Characteristics of high-k dielectric ECR-ALD lanthanum hafnium oxide (LHO) films

In this study, we investigated the characteristics of various lanthanum hafnium oxide (LHO) films with different lanthanum (La) concentrations deposited by an electron cyclotron resonance plasma-enhanced atomic layer deposition (ECR-ALD). Tris(isopropyl-cyclopentadienyl)lanthanum (La(iPrCp)₃) and tetrakis(ethylmethylamino)hafnium (TEMAHf) were utilized as the La and hafnium (Hf) precursors, respectively. When the La/(La + Hf) atomic percent ratio was 49.1%, the growth rate of the LHO film was 0.5 Å/cycle, with a dielectric constant of 16.3. As the La concentration was increased, the dielectric constant decreased. In addition, we found that a La-hydrate phase (La-O-H) can be easily formed when the La/(La + Hf) is over about 50%.     

Praseodymium compound formation in silicon by ion beam synthesis

The compound formation in the ternary system Pr-Si-O initiated by ion beam synthesis inside bulk-Si was studied by transmission electron microscopy and X-ray diffraction. The oxygen content was varied by additional O⁺ ion implantation and by oxidation of the bulk-Si. For annealing temperatures of 1100 °C, Pr silicate nanoclusters were observed consisting of Pr_9.33Si₆O₂₆ or Pr₂Si₂O₇. These silicates were the dominating and most stable Pr compounds. The interfaces between Pr silicate and the crystalline Si were atomically abrupt after high-temperature annealing. Pr silicide (PrSi₂) was detected for lower annealing temperatures such as 900 °C and for higher annealing temperatures in minor fraction also in samples with enhanced O content. Pr oxide (Pr₂O₃), the promising high-k material, was not definitely verified. In ion beam synthesis, the energy related to structural reordering during solid-state compound formation is a parameter that controls the proceeding processes in addition to other parameters like chemical reactivity and the compound interface matching.     

Synthesis, crystal structure and thermal decomposition of [La2(CH3CH2COO)6·(H2O)3]·3.5H2O precursor for high-k La2O3 thin films deposition

Lanthanum acetylacetonate La(C₅H₇O₂)₃·xH₂O has been used in the preparation of the precursor solution for the deposition of polycrystalline La₂O₃ thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La₂O₃ thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La₂O₃ phase.     

Preparation of CVD diamond coatings on gamma titanium aluminide using MPECVD with various interlayers

CVD diamond coatings were deposited on to γ-TiAl surfaces using a microwave plasma enhanced CVD to improve wear properties and the performance of γ-TiAl. Diamond coatings were directly deposited on to γ-TiAl substrates and deposited on to TiC, Ti₅Si₃, Al₂O₃ + TiO₂, and Si interlayers prepared on γ-TiAl substrates. The diamond coatings deposited directly on γ-TiAl suffered severe delamination and cracked. Those deposited on TiC and Ti₅Si₃ interlayers partially delaminated, whereas those deposited on Al₂O₃ + TiO₂ and Si interlayers adhered well to the underlying surfaces. The diamond films obtained were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectra showed that polycrystalline and nanocrystalline diamond films grew on γ-TiAl. Residual internal stresses of the diamond coatings deposited on interlayered-γ-TiAl were estimated experimentally from Raman spectra. The coatings prepared on Al₂O₃ + TiO₂/γ-TiAl and Si/γ-TiAl showed lower residual stresses.     

Effects of aluminum doping on lanthanum oxide gate dielectric films

This work reports a novel method for improving the electrical properties of lanthanum gate oxide (La₂O₃) by using aluminum doping and rapid thermal annealing (RTA) techniques. In the bulk of the Al-doped La₂O₃ film together with 600 °C RTA, we found that the aluminum atoms were incorporated into the oxide network and the film was transformed into lanthanum aluminate complex oxide. At the interface, a thin Al₂O₃ layer was formed. This interfacial Al₂O₃ layer suppressed the out-diffusion of substrate Si, the formation of interfacial silicate layer and silicide bonds. These effects resulted in a significant reduction on the bulk and interface trap densities and hence the gate leakage current.     

Influence of Ga2O3 addition on transparent conductive oxide films of In2O3-ZnO

Influence of incorporation of Ga in amorphous In-Zn-O transparent conductive oxide films was investigated as a function of Zn/(Zn + In). For In-Zn-O films with no Ga₂O₃, the range of Zn/(Zn + In) ratio where the amorphous phase appears became narrow at a substrate temperature of 250 °C. With increasing Ga₂O₃ quantity, amorphous films were obtained even at a high substrate temperature of 250 °C in a wider range of Zn/(Zn + In) than that of In-Zn-O films with no Ga₂O₃. This means that the trend of crystallization at higher substrate temperature was disturbed with additional Ga incorporation. For the film deposited from ZnO:Ga (Ga₂O₃: 4.5-7.5 wt%) and In₂O₃ targets, we obtained a resistivity of 2.8 × 10⁻⁴ Ω cm, nearly the same value as that for an In-Zn-O film with no Ga₂O₃. The addition of more than 7.5 wt% Ga₂O₃ induced a widening of the optical band gap.     

Deposition and post-deposition annealing of thin Y2O3 film on n-type Si in argon ambient

Thin (∼5.0 nm) Y₂O₃ films were deposited on n-type Si (1 0 0) substrate using RF magnetron sputtering. Detailed studies on the effects of post-deposition annealing (PDA) temperatures (400, 600, 800, and 1000 °C) in argon ambient on these films were performed by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), field emission scanning electron microscopy, and atomic force microscopy. Interfacial layer (IL) of SiO₂ in between Y₂O₃ and the Si substrate for sample annealed from 400 to 800 °C had been suggested from the results of FTIR. As for sample annealed at 1000 °C, presence of IL might consist of both Y₂Si₂O₇ and/or SiO₂ through the detection of Y₂Si₂O₇ compound and Si–O chemical bonding from XRD and FTIR analysis, respectively. For as-deposited sample, no detectable chemical functional group at the IL was recorded. Electrical characteristics of the Y₂O₃ films were acquired by fabricating metal-oxide–semiconductor capacitor as test structure. An improvement in the breakdown voltage (V_B) and leakage current density (J) was perceived as the PDA temperature increased. Of the PDA samples, the attainment of the lowest effective oxide charge, interface trap density, total interface trap density, and the highest barrier height at 1000 °C had contributed to the acquisition of the highest V_B and lowest J.     

On the use of photoacoustic technique for monitoring the thermal properties of lanthanum strontium cobalt ferrite-yttria stabilized zirconia two-layer systems

In this work, lanthanum strontium cobalt ferrite (La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ) films deposited by spray-pyrolysis onto commercial yttria stabilized zirconia substrates were investigated by photothermal spectroscopy. It is shown that by using the thermal-electrical analogy model it is possible to obtain the thermal properties of two-layer composite systems simultaneously, without the need to spread them, and thus to evaluate the thermal mismatch between the substrate and the deposited film. The thermal diffusivity of the 8YSZ substrate was found to be 6.6 × 10⁻³ cm²s⁻¹, whereas for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ films it ranged between 0.47 and 9.26 × 10⁻⁴ cm²s⁻¹. We have found that for film thickness beyond 3.06 μm the thermal expansion coefficient becomes relevant, indicating that the optimum film deposition time lies between 10 and 20 min.     

Thermal stability of amorphous molybdenum trioxide films prepared at different oxygen partial pressures by reactive DC magnetron sputtering

Thin films of MoO₃ were prepared on quartz and Si (1 0 0) substrates by reactive dc magnetron sputtering of a Mo target in an oxygen and argon atmosphere. The structural and optical changes induced in the films due to post-growth annealing have been systematically studied by Rutherford backscattering (RBS), X-ray diffraction (XRD), X-ray reflectivity (XRR) and by optical methods. RBS studies reveal no change in composition of the films upon annealing at high temperatures. Grazing angle XRD studies show that the as-deposited films are amorphous and crystallize to β-MoO₃ phase with small contribution of α-MoO₃ upon annealing at 300 °C. The film prepared at 0.40 Pa transforms to α-MoO₃ upon annealing at 650 °C, while the film deposited at 0.19 Pa still has some β-MoO₃ phase contribution. XRR measurements reveal that the film thickness decreases upon annealing with simultaneous increase of film density. The surface roughness of the films strongly increases after crystallization. The contraction of the film deposited at 0.40 Pa is much greater than the contraction of the film prepared at 0.19 Pa. The mass variation of the film deposited at 0.19 Pa and that deposited at 0.40 Pa are completely different. The optical properties of MoO₃ films deposited at 0.19 and 0.40 Pa are changed strongly by annealing.     

Crystallography of TiSi2 (C54) epitaxy on (111)Si and (001)Si surfaces

Following the success in understanding the textures in TiSi₂ (C49) epitaxy on (001)_Si surface using the edge-to-edge matching model that was originally developed for predicting the crystallographic features of diffusion-controlled phase transformations in solids, the present work applies this model to understand the in-plane texture in TiSi₂ (C54) thin films on Si single crystal surfaces and to explain why its epitaxial growth is more favoured on (111)_Si than on (001)_Si. Based on the actual atomic spacing along the matching directions across the interface between the thin films and the substrate, the model predicts most of the experimentally observed orientation relationships (ORs) and that the preferred order among the different systems is C49/(001)_Si system > C54/(111)_Si system > C49/(111)_Si system ≅ C54/(001)_Si system. The model has strong potential to be used to develop new thin film materials.     

La-substitution Bi2Ti2O7 thin films grown by chemical solution deposition

(La_0.05Bi_0.95)₂Ti₂O₇ (LBTO) thin films had been successfully prepared on P-type Si substrate by chemical solution deposition method. The structural properties of the films were studied by X-ray diffraction. The phase of (La_0.05Bi_0.95)₂Ti₂O₇ is more stable than the phase of Bi₂Ti₂O₇ without La substitution. The films exhibited good insulating properties with room temperature resistivities in the range of 10¹²-10¹³ Ω cm. The dielectric constant of the film annealed at 550 °C at 100 kHz was 157 and the dissipation factor was 0.076. The LBTO thin films can be used as storage capacitors in DRAM.     

Development of sputtered Shape Memory Alloy (SMA) Ni-Ti films for actuation in ice cooled environments

Due to the high sensitivity of Ni-Ti films to environmental changes, e.g. thermal, and/or to stress, they are ideal materials for applications on micro-sensors.It was aimed to obtain Ni-Ti films exhibiting the beginning of the B2 ⇔ R-phase transformation between room temperature (RT) and 0 °C. Thus, films with a slightly Ni-rich composition were prepared by sputtering, without intentional heating of the substrate. The Ni-Ti films were deposited on an Si₃N₄ intermediate layer previously deposited on naturally oxidized Si(100). The crystallization behaviour of the samples (at a constant temperature of 430 °C) was studied by X-ray diffraction in grazing incidence geometry off-plane (GIXD) at a synchrotron-radiation beamline. The GIXD patterns obtained during the annealing process of the Ni-Ti polycrystalline films revealed mainly an austenitic structure (B2 phase) and the precipitation of Ni₄Ti₃. The results have also shown that the presence of an intermediate layer of Si₃N₄ enhances the crystallization process of the Ni-Ti sputtered films when compared to the films deposited directly on single-crystal Si (with native oxide).The phase transformation behaviour of the Ni-Ti film on Si₃N₄ was evaluated by XRD in off-plane Bragg-Brentano geometry during cooling (RT → −40 °C) and heating (−40 °C → RT). It has been observed that a high fraction of the Ni-Ti film is already transformed to R-phase at 9 °C (austenitic at RT), as well as a very small temperature hysteresis for the B2 ⇔ R-phase transformation.After the characterization described above, the film was removed from the substrate. The free-standing film showed a pronounced “two-way” shape memory effect (SME). In the austenitic state the film presents a flat shape. During cooling, by reducing its distance from ice cubes (i.e., decreasing the surrounding temperature), the film starts bending exhibiting a final curled shape (yet without touching the ice). On heating it recovers its flat shape. The authors attribute the nature of this “two-way” SME to the Ni₄Ti₃ precipitates that formed during the heat treatment.     

Electronic properties of BaTiO3/4H-SiC interface

The possibility of barium titanate (BaTiO₃) application in silicon carbide (SiC) technology has been elaborated in terms of the dielectric film quality and properties of the BaTiO₃/4H-SiC interface. High resistivity, high-k thin films containing La₂O₃ admixture were applied as gate insulator of metal-insulator-semiconductor (MIS) structure. The thin films were deposited by means of radio frequency plasma sputtering (RF PS) of sintered BaTiO₃ + La₂O₃ (2 wt.%) target on 8° off-axis 4H-SiC (0001) epitaxial layers doped with nitrogen. The results of current-voltage and capacitance-voltage measurements are presented for MIS capacitors.     

Growth,chemical composition,and structure of thin La x Hf1 − x O y films on Si

The chemical structure, phase composition, and crystal structure of La _x Hf_{1 ? x} O _y films grown on Si using volatile metalorganic compounds as Hf and La precursors have been studied by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray microanalysis, and atomic force microscopy. By varying the lanthanum and hafnium source temperatures, we were able to grow films with 2 at % < C_La < 30 at %. The Hf 4f and La 3d peak positions in the XPS spectra of the films correspond to hafnium and lanthanum in the Hf⁴⁺ and La³⁺ states. With increasing La concentration, the reflections in the X-ray diffraction patterns of the films shift to smaller 2θ angles, indicating the formation of solid solutions. At 18 at % La, we observed a transition from a fluorite-like structure to the pyrochlore structure (La₂Hf₂O₇). The film containing 30 at % La consisted of a mixture of c-La₂O₃ and La₂Hf₂O₇. The surface roughness of the films was shown to increase with increasing La concentration. Capacitance-voltage (C-V) measurements were used to assess the relative permittivity (k) of the films as a function of La concentration. The minimum k value was obtained at the La concentration corresponding to the transition from the fluorite structure to an ordered pyrochlore structure (second-order phase transition).     

High-temperature stability of the mechanical and optical properties of Si–B–C–N films prepared by magnetron sputtering

Quaternary Si–B–C–N materials are becoming increasingly attractive due to their possible high-temperature and harsh-environment applications. In this work, amorphous Si–B–C–N films with two compositions (Si₃₄B₉C₄N₄₉ and Si₃₆B₁₃C₇N₄₀) and low contamination level (H + O + Ar < 4 at.%) were deposited on silicon substrates by reactive dc magnetron co-sputtering using two different targets and gas mixtures. Thermal stability of these films was investigated in terms of composition, bonding structure, as well as mechanical and optical properties after annealing in helium up to a 1300°C substrate limit. Films with a high nitrogen content (Si₃₄B₉C₄N₄₉, i.e. N/[Si + B + C]~ 1.0) were found to be stable up to 1300°C. After annealing, the hardness and elastic recovery of those films slightly increased up to 27 GPa and 84%, respectively, and the reduced Young's modulus remained practically constant (~ 170 GPa). The refractive index and the extinction coefficient at 550 nm were evaluated at 2.0 and 5 × 10^− 4, respectively, and the optical band gap was approximately 3.0 eV. In contrast, films with a lower nitrogen content (Si₃₆B₁₃C₇N₄₀, i.e. N/[Si + B + C]~ 0.7) were stable only up to 1200°C. Both Si–B–C–N materials studied here exhibited extremely high oxidation resistance in air up to the 1300°C substrate limit.     

Evolution of silicon nanoclusters and hydrogen in SiNx:H films: Influence of high hydrostatic pressure under annealing

Hydrogenated silicon-rich nitride (SRN) films of various stoichiometry (SiN_x:H, 0.7 < x ≤ 1.3) were deposited on single-crystalline Si substrates with the use of plasma enhanced chemical vapor deposition at a temperature of 100 °С. Furnace annealing for 5 h in ambient Ar at 1130 °С under atmospheric and enhanced hydrostatic pressure (HP — 11 kbar, 1.1 GPa) was applied to modify the structure of the films. The properties of as-deposited and annealed films were studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence (PL), as well as high-resolution transmittance electron microscopy (HRTEM). According to the Raman data, the as-deposited film, in which the stoichiometry parameter x is below 1.0, contains amorphous silicon nanoclusters. Furnace annealing leads to crystallization of the nanoclusters. From the HRTEM and Raman data, the average size of the Si nanocrystals in the annealed films was 6-7 nm. No silicon nanoclusters were observed in the as-deposited films with relatively low concentration of excessive silicon atoms (the case of SiN_x:H, x > 1); furnace annealing leads to segregation of the Si and Si₃N₄ phases, so, the amorphous Si clusters were observed in annealed films according to Raman data. Surprisingly, after annealing with such high thermal budget, according to the FTIR data, the SRN film with parameter x close to that of the stoichiometric silicon nitride contains hydrogen in the form of SiH bonds. From analysis of the FTIR data of the SiN bond vibrations one can conclude that silicon nitride is partly crystallized in the films with x > 1 after annealing for 5 h. No influence of HP on the structure of Si nanoclusters was observed in the case of SRN films with x ≤ 1.1. Dramatic changes in the PL spectra of the SRN films with the x parameter close to that of the stoichiometric silicon nitride (x ≈ 1.3), annealed under atmospheric pressure and HP, were observed. HP stimulates the formation of very small hydrogenated amorphous nanoclusters. The size of amorphous Si nanoclusters determined from the quantum size effect model describing the PL spectra, should be 2-4 nm in this case.     

Effect of high temperature post-annealing of La0.7Sr0.3MnO3 films deposited by radio frequency magnetron sputtering on SiO2/Si substrates heated at low temperature

La_0.7Sr_0.3MnO₃ thin films were deposited on SiO₂/Si substrates by RF magnetron sputtering under different oxygen gas flow rates with a sputtering power of 100 W. During deposition, the substrate was heated at 623 K. To investigate post-annealing effects, the as-deposited La_0.7Sr_0.3MnO₃ thin films were thermal-treated at 973 K for 1 h. The effects of oxygen gas flow rate and post-annealing treatment on the physical properties of the films were systematically studied. X-ray diffraction results show that the growth orientation and crystallinity of the films were greatly affected by the oxygen gas flow rate and substrate heating during deposition. The sheet resistance of the films gradually decreased with increasing oxygen gas flow rate, while the post-annealed films showed the opposite behavior. The temperature coefficient of resistance at 300 K of La_0.7Sr_0.3MnO₃ thin films deposited at an oxygen gas flow rate of 40 sccm decreased from − 2.40%/K to − 1.73%/K after post annealing. The crystalline state of the La_0.7Sr_0.3MnO₃ thin films also affected its electrical properties.     

Enhanced characterization of ITO films deposited on PET by RF superimposed DC magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited on polyethylene terephthalate substrates by RF superimposed DC magnetron sputtering using an ITO target composed of In₂O₃ (90 wt.%):SnO₂ (10 wt.%). The total sputtering power was maintained at 70 W and the power ratio of RF/(RF + DC) was varied from 0 to 100% in steps of 25%. The discharge voltage and deposition rate decreased with increasing RF/(RF + DC) power ratio. The ITO film deposited at a 50% RF portion of the total power showed the lowest resistivity (3.18 × 10^− 4 Ωcm), high transmittance (87.5%) and relatively good mechanical durability, which was evaluated using bending and scratch tests.     

Resistive switching behavior of (Zn1−xMgx)O films prepared by sol-gel processes

Highly c-axis oriented sol-gel (Zn_1 − xMg_x)O films were deposited on Pt/Ti/SiO2/Si substrates. Resistive switching behaviors with stable switching and high resistance ratio were demonstrated for the Pt/(Zn_0.9Mg_0.1)O/Pt stacks. The effect of the film thickness and the annealing temperature on resistive switching was discussed. Higher substitution of Mg for Zn results in higher resistance of (Zn_1 − xMg_x)O films, which is beneficial for resistive switching to occur at thinner film thickness. The mechanisms dominating the low and the high resistance states are Ohmic conduction and Poole-Frenkel emission, respectively. The resistance ratio varies from 140 to 1000, which is much higher than the value 25 reported recently for sol-gel (Zn_0.8Mg_0.2)O films. Films annealed at higher annealing temperatures possess higher resistance ratio.     

Atomic layer deposition of ferromagnetic cobalt doped titanium oxide thin films

TiO₂ thin films doped or mixed with cobalt oxide were grown by atomic layer deposition using titanium tetramethoxide and cobalt(III)acetylacetonate as metal precursors. The films could be deposited using both O₃ and H₂O as oxygen precursors. The films grown using water exhibited considerably smoother surface than those grown with ozone. The TiO₂:Co films with Co/(Co + Ti) cation ratio ranging from 0.01 to 0.30 were crystallized by annealing at 650 °C, possessing mixed phase composition comprising rutile and anatase and, additionally, CoTiO₃ or CoTi₂O₅. The annealed films demonstrated magnetic response expressed by magnetization curves with certain hysteresis and coercive fields.