spectra indicate that an interfacial layer has been formed between Si substrate and ZrO x N y thin films during deposition. X-ray photoelectron spectroscopy and spectroscopy ellipsometry (SE) results indicate the increased nitrogen incorporation in ZrO x N y thin films and therefore, the decreased optical band gap ( E g) values as a result of the increased valence-band maximum and lowered conduction-band minimum.

Interfacial layer growth of ZrO 2 films on silicon

In this work, the interfacial layer growth for both as-deposited and annealed ZrO 2 thin films on silicon is analyzed in detail by the high-resolution cross-sectional transmission electron microscope and spectroscopic ellipsometry. For as-deposited ZrO 2/SiO 2/Si, the thickness of a SiO 2-like layer at the silicon interface was found to depend on the oxygen partial pressure during deposition. At oxygen partial pressure ratio of above 50% the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO 2 film and silicon consumption at the interface. At oxygen partial pressure ratio in the range 7–50%, the visible growth of interfacial silicon oxide layer was not present. The interfacial layer for ZrO 2/Si with optimal partial pressure (15%) during annealing at 600 °C was found to be the two-layer structure composed of the ZrSi x O y overlayer and the SiO x downlayer. The formation of the interfacial layer is well accounted for diffusion mechanisms involving Si indiffusion and grain-boundary diffusion.

Influence of pre-deposition treatments on the interfacial and electrical characteristics of ZrO 2 gate dielectrics

ZrO 2 films are deposited on bare silicon, silicon with a pre-sputtered ultrathin Zr metal layer, and plasma oxynitrided Si surface by reactive sputtering and the growth of interface layer between ZrO 2 and Si is investigated. The ZrO 2/Si dielectric stacks, before and after annealing in oxygen ambient, are characterized by grazing incident angle X-ray diffraction, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, capacitance–voltage and current–voltage measurements. The results reveal that as-deposited ZrO 2 films contain nanocrystallites embedded in the amorphous matrix. ZrO 2 films deposited on an ultrathin Zr metal layer show a thinner interface layer but contain a greater amount of oxide traps. ZrO 2 films deposited on SiO x N y grown by NH 3 plasma oxynitridation are found to retard the growth of the interface layer effectively, and they also exhibit fewer oxide traps and lower leakage currents.

A biomimetic approach to the deposition of ZrO 2 films on self-assembled nanoscale templates

Zirconium oxide thin films were deposited on a phosphonate-terminated self-assembled monolayer (SAM) on a single crystal silicon substrate by a hydrolysis of zirconium sulfate solution in acid environment at 80 °C. The ZrO 2 films consist of tetragonal ZrO 2 crystallites with a size of 5–10 nm. Surface nucleation and attraction between the SAM surface and bulk precipitates in solution can explain the film formation. In both mechanisms, the surface functionality of the SAM plays a crucial role. This deposition approach was inspired by biomineralization through controlled deposition of inorganic solids on an ordered organic matrix. Microstructures and mechanical properties of the ZrO 2 thin films were studied using scanning electron microscope (SEM), cross-sectional transmission electron microscope (TEM) and nanoindentation. Microstructures were tailored at different stages of the film growth, as well as with processing parameters and substrate surface conditions. The nanoindentation modulus and hardness of the as-deposited ZrO 2 films were much lower than those of the bulk ZrO 2. The addition of extra pressure during this process, however, restores mechanical properties of ZrO 2 films.

Preparation and characterization of ZrO 2 thin film on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

Silane coupling reagent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared on single-crystal Si substrate to form two-dimensional self-assembled monolayer (SAM) and the terminal SH group in the film was in situ oxidized to SO 3H group to endow the film with good chemisorption ability. Thus, ZrO 2 thin film were deposited on the oxidized MPTS-SAM, by enhanced hydrolysis of zirconium sulfate (Zr(SO 4) 2·4H 2O) solution in the presence of HCl at 70 °C, making use of the chemisorption ability of the SO 3H group. The thickness of the films was determined with an ellipsometer, while the chemical feature, phase composition, thermal stability, and morphology of the films were analyzed by means of Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, and atomic force microscopy. As the results, the as-deposited ZrO 2 film was composed of nanocrystalline tetragonal ZrO 2 (t-ZrO 2) and an amorphous basic zirconium sulfate. The annealing of the films at 500 °C led to crystallization to t-ZrO 2, while further heating to 800 °C eliminated S in the film, and the ZrO 2 film consisted of nanocrystalline tetragonal ZrO 2 and monoclinic ZrO 2 in this case. The as-deposited ZrO 2 thin films were compact and crack-free, showing quadratically-looking features which were not observed previously, while the thickness of the ZrO 2 films decreased with increasing annealing temperature. Since the ZrO 2 film was well adhered to the MPTS-SAM, it might find promising application in the surface-modification of single-crystal Si and SiC in microelectromechanical systems (MEMS).

Physical and electrical degradation of ZrO 2 thin films with aluminum electrodes

Zirconium oxide thin films were deposited on p-type (1 0 0) silicon wafers by reactive d.c. magnetron sputtering. The as-deposited ZrO 2 films at the power of 300 W and at room temperature were amorphous and the ZrO 2 films became polycrystalline with both the monoclinic and tetragonal phases after post-annealing at 450 °C in N 2 ambient. The ZrO 2 films with Al electrode had the interfacial amorphous Al–O-containing layer, which was formed by their interaction, but the films with inactive electrodes such as Pt had no additional interfacial layer. The value of the capacitance equivalent thickness (CET) for ZrO 2 film with Al electrode was increased to about 12.4 Å compared with the film with Pt electrode due to the additional interfacial layer between Al and ZrO 2 film. The difference of flat band voltage (Δ V FB) between the films with two different electrodes was about 1.2 V because of their work function difference.

Atomic layer chemical vapor deposition of ZrO2-based dielectric films: Nanostructure and nanochemistry

A 4 nm layer of ZrOx (targeted x∼2) was deposited on an interfacial layer (IL) of native oxide (SiO, t∼1.2 nm) surface on 200 mm Si wafers by a manufacturable atomic layer chemical vapor deposition technique at 300 °C. Some as-deposited layers were subjected to a postdeposition, rapid thermal annealing at 700 °C for 5 min in flowing oxygen at atmospheric pressure. The experimental x-ray diffraction, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and high-resolution parallel electron energy loss spectroscopy results showed that a multiphase and heterogeneous structure evolved, which we call the Zr–O/IL/Si stack. The as-deposited Zr-O layer was amorphous ZrO2-rich Zr silicate containing about 15% by volume of embedded ZrO2 nanocrystals, which transformed to a glass nanoceramic (with over 90% by volume of predominantly tetragonal-ZrO2 (t-ZrO2) and monoclinic-ZrO2 (m−ZrO2) nanocrystals) upon annealing. The formation of disordered amorphous regions within some of the nanocrystals, as well as crystalline regions with defects, probably gave rise to lattice strains and deformations. The interfacial layer (IL) was partitioned into an upper SiO2-rich Zr silicate and the lower SiOx. The latter was substoichiometric and the average oxidation state increased from Si0.86+ in SiO0.43 (as-deposited) to Si1.32+ in SiO0.66 (annealed). This high oxygen deficiency in SiOx was indicative of the low mobility of oxidizing specie in the Zr–O layer. The stacks were characterized for their dielectric properties in the Pt/{Zr–O/IL}/Si metal oxide-semiconductor capacitor (MOSCAP) configuration. The measured equivalent oxide thickness (EOT) was not consistent with the calculated EOT using a bilayer model of ZrO2 and SiO2, and the capacitance in accumulation (and therefore, EOT and kZr−O) was frequency dispersive, trends well documented in literature. This behavior is qualitatively explained in terms of the multilayer nanostructure and nanochemistry that evolves.

X-ray diffraction and electrical characterization of photo-CVD zirconium oxide layers

Zirconium oxide thin films grown by photo-induced chemical vapor deposition incorporating excimer UV lamps at deposition temperatures between 50 and 350 °C have been explored. The as-deposited ZrO 2 films grown at 200 °C exhibited a good leakage property with a current density of ∼3.0×10 −5 A/cm 2 at an electric field of 1 MV/cm, which was further improved to ∼2.0×10 −6 A/cm 2 after an UV anneal in O 2 at 400 °C for 10 min. With the annealing step, very few positive fixed charges with a Q f value of ∼2.0×10 10 and ∼3.0×10 9 cm −2 for the 200 and 300 °C deposited films were present near the ZrO 2/Si interface while the 300 °C deposited films also exhibited a lower interface trap density of 6.6×10 9 cm −2 eV −1. The as-deposited photo-CVD ZrO 2 layers started to crystallise at a temperature of 250 °C, giving a refractive index value of ∼2.1 at the temperature just above 300 °C.

Characteristics of ZrO 2 Thin Films by Atomic Layer Deposition for Alternative Gate Dielectric Applications

We investigated material and electrical properties of ZrO 2 films deposited by atomic layer deposition (ALD) using Zr t-butoxide and water (H 2 O). As-deposited ZrO 2 films show 2.4nm of CET measured at 100kHz with frequency dispersion and high leakage current (3A/cm2) at 1V. These undesirable properties may results from metallic Zr and carbon contamination in the films. The post-deposition annealing was performed in an O 2 ambient at 500 to improve the capacitance and reduce the leakage current. ZrO 2 films deposited by ALD and annealed at 500C exhibit CET(Capacitance Equivalent Thickness) of 2nm without dispersion issues and leakage current less than 10 m 3 A/cm 2 at 1V.

Characteristics of ZrO 2 Thin Films by Atomic Layer Deposition for Alternative Gate Dielectric Applications

We investigated material and electrical properties of ZrO 2 films deposited by atomic layer deposition (ALD) using Zr t-butoxide and water (H 2 O). As-deposited ZrO 2 films show 2.4nm of CET measured at 100kHz with frequency dispersion and high leakage current (3A/cm2) at 1V. These undesirable properties may results from metallic Zr and carbon contamination in the films. The post-deposition annealing was performed in an O 2 ambient at 500 to improve the capacitance and reduce the leakage current. ZrO 2 films deposited by ALD and annealed at 500C exhibit CET(Capacitance Equivalent Thickness) of 2nm without dispersion issues and leakage current less than 10 m 3 A/cm 2 at 1V.

Ion beam mixing of the ZrO 2/Fe system

ZrO 2 layers stabilized with 9 mol% Y 2O 3 of 35–100 nm thickness were deposited by sputtering on 200 nm thick Fe layers on SiO 2/Si. Ion beam mixing induced by 300 keV Kr ions and 1.5 MeV Br ions bombardment was studied at temperatures ranging from 100 to 300 K. Samples were analyzed by means of RBS, GXRD, and SEM techniques. RBS analysis revealed important atomic transport across the ZrO 2/Fe interface. The amount of intermixed atoms increases with increasing ion dose. Ion beam mixing was also observed at low temperatures. Upon 300 keV Kr-ion bombardment the tetragonal structure of as-deposited ZrO 2(Y 2O 3) layers was transformed into the cubic one. High energy ion bombardment produces only transformations of the crystalline structure without any visible atomic transport and the formation of the rare FeO – wuestite phase. Kr blistering was observed for samples implanted with 300 keV Kr ions to fluences exceeding 1 × 10 16 at./cm 2 at 100 K and 5 × 10 16 at./cm 2 at RT.