As-deposited Amorphous Films Research Articles

Effect of rapid thermal annealing on the structural and electrical properties of TiO2 thin films prepared by plasma enhanced CVD

Titanium oxide thin films were deposited on p-type Si(100), SiO2/Si, and Pt/Si substrates by plasma enhanced chemical vapor deposition using high purity Ti(O-i-C3H7)4 and oxygen. As-deposited amorphous TiO2 thin films were treated by rapid thermal annealing (RTA) in oxygen ambient, and the effects of RTA conditions on the structural and electrical properties of TiO2 films were studied in terms of crystallinity, microstructure, current leakage, and dielectric constant. The dominant crystalline structures after 600 and 800 ‡C annealing were an anatase phase for the TiO2 film on SiO2/Si and a rutile phase for the film on a Pt/Si substrate. The dielectric constant of the as-grown and annealed TiO2 thin films increased depending on the substrate in the order of Si, SiO2/Si, and Pt/ Si. The SiO2 thin layer was effective in preventing the formation of titanium silicide at the interface and current leakage of the film. TEM photographs showed an additional growth of SiOx from oxygen supplied from both SiO2 and TiO2 films when the films were annealed at 1000 ‡C in an oxygen ambient. Intensity analysis of Raman peaks also indicated that optimizing the oxygen concentration and the annealing time is critical for growing a TiO2 film having high dielectric and low current leakage characteristics.

Experimental and theoretical investigations of laser-induced crystallization and amorphization in phase-change optical recording media

We describe the numerical procedure for calculating three-dimensional profiles of temperature in a multilayer stack illuminated by a laser beam, and model the crystallization and amorphization kinetics for phase-change rewritable media. Experimental methods have been used to determine indirectly the probabilities of nucleation and growth for Ge2Sb2Te5 alloy. Some of the fundamental behaviors of phase-change erasable media, such as the crystallization of as-deposited amorphous phase, amorphization of supercooled liquid, and recrystallization of quenched amorphous phase, have been illustrated based on our three-dimensional temperature calculations and the model kinetics. The calculated transient reflectance behavior of as-deposited Ge2Sb2Te5 amorphous films in a single layer and in a quadrilayer stack, as well as the erasure behavior of Ge2Sb2Te5 alloy in a quadrilayer disk are in good agreement with experimental observations.

Effect of the starting amorphous structure on the solid-phase crystallization of silicon

Abstract The effect of the deposition rate of amorphous silicon films grown by low-pressure chemical vapour deposition on the quality of furnace-crystallized films is studied. Numerous physical, optical and electrical characterization techniques have been used. The use of the X-ray diffraction technique in the study of polycrystalline silicon microstrains is particularly presented. Results show that, the higher the deposition rate, the higher is the quality of the polycrystalline silicon obtained. This quality is obtained near the limiting rate above which powder formation begins. This quality may be explained by the microstructure of the as-deposited amorphous films and in particular by the role of the low hydrogen content which delays the nucleation and increases the subsequent crystallization rate.

Phase transformations in sputtered thin films of Tix(Ni, Cu)1−xII: Displacive transformations

Abstract Part I of this series described diffusional transformations in sputtered films of Ti x (NiCu)1−x containing about 5 at.% Cu. The as-deposited amorphous films supported substantial supersaturation either of Ti or of Ni + Cu at 300 K. Subsequent isothermal annealing produced fine oriented precipitates which altered the matrix chemistry and often exerted long-range stress fields arising from coherency strains. These phenomena will be shown in part II to influence strongly the subsequent displacive transformation behaviour. In Ti47.4Ni46.5Cu6.1 films, precipitates of (NiCu)2 Ti2 resulted in B2←R and R←B19′ transformations. Extensive precipitation of Ti2(Ni, Cu) in Ti51.0Ni44.4Cu4.6 films led to formation of an orthorhombic martensite, with preferred [010]B19‖[011]B2 and (202)B19‖(211)B2 orientation relationships, prior to transformation to a monoclinic phase that formed along alternating {322}B2 and {112}B2 steps. Even in films with compositions near stoichiometry. small quantities of transgranular Ti40Ni56.5Cu3.5 and Ti2(NiCu) precipitates significantly influenced transformation sequences, temperatures and details of martensite crystallography.

Structure and ferroelectric properties dependence on thermal treatment of modified lead titanate thin films

Calcium modified lead titanate thin films have been prepared from a sol-gel method. Different thermal conditions have been used for the crystallization of the as-deposited amorphous films. The influence of thermal treatment on the perovskite structure and strain of the films is studied by a grazing incidence X-ray diffraction technique (GIXRD). The ferroelectric response of the films is related to their crystalline structure and chemical composition.

Rapid Thermal Magnetic Annealing: A Novel Technique in Thin-Film Recording Head Production?

AbstractA new emerging application area for Rapid Thermal Annealing (RTA) may be in the manufacturing of thin-film recording heads for high-density (hard disk drive, video, audio and data tape) recording. To that end we co-designed a new commercial reactor with an external electromagnet to anneal thin soft-magnetic films (nanocrystalline iron alloys) deposited on ceramic wafers of up to 150 mm diameter. The electromagnet generates a field controllable up to 660 Oe (52.8 kA/m). It is completely homogeneous in direction (i.e. fully parallel field lines) across the entire wafer area. Wafers can be annealed either statically, or while rotating (up to 120 rpm), or in two subsequent heating steps with a 90° wafer rotation in between.Nanocrystalline Fe-Nb-Si-N layers have better soft-magnetic properties after Rapid Thermal Magnetic Annealing (RTMA) in a static magnetic field than after conventional furnace annealing in a static field. Temperature-programmed resistance measurements and Transmission Electron Microscopy (TEM) show that the first nanocrystalline, body-centered cubic iron grains start growing already as of 350 °C from the amorphous as-deposited film, whereas the desired segregation of NbN starts only as of 530°C. RTA can be used to promote the kinetics of the segregation of NbN along the boundaries of nanocrystalline iron nuclei. This prevents the iron grains from further growth: with RTMA the iron alloys show smaller nanocrystalline iron particles (order: 10 nm) as observed by TEM.

Effect of γ-irradiation on the optical and electrical properties of amorphous InSe thin films

Abstract The influence of γ-irradiation on the optical and electrical properties of amorphous InSe thin films was investigated. Optical absorption coefficient (α) of amorphous InSe thin films was represented as a function of photon energy (hμ) and the data were used to deduce the value of the optical energy gap (Eg opt), the refractive index (n) and the valence band density of states (gi) of the films. The analysis of the absorption coefficient data revealed the existence of indirect transition with optical energy gap Eg opt = 0.98 eV for as-deposited (unirradiated) amorphous InSe films, which increases to 1.15 eV with increasing the γ-doses to 2.5 Mrad. It was found that the activation energy ΔE obtained form the temperature dependence of conductivity for unirradiated and irradiated amorphous InSe films increases and the conductivity decreases with increasing γ-doses. Also it was found that the degree of disorder and defects in the amorphous structure changes due to γ-irradiation.

Effect of Electrodes on Crystallization and Electrical Properties of Ferroelectric Pzt Films Deposited by Rf Magnetron Sputtering

AbstractThe electrical properties and crystallization process of Pb(Zr0.4, Ti0.6)O3or PZT thin films grown by rf magnetron sputtering, from ceramic target, on fiber-textured (111)Pt/TiN/Ti/SiO2/Si and polycrystalline RuOx/SiO2/Si have been studied. It is found that the amorphous as-deposited thin film, processed by rapid thermal annealing (RTA), is transformed to a perovskite PZT at about 700°C. It is pointed out that the “heating rates” to reach 700°C affect the electrical properties of such films: TEM analysis reveal different grain sizes as a function of the heating rate. The XRD show that an oriented (111) PZT is promoted when the film is annealed to the temperatures of 800°C for 5 secondes. For these annealing conditions, the electrical properties of such structure depend strongly on the deposition conditions of PZT. Our process studies show that a thin film PZT deposited on Pt or RuO1.65at 200°C and 1 Pa argon pressure gives good hysteresis loop with high values of Ps and Pr (about 20 and 30 μC/cm2on Pt and RuO1.65respectively) and low leakage current about 10−11A/cm2on Pt and 10−6A/cm2on RuO1.65.

Pyrochlore-perovskite phase development of sol-gel derived modified lead titanate thin films

Calcium modified lead titanate thin films were deposited by spin-coating from sol-gel derived solutions. The as-deposited amorphous films were thermally treated to crystallize the perovskite. In order to get information about the crystallization mechanism of these films, experiments were conducted with different annealing conditions. A depth profile study of the (Ca,Pb)TiO 3 films was made grazing incidence X-ray diffraction analysis. The results confirmed the coexistence of a ferroelectric phase (perovskite) and nonferroelectric phases (pyrochlore type, deficient in lead and/or oxygen) in the crystallized films. The formation and stability of these secondary phases seem to be related with the opportunity of producing lead and oxygen losses during thermal treatment. Thus, samples prepared under different conditions showed different pyrochlore/perovskite ratios. Quite different hysteresis loops are measured in the films prepared with different thermal conditions indicating that the ferroelectric response is directly affected by the defects and crystalline phases developed in the films.

GaGeTe films as phase-change optical recording media

Ga 20Ge 30Te 50 thin films deposited by vacuum evaporation on various substrates have been studied for their structural and optical properties. The as-deposited amorphous films were crystallized by thermally annealing them. The optical constants of the amorphous films indicate semiconducting behaviour ( n > k). The optical bandgap ( E g) determined from Tauc's plot is 0.7 eV. The change in reflectance on crystallization has been utilized to obtain maximum optical contrast by optimising the thickness of the film.

Microstructural and magnetic studies of granular GdW films

We have studied the microstructural and magnetic properties of sputtered nanocrystalline granular Gd-W thin films as a function of annealing temperature. Granular Gd-W films were formed by annealing the as-deposited amorphous films in the temperature range 700–950 °C for 15 min. The TEM studies on the annealed samples indicate that the Gd and W phases crystallize as separate phases around 825 °C. The grain sizes of these granular phases were estimated to be about 10–30 nm. Magnetic measurements of samples annealed at 875 °C indicate the coexistence of superparamagnetic Gd with a blocking temperature near 50 K and ferromagnetic Gd with a Curie temperature near 293 K. Higher temperature annealings led to bulk-like ferromagnetic Gd behavior.

Co-sputtered TiB 2 as a diffusion barrier for advanced microelectronics with Cu metallization

Titanium boride thin films were deposited from separate Ti and B targets by magnetron co-sputtering and the conditions for obtaining good diffusion barrier properties were evaluated. The best diffusion barrier properties against Cu penetration were obtained when the film was amorphous and deposited with RF bias. Auger electron spectroscopy (AES) and plan-view scanning electron microscopy (SEM) revealed that Cu penetration into amorphous titanium boride is appreciably greater in the unbiased specimen. The as-deposited amorphous film has a resistivity of 450–500 μΩ · cm, but after following annealing at ∼ 723°C for 1 h a substantial decrease in resistivity was obtained while the structure of the boride remained amorphous. The amorphous boride is stable up to 890°C. The crystallization temperature can be decreased by RF bias application, and under these conditions microcrystalline TiB 2 can be formed already at ∼ 400°C. Crystalline TiB 2 has a strong (001) preferred orientation. TiSi 2 (C-54) is also formed during annealing at temperatures exceeding 765°C as a result of the reaction of titanium boride containing free Ti with the silicon substrate.

Low pressure chemical vapour deposition of tantalum pentoxide thin layers

Tantalum pentoxide thin films were grown by a low pressure chemical vapour deposition process using a metalorganic tantalum precursor material. After characterizing the deposition process, the stoichiometry, structure and electrical properties of the tantalum oxide thin films were investigated before and after annealing in oxygen and nitrogen at various temperatures. At annealing temperatures higher than 700°C, the as-deposited amorphous film becomes polycrystalline. Refractive index, dielectric permittivity and leakage current behaviour are improved by this phase transition.

Alternating sputtered Al-Mo deposits and their interaction with a Au top layer

Al-Mo deposits were prepared with alternating sputtering using separate Al and Mo targets. The relative compositions of the binary films were found to be linearly proportional to the Al Mo power ratio. The microstructure, detected with X-ray diffraction, of the as-deposited films were observed to be the Al, Mo and amorphous phases, depending on the relative atomic ratio of Al Mo . Transmission electron microscopy diffraction patterns indicated that the films were not uniform in structure. The crystallization behavior of the amorphous deposits was found to be influenced by the Al Mo atomic ratio of the deposit. A higher Al content lowered the crystallization temperature of the deposits. The as-deposited amorphous films reacted with a Au top layer right upon deposition. However, the conversion of the Al-Mo deposits to a corresponding compound will raise the interaction temperature.

Thin-film Li-LiMn<sub>2</sub>O<sub>4</sub> batteries

Thin-film rechargeable Li-LiMn 2 O 4 batteries have been fabricated and characterized. Following deposition by electron beam evaporation of LiMn 2 O 4 , the amorphous as-deposited cathode films 1 cm 2 in area by 0.3to 4-μm thick were annealed at 700/spl deg/C to 800/spl deg/C in oxygen in order to form the crystalline spinet phase. The specific capacity of the cells between 4.5 V to 3.8 V ranged from 50 μAh/mg to 120 μAh/mg. When cycled over this range, the batteries exhibited excellent secondary performance with capacity losses as low as 0.001% per cycle. On charging to 5.3 V, a plateau with a median voltage of 5.1 V was observed. The total charge extracted between 3.8 V to 5.3 V corresponded to about 1 Li/Mn 2 O 4 .

Phase evolution and annealing effects on the electrical properties of Pb(Zr 0.53Ti 0.47)O 3 thin films with RuO 2 electrodes

The electrical properties and crystallization of Pb(Zr 0.53Ti 0.47)O 3 (PZT) thin films grown on RuO 2 electrodes by the sol-gel process have been studied. It was found that the amorphous as-deposited thin film first transforms to a pyrochlore phase at 500 °C. On further annealing, perovskite PZT begins to crystallize at about 600 °C. TEM anlysis reveals that a pyrochlore-type second phase still exists in the films even after annealing to temperatures of 750 °C for 10 min. These PZT films are fatigue-free, but they show large property variation and high leakage currents ( J = 10 −3Acm −2 at 1 V). An 800 °C annealing treatment, for 10 min in air of the RuO 2 bottom electrode prior to film deposition enhanced perovskite PZT nucleation, thereby eliminating the pyrochlore-type second phase. In addition, the leakage currents of PZT films grown on annealed RuO 2 electrodes are about two orders of magnitude lower than those of PZT films grown on unannealed RuO 2. It is also observed that annealing the entire capacitor stack after the top electrode deposition improved capacitor properties.

Laser Crystallization and Annealing of Ferroelectric Thin Films

ABSTRACTFerroelectric PbZr0.44Ti0.56O3 film with pure ferroelectric phase was fabricated by Ar3+ and KrF laser crystallization technique from as-deposited amorphous films, with the substrate at room temperature. Laser annealing technique was also used to improve the quality of BaTiO3 (BT) films.

Structure and electrical transport in microcrystalline composite Si-NiSi 2 thin films

The thermally activated conductivity behavior in microcrystalline composite Si-NiSi 2 thin films depends significantly on their microstructure. Incorporated Ni atoms with concentrations from 0.2 to 1 at.% in as-deposited amorphous silicon thin films induce a crystallization process during thermal annealing. For concentrations below 0.5 at.% the Ni atoms precipitate in NiSi 2 crystals which induce a needle-like growth of Si crystallites in the amorphous matrix. In the following process strain-induced effects lead to a transition from the amorphous to a microcrystalline matrix. For Ni concentrations of 0.5 at.% and above the crystallization leads to a homogeneous microcrystalline phase. In both cases the electric transport is found to be due to combined grain boundary states.

Rare-earth-doped transparent yttrium silicate thin film phosphors for colour displays

We report the preparation and cathodoluminescent properties of rare-earth-doped Y2O3SiO2 thin films. The thin films were prepared by magnetron sputtering. By doping with Eu3+, Tb3+ and Ce3+, most as-deposited amorphous thin films show luminescence. High temperature annealing above 800 °C increases the luminescence intensity 5–10 times. This reveals that the crystal field is dominated by the nearest atomic neighbours. The primary colours needed for a full-colour display can be realized by doping with Eu3+, Tb3+ and Ce3+.

Fabrication of amorphous Sb 2S 3 films by chemical deposition

A simple, non-polluting and economical electrodeless chemical deposition technique for fabricating amorphous Sb 2S 3 films on glass or clear polymer substrates is described. The technique is based on hydrolytic decomposition of antimony thiosulfate compounds in aqueous media and is convenient for large area depositions at room temperature. Glassy, transparent and uniform amorphous films with yellow to orange colors were produced. The terminal thickness of the films from a single bath was ∼ 0.4 μm. The X-ray diffractograph of the annealed films showed that orthorhombic Sb 2S 3 crystallizes within the amorphous phase upon annealing in air at 170–220°C for several hours. The optical band-gap of as-deposited amorphous films and annealed, partially crystallized films were found to be 2.48 ± 0.02 eV and 1.80 ± 0.02 eV, respectively. The sheet resistance of 0.1–0.4 μm thick amorphous films was of the order of 10 12 Ω/square and two orders of magnitude less for the annealed films. Post-deposition immersion of the films in aqueous AgNO 3 solutions decreased the resistance by up to five orders of magnitude.