Tonya M. Klein

Electrostatic tuning of ferromagnetic resonance and magnetoelectric interactions in ferrite-piezoelectric heterostructures grown by chemical vapor deposition

Magnetoelectric interactions as a function of applied electric field have been studied in ferrite-ferroelectric heterostructures at microwave frequencies. The measurements are performed on 1.5–2.0 μm thick nickel ferrite (NiFe2O4) films grown heteroepitaxially on lead zinc niobate-lead titanate and lead magnesium niobate-lead titanate substrates using direct liquid injection chemical vapor deposition. Large shifts in the ferromagnetic resonance profile are observed in these heterostructures due to strong magnetoelectric coupling resulting from electrostatic field induced changes in the magnetic anisotropy field. Theoretical estimates of field shifts are in good agreement with the experimental data.

Comparison of hafnium silicate thin films on silicon (1 0 0) deposited using thermal and plasma enhanced metal organic chemical vapor deposition

Hafnium silicate thin films were deposited by metal organic chemical vapor deposition (MOCVD) on Si at 400 °C using hafnium (IV) t-butoxide. Films annealed in O2 were compared to as-deposited films using X-ray photoelectron spectroscopy and X-ray diffraction. Hafnium silicate films were deposited by both thermal and plasma enhanced MOCVD using 2% SiH4 in He as the Si precursor. An O2 plasma increased Si content to as much as ∼26 at.% Si. Both thermal and plasma deposited Hf silicates are amorphous as deposited, however, thermal films exhibit crystallinity after anneal. Surface roughness as measured by atomic force microscopy was found to be 1.1 and 5.1 nm for MOCVD hafnium silicate and plasma enhanced MOCVD hafnium silicate, respectively.

Hydrogenated silicon nitride thin films deposited between 50 and 250 °C using nitrogen/silane mixtures with helium dilution

Silicon nitride thin films, deposited by plasma enhanced chemical vapor deposition at temperatures between 250 and 50 °C from SiH4, N2 and He, were characterized using transmission infrared spectroscopy, ellipsometry, wet etch rate, and current-voltage analysis. At 250 °C using SiH4/N2/He flow ratios of 1/150/75, films with refractive index=1.80 and H concentrations <20%, distributed equally in Si-H and N-H units were obtained. The concentration of hydrogen and its distribution in N-H and Si-H bonds are sensitive to process temperature, suggesting that thermally driven N incorporation reactions are important during growth. Inert gas dilution allows films to be formed at <100 °C, with bonded hydrogen configurations similar to films deposited at higher temperatures. Current versus voltage traces of as-deposited films show charge trapping, which can be reduced by extended low temperature anneals. These results show that chemical composition can be controlled in low temperature silicon nitride deposition. Thi...

Effect of nitrogen containing plasmas on interface stability of hafnium oxide ultrathin films on Si(100)

Hafnium oxide dielectric thin films were deposited by metalorganic chemical vapor deposition with Hf (IV) t-butoxide and either an O2, N2, or N2O plasma in a 1:1 ratio with helium. Films approximately 5nm thick were analyzed using angle-resolved x-ray photoelectron spectroscopy (XPS) and variable angle ellipsometry before and after heat treatment in an ultrahigh vacuum up to 470°C. Interdiffusion and/or reaction of the film with the silicon substrate, as measured by an increase in thickness and an increase in Si-O type bonding at the interface was most apparent with O2 plasma deposited films and least observed with N2 plasma deposited films. Also, the Hf(4f) XPS peak shifts toward higher binding energy after anneals for the N2 and N2O plasma deposited films indicates further oxidation of the film. In contrast, oxygen plasma deposited films do not exhibit a Hf(4f) peak shift. These results provide evidence that high-κ film∕substrate stability may be controlled by applying appropriate plasma chemistry.

Microstructural and ferromagnetic resonance properties of epitaxial nickel ferrite films grown by chemical vapor deposition

Microstructural and ferromagnetic resonance properties of epitaxial nickel ferrite (NiFe2O4) films grown by direct liquid injection chemical vapor deposition are reported. While high-quality epitaxial growth of NiFe2O4 films on (100)-oriented MgAl2O4 substrate is confirmed by high resolution transmission electron microscopy, bright field (diffraction contrast) TEM studies reveal the presence of dislocations and also dark diffused contrast areas, which originate from antiphase domains. Angle and frequency-dependent ferromagnetic resonance (FMR) experiments are conducted to determine the magnetic anisotropy and the magnetic relaxation. A low out-of-plane FMR linewidth of ∼160 Oe has been observed at a frequency of 10 GHz.

In situ attenuated total reflectance Fourier transform infrared spectroscopy of hafnium (IV) tert butoxide adsorption onto hydrogen terminated Si (100) and Si (111)

Hafnium oxide ultra thin films on Si are being developed to replace thermally grown SiO2 gates in complementary metal-oxide semiconductor devices. In this work, a specially designed attenuated total reflectance (ATR) Fourier transform infrared spectroscopy reaction cell has been developed to observe adsorption of hafnium (IV) t-butoxide (HtB) onto a Si (100), Si (111), and Ge ATR crystal heated to temperatures between 60 and 250°C and under 0.4torr of vacuum allowing the observation of initial reaction pathways in real time. Spectra generated by density functional theory calculations of monodentate and bridging adsorbed precursors as well as a spectrum of an applied liquid drop of HtB precursor were used to identify the chemisorbed species. Two symmetric O–tBu umbrella modes from bridged Si–O–Hf(O–tBu)2–O–Si located at 1226 and 1016cm−1 present in the chemisorbed spectra show the precursor dissociates and is present as a bridging ligand on both Si(100) and Si(111). Surface concentration of the chemisorbed...

Comparing magnetotransport and surface magnetic properties of half-metallic CrO2 films grown by low pressure and atmospheric pressure chemical vapor deposition

CrO2 films prepared by low pressure chemical vapor deposition (LPCVD) using Cr(CO)6 precursor have been investigated and compared with epitaxial half metallic CrO2 films prepared at atmospheric pressure (APCVD) using CrO3 precursor for their magnetotransport and surface magnetic properties. LPCVD films showed higher resistivity than APCVD epitaxial (100) CrO2 films prepared on (100) TiO2 substrates. Magnetoresistance of LPCVD films is comparable to that of APCVD films. X-ray magnetic circular dichroism suggests a reduced surface magnetic moment for LPCVD films. This reduced magnetic moment is attributed to antiferromagnetic alignment of the uncompensated Cr spins in the Cr2O3 surface layer.

Effect of O2 flow ratio on the microstructure and stress of room temperature reactively sputtered RuOx thin films

RuOx thin films were deposited at room temperature by reactive radio frequency magnetron-sputtering using Ar∕O2 discharges of varying O2 flow ratio (fO2) over the range 10%–50% and were characterized using x-ray diffraction, x-ray reflectivity, x-ray photoelectron spectroscopy, resistivity, and stress-temperature measurements. With the increase of fO2, the film texture changed from (110) to (101). Films deposited with fO2>25% were determined stoichiometric. The residual stresses in as-deposited films were all compressive and increased with addition of O2, except for the film sputtered at fO2=20% which was in biaxial tension. The film deposited at fO2=30% had a low resistivity value of 68μΩcm and near zero stress ( 25% were determined stoichiometric. The residual stresses in as-deposited films were all compressive and increased with addition of O2, except for the film sputtered at fO2=20% which was in biaxial tension. The film deposited at fO2=30% had a low resistivity value of 68μΩcm and near zero stress (<50MPa tensile) after a thermal cycle in air up to 500 °C which is promising for use in microdevices.

Si(100) Nitridation by Remote Plasmas for Enhanced High-κ Gate Performance

Hafnium oxide is the leading high-κ candidate for next generation CMOS devices, however, the material has a propensity to react with the Si(100) substrate, to crystallize, and to have fixed and trapped charges leading to low transistor mobilities. To address the reaction with the substrate, a remote N 2 /He plasma was used as a reactant during MOCVD with Hf (IV) t-butoxide which incorporates 6 at.% nitrogen located mostly at the film-substrate interface resulting in reduced interdiffusion upon anneal [1]. A new process for pretreating the silicon wafer with a N 2 /He plasma was developed to improve nitrogen concentrations at the interface and reduce interdiffusion further. Films deposited with N 2 /He plasma and the pretreatment method was compared to O 2 /He plasma deposited films and N 2 /He plasma deposited films without the nitridation step. It is shown that a 16Å interface SiN x layer is sufficient to prevent reaction during a 1000ºC Ar/O 2 anneal at atmosphere and an intermediate annealing step is crucial for desired reduction in interdiffion. Thick films show some crystalline peaks by XRD which are suppressed using the N 2 process. Electrical measurements on thick films show the pretreatment process results in the lowest leakage current density and the highest dielectric constant of 21.5.

Comparison of Chemical Vapor Deposited Hafnium Dioxide and Silicon Doped Hafnium Dioxide using either O 2 , N 2 O, H 2 O, O 2 plasma, or N 2 O plasma, and Hf (IV) t-butoxide

Hafnium oxide (HfO 2 ) and silicon containing hafnium oxide (HfSi x O y ) thin films were deposited by thermal and plasma enhanced chemical vapor deposition (PECVD) using Hf (IV) t-butoxide and either O 2 , N 2 O, H 2 O, O 2 plasma or N 2 O plasma as an oxygen source. Silane, 2% in He, was added to the reactant gas mixture to incorporate Si. Deposition rate and composition dependence on substrate temperature was studied and the deposited films were annealed in air for 30 min at 1100°C to observe changes in crystallinity and composition. Silicon incorporation was higher for H 2 O deposited HfSi x O y films (5 at.%) than O 2 and N 2 O deposited films (2 at.%) and had a lower deposition rate. Arrhenius plots reveal a non-simplistic reaction scheme since higher temperatures result in lower deposition rates due to precursor desorption. XRD indicate that as-deposited films using H 2 O are amorphous while O 2 and N 2 O deposited films are microcrystalline with a monoclinic phase.