Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Low-temperature growth and orientational control in RuO2 thin films by metal-organic chemical vapor deposition

For growth temperatures in the range of 275°C to 425°C, highly conductive RuO₂ thin films with either (110)- or (101)-textured orientations have been grown by metal-organic chemical vapor deposition (MOCVD) on both SiO₂/Si(001) and Pt/Ti/SiO₂/Si(001) substrates. Both the growth temperature and growth rate were used to control the type and degree of orientational texture of the RuO₂ films. In the upper part of this growth temperature range ( 350°C) and at a low growth rate (< 3.0 nm/min.), the RuO₂ films favored a (110)-textured orientation. In contrast, at the lower part of this growth temperature range ( 300°C) and at a high growth rate (> 3.0 nm/min.), the RuO₂ films favored a (101)-textured orientation. In contrast, higher growth temperatures (> 425°C) always produced randomly-oriented polycrystalline films. For either of these low-temperature growth processes, the films produced were crack-free, well-adhered to the substrates, and had smooth, specular surfaces. Atomic force microscopy showed that the films had a dense microstructure with an average grain size of 50–80 nm and a rms. surface roughness of 3–10 nm. Four-probe electrical transport measurements showed that the films were highly conductive with resistivities of 34–40 μΩ-cm (at 25°C).     

Structure and conducting properties of La0.5Sr0.5CoO3−δ films on YSZ

La_0.5Sr_0.5CoO_3−δ (LSCO) thin films were deposited on yttria stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell electrodes. During the deposition, the substrate temperature was varied from 450 to 750°C, and the oxygen pressure in the chamber was varied from 80 to 310 mTorr. Films deposited at 650°C and an oxygen background pressure of 150 mTorr were mostly (100) oriented. Deposition at higher temperatures or under lower oxygen pressures lead to mostly (110) oriented films. Films with low electrical resistivity of 10⁻³ Ω·cm were obtained.     

The effect of thermal annealing on aerosol-gel deposited SiO2 films: a FTIR deconvolution study

Aerosol-gel process has been used for the deposition of SiO₂ thin films. Layers were deposited from a solution with pH = 3.5 and water to TEOS molar ratio (rw) 2.2 and then treated at various temperatures ranging from room temperature to 700°C. As-prepared thin films have been characterized by FTIR spectroscopy. Spectra were acquired in transmission at 65° angle of incidence or at perpendicular incidence. Characteristic absorption bands of the SiO₂ sol-gel system have been studied with respect to the posttreatment temperature. Bands located at 1250–1000 cm⁻¹ and around 960 cm⁻¹ have been deconvoluted in several peaks. The origin and temperature dependence of these peaks are discussed.     

Deposition and dielectric properties of CaCu3Ti4O12 thin films on Pt/Ti/SiO2/Si substrates using pulsed-laser deposition

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates using pulsed-laser deposition technique. The crystalline structure and the surface morphology of the CCTO thin films were greatly affected by the substrate temperature and oxygen pressure. Thin films with a (2 2 0) preferential orientation were obtained at the substrate temperature above 700 °C and oxygen pressure above 13.3 Pa. The 480-nm thin films deposited under 720 °C and 26.6 Pa have a fairly high dielectric constant of near 2000 at 10 kHz and room temperature. The values of the dielectric constant and loss and their temperature-dependence under different frequency are comparable with those obtained in the epitaxial CCTO films grown on oxide substrates.     

Low temperature plasma-assisted oxidation and thin-film deposition processes for forming device-quality SiO2/Si and composite dielectric-SiO2/Si heterostructures

In the high-temperature thermal oxidation of Si, the SiO₂/Si interface is continuously regenerated as the bulk oxide grows. This paper describes an alternative low temperature, 200–300 °C, plasma-assisted process that optimizes electrical properties of SiO₂/Si interfaces and bulk SiO₂ layers by separately controlling interface formation and bulk oxide deposition. Composite dielectrics, oxide/nitride (ON) and oxide (ONO), have been fabricated by extending the low temperature plasma-assisted processes to include deposition of Si₃N₄ films. The electrical properties of SiO₂/Si structures formed by the two-step, low temperature oxidation-deposition process are essentially the same as those of SiO₂/Si structures formed by high temperature, 850–1050 °C, thermal oxidation. The electrical properties of devices incorporating ON and ONO composite dielectrics are degraded with respect to the SiO₂/Si structures, but are similar to those of composite dielectrics formed by combinations of high temperature processing.     

Segregation of Cu in Cu (Ti) alloys during nitridation in NH3

Cu(Ti 27 at.%) alloys on SiO₂ were reacted in NH₃ for 30 min over the temperature range 400–700 °C. Rutherford backscattering spectrometry in conjunction with high resolution transmission electron microscopy were utilized to investigate reaction products. At 400–450 °C, Ti is observed to segregate to the free surface to react with NH₃, forming an Ti oxynitride layer. Above 500 °C, Ti segregates to both the free surface and to the alloy/SiO₂ interface, leaving relatively-pure Cu layer. Reaction between Ti and SiO₂ results in a TiO/Ti₅Si₃ bilayer structure. By use of high spatial resolution energy dispersive X-ray spcctroscopy, the presence of a Cu-containing layer at the TiO/Ti₅Si₃ interface is observed. This layer may also contain Ti, Si and/or O. We propose a mechanism for Cu segregation to this interface which requires Cu diffusion across TiO and subsequent dissociation of Ti₅Si₃. Thermodynamic calculations support this mechanism.     

Preparation of Pt-PtOx thin films as electrode for memory capacitors

Pt-PtO_x thin films were prepared on Si(100) substrates at temperatures from 30 to 700°C by reactive r.f. magnetron sputtering with platinum target. Deposition atmosphere was varied with O₂/Ar flow ratio. The deposited films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Resistively of the deposited films was measured by d.c. four probe method. The films mainly consisted of amorphous PtO and Pt₃O₄ (or Pt₂O₃) below 400°C, and amorphous Pt was increased in the film as a deposition temperature increased to 600°C. When deposition temperature was thoroughly increased, (111) oriented pure Pt films were formed at 700°C. Compounds included in the films strongly depended on substrate temperature rather than O₂/Ar flow ratio. Electrical resistivity of Pt-PtO_x films was measured to be from the order of 10⁻¹ Ω cm to 10⁻⁵ Ω cm, which was related to the amount of Pt phase included in the deposited films.     

Epitaxial growth of RuO2 thin films by metal-organic chemical vapor deposition

Conductive RuO₂ thin films were epitaxially grown on LaAlO₃(100) and MgO(100) substrates by metal-organic chemical vapor deposition (MOCVD). The deposited RuO₂ films were crack-free, and well adhered to the substrates. The RuO₂ film is (200) oriented on LaAlO₃ (100) substrates at deposition temperature of 600°C and (110) oriented on MgO(100) substrates at deposition temperature of 350°C and above. The epitaxial growth of RuO₂ on MgO and LaAlO₃ is demonstrated by strong in-plane orientation of thin films with respect to the major axes of the substrates. The RuO₂ films on MgO(100) contain two variants and form an orientation relationship with MgO given by RuO₂(110)//MgO(100) and RuO₂[001]//MgO[011]. The RuO₂ films on LaAlO₃(100), on the other hand, contain four variants and form an orientation relationship with LaAlO₃ given by RuO₂(200)//LaAlO₃(100) and RuO₂[011]//LaAlO₃[011]. Electrical measurements on the RuO₂ thin films deposited at 600°C show room-temperature resistivities of 40 and 50 μΩ cm for the films deposited on the MgO and LaAlO₃ substrates, respectively.     

Low-temperature epitaxial growth of conductive LaNiO3 thin films by RF magnetron sputtering

Epitaxial growth of LaNiO₃ (LNO) thin films was successful on CeO₂/YSZ/Si(100), MgO(100) and SrTiO₃ (STO)(100) substrates by RF magnetron sputtering at 300 °C, although pulsed laser deposition requires 600 °C to prepare epitaxial LNO films according to the literature. Epitaxial LNO films deposited on CeO₂/YSZ/Si(100) and STO(100) had single orientation of LNO[100]//CeO₂[110]//YSZ[110]//Si[110]) and LNO[100]//STO[100], respectively. On the other hand, epitaxial LNO films deposited on MgO(100) had mixed orientations of LNO[100]//MgO[100] and LNO[100]//MgO[110]. The lattice parameter, composition and resistivity of the LNO thin films were strongly dependent on the substrate temperature. The minimum resistivity of LNO films was approximately 5×10⁻⁶ Ω m, which value almost agrees with the resistivity in the literature. It was found that the temperature to achieve minimum resistivity was 200 °C, irrespective of the type of substrate. The surface of the LNO films was smooth and flat.     

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

Atomic layer deposition growth of zirconium doped In2O3 films

Zirconium doped indium oxide thin films were deposited by the atomic layer deposition technique at 500 °C using InCl₃, ZrCl₄ and water as precursors. The films were characterised by X-ray diffraction, energy dispersive X-ray analysis and by optical and electrical measurements. The films had polycrystalline In₂O₃ structure. High transparency and resistivity of 3.7×10⁻⁴ Ω cm were obtained.     

Molecular beam epitaxial growth of SmBa2Cu3O7−δ thin films and effect of substrate temperature on the surface roughness

Stoichiometrically optimized, epitaxial SmBa₂Cu₃O_7-δ thin films with high T_{c, R = 0} and high critical current densities j_c have been prepared for the first time in a tightly controlled molecular beam epitaxy process in non-reactive molecular oxygen, followed by an in situ loading process with molecular oxygen. The surface roughness (on a submicrometre scale) of single-crystal films with their c axes perpendicular to the surface depends markedly on the surface temperature of the substrate during the deposition of the epitaxial films, within a range of only a few degrees centigrade. The calibrated optimal temperature for the preparation of epitaxial films 200 nm thick of this single orientation is found to be 680 ± 5 °C. In scanning tunnelling microscopy investigations, they show a surface roughness of less than 6 nm (five SmBa₂Cu₃O_7−δ unit cells) on a 2 μm × 2 μm scale. At deposition temperatures below this optimal deposition temperature, the well-known a-axis growth increases rapidly, whereas higher temperatures give a significantly higher surface roughness, which can be observed by scanning electron microscopy.     

Microwave dielectric properties of W-doped Ba0.6Sr0.4TiO3 thin films grown on (001) MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba_0.6Sr_0.4TiO₃ 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 °C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all films were post-annealed in 1 atm of oxygen at 1000 °C for 6 h. The dielectric Q (defined as 1 / tanδ) and the dielectric constant, ε_r, were measured at room temperature, at 2 GHz, using gap capacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as (ε_r(0 V) − ε_r(40 V)) / ε_r(0 V) × 100) and figure of merit (FOM) (defined as percent dielectric tuning × Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7 / 46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

Atomic-layer doping in Si by alternately supplied PH3 and SiH4

Atomic-layer doping of P in Si epitaxial growth by alternately supplied PH₃ and SiH₄ was investigated using ultraclean low-pressure chemical vapor deposition. Three atomic layers of P adsorbed on Si(100) are formed by PH₃ exposure at a partial pressure of 0.26 Pa at 450°C. By subsequent SiH₄ exposure at 220 Pa at 450°C, Si is epitaxially grown on the P-adsorbed surface. Furthermore, by 12-cycles of exposure to PH₃ at 300–450°C and SiH₄ at 450°C followed by 20-nm thick capping Si deposition, the multi-layer P-doped epitaxial Si films of average P concentrations of 10²¹ cm⁻³ are formed. The resistivity of the film is as low as 2.4×10⁻⁴ Ω cm. By annealing the sample at 550°C and above, it is found that the resistivity increases and the surface may become rough, which may be due to formation of SiP precipitates at 550°C and above. These results suggest that the epitaxial growth of very low-resistive Si is achieved only at a very low-temperature such as 450°C.     

Deposition of HfO2 thin films on ZnS substrates

HfO₂ thin films with columnar microstructure were deposited directly on ZnS substrates by electron beam evaporation process. SiO₂ thin films, deposited by reactive magnetron sputtering, were used as buffer layers, HfO₂ thin films of granular microstructure were obtained on SiO₂ interlayer by this process. X-ray diffraction patterns demonstrate that the as-deposited HfO₂ films are in an amorphous-like state with small amount of crystalline phase while the HfO₂ films annealed at 450 °C in O₂ for 30 min and in Ar for 150 min underwent a phase transformation from amorphous-like to monoclinic phase. Antireflection effect in certain infrared wave band, such as 3–6 μm, 4–12 μm, 4–8 μm and 3–10 μm, can be observed, which was dependent on the thickness of thin films. The cross-sectional images of HfO₂ films, obtained by field emission scanning electron microscopy, revealed that there was no distinct morphological change upon annealing.     

Structural characterization of TiNxOy/TiO2 single crystalline and nanometric multilayers grown by LP-MOCVD on (110)TiO2

TiO₂/TiN_xO_y superlattices were grown by Low Pressure-Metal-Organic Vapor Phase Epitaxy (LP-MOVPE) technique at deposition temperatures ranking from 650 to 750°C. The growth was performed on top of TiO₂(110) rutile substrates. Intense peaks observed in the X-rays rocking curves and θ-2θ diffraction patterns show the presence of crystalline epilayers. The TiN_xO_y layers were grown in a (200) cubic structure on the (110) quadratic TiO₂ epilayer structure. Transmission electron microscopy confirmed the XRD results and showed the formation of periodic and well structured epilayers.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Characterization of indium zinc oxide thin films prepared by pulsed laser deposition using a Zn3In2O6 target

Using a Zn₃In₂O₆ target, indium-zinc oxide films were prepared by pulsed laser deposition. The influence of the substrate deposition temperature and the oxygen pressure on the structure, optical and electrical properties were studied. Crystalline films are obtained for substrate temperatures above 200°C. At the optimum substrate deposition temperature of 500°C and the optimum oxygen pressure of 10⁻³ mbar, both conditions that indeed lead to the highest conductivity, Zn₃In₂O₆ films exhibit a transparency of 85% in the visible region and a conductivity of 1000 S/cm. Depositions carried out in oxygen and reducing gas, 93% Ar/7% H₂, result in large discrepancies between the target stoichiometry and the film composition. The Zn/In (at.%) ratio of 1.5 is only preserved for oxygen pressures of 10⁻²–10⁻³ mbar and a 93% Ar/7% H₂ pressure of 10⁻² mbar. The optical properties are basically not affected by the type of atmosphere used during the film deposition, unlike the conductivity which significantly increases from 80 to 1400 S/cm for a film deposited in 10⁻² mbar of O₂ and in 93% Ar/7% H₂, respectively.