Formation of crystalline aluminum silicate hydroxide layer during deposition of amorphous alumina coatings by electron beam evaporation

Aluminum oxide films were deposited on fused silica and borosilicate glass substrates by electron beam evaporation, without any substrate heating. Grazing incidence X-ray diffraction measurements found that a layer of crystalline aluminum silicate hydroxide was formed at the interface of the substrate and the amorphous alumina film, the latter transformed to γ-alumina phase on heat treatment at 800 °C. The aluminum silicate hydroxide layer was produced by the chemical reaction between condensing Al and Al–O species, OH⁻ from the residual water vapors in the chamber and Si atoms from the underlying silica and borosilicate glass substrates.     

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.     

Investigation of the aluminum oxide/Si(1 0 0) interface formed by chemical vapor deposition

Thin films of aluminum oxide were deposited using trimethylaluminum and oxygen. The deposition rate was found to decrease with increasing temperature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the film/substrate interface. When dry O₂ was used during deposition, the film/substrate interface was free of any silicon dioxide or aluminum silicate phase. On annealing the as-deposited films in Ar, a layer of silicon dioxide film formed at the interface. XPS results indicated that the O/Al ratio in the as-deposited films was higher than that in stoichiometric Al₂O₃. However, the ratio was found to decrease in the annealed samples suggesting that excess oxygen present in the deposited films is responsible for the formation of interfacial silicon dioxide layer. Interfacial phase formation was observed in the as-deposited samples, when small amounts of ozone along with oxygen were used as the oxygen precursor.     

Properties of aluminum oxide thin films deposited by pulsed laser deposition and plasma enhanced chemical vapor deposition

The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 °C on (100) Si and Si-SiO₂ substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas γ type nano-crystallized structures are pointed out for films deposited at 800 °C. A dielectric constant of ∼ 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 °C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields.     

Photoemission studies of the initial interface formation of ultrathin MgO dielectric layers on the Si(111) surface

This study investigates the interface formation between a magnesium oxide dielectric overlayer and an ultrathin SiO₂ layer (∼ 0.3 nm) grown on the atomically clean p-type Si(111) surface in ultra high vacuum. Both soft X-ray synchrotron radiation based photoemission and conventional X-ray photoelectron spectroscopy have been used to characterise the evolution of the interface and monitor the change in the interfacial oxide thickness. As the MgO film grows, there is an increase in the intensity of the silicon oxide features indicating the growth of the interfacial oxide which saturates at a thickness of approximately 0.7 nm. Spectra acquired at the surface sensitive 130 eV photon energy, reveal the emergence of a chemically shifted component on the low binding energy side of the substrate peak which is attributed to atomic displacement of silicon atoms from the substrate to the interfacial oxide at room temperature. This evidence of atomic disruption at the high dielectric constant material (high-κ) and silicon interface would be expected to contribute to charge carrier scattering mechanisms in the silicon and could account for the generally observed mobility degradation in high-κ stacks. Thermal annealing studies of deposited MgO films show that dissociation begins to occur above 600 °C with desorption of Mg and the growth of a silicon oxide.     

Electrical characterization of amorphous silicon carbide thin films deposited via polymeric source chemical vapor deposition

Polymeric source chemical vapor deposition (PS-CVD) was used to synthesize amorphous silicon carbide (a-SiC) thin films. The PS-CVD process was conducted at temperatures between 750 and 1000 °C. The substrates used were silicon single crystal wafers of p-type and n-type, and thermally grown silicon dioxide substrates. The chemical and electrical properties of the films were studied by various techniques, including Fourier transform infrared spectroscopy, elastic recoil detection (ERD), and capacitance-voltage technique. A correlation was observed between the average concentration of oxygen in the films and the deposition temperature, linking a low oxygen concentration to a high deposition temperature. However, the concentration of oxygen in the films deposited at the same temperature is independent of the substrate. The thin films deposited at low temperature showed insulating behaviour, while the semiconducting behaviour is obtained at high deposition temperatures. Ohmic contacts were obtained on the deposited semiconductor thin film by evaporating nickel contacts, followed by annealing of the sample at 800 °C for 2 min.     

X-ray absorption spectroscopy study of thermally annealed Cu–Al–O thin films

Cu–Al–O thin films are deposited on (0001) sapphire substrates by radio-frequency sputtering using an Al–Cu mosaic target. The Cu/Al atomic ratio of as-deposited Cu–Al–O films is measured to be 1.1. After deposition, the Cu–Al–O films are annealed at 600, 800, and 1000 °C, respectively, for 1 h in a N₂ atmosphere. The film crystal structure, electronic structure, valence band, and electrical properties are studied. The as-deposited films are amorphous and films annealed at 600 °C contain the crystallized CuO phase; the structure becomes crystallized CuAlO₂ after annealing at 800 °C and 1000 °C. The 800 °C annealed film grows along the (00l) plane. The crystallization decreases with the growth of the (012) and (018) planes for films annealed at 1000 °C. The resistivity values of the 800 °C and 1000 °C annealed films were measured as 1.07 Ω-cm and 864.01 Ω-cm, respectively. The lower resistivity of the 800 °C annealed film is attributed to preferred (00l) growth orientation and a reduction of the energy band gap.     

Catalytic chemical vapour deposition synthesis of carbon spheres

Carbon spheres (CSs) were successfully grown in the presence of cobalt-silicon-mesoporous aluminum silicate (Co-Si-MAS) by chemical vapour deposition (CVD) using C₂H₂ as the source of carbon at 850 °C. The Co-Si-MAS catalysts with Si/Al molar ratios of 25, 50, 100 and 150 were synthesized by sol-gel preparation and followed by anchoring process. The scanning electron microscopy (SEM), transmission electron microscopy (TEM) images and Raman spectroscopy experiments showed that the obtained CSs possess nearly perfect spheres with diameters range from 650 to 1000 nm. It was found that CSs were fabricated under a thin film that was deposited during the catalytic reaction. On the basis of qualitative analysis it was revealed that the film included cobalt, silicon and aluminum elements. This thin film was applied as a catalyst for the synthesis of CSs.     

Attribution of white-light emitting centers with carbonized surface in nano-structured SiO2:C layers

Carbon incorporated silicon oxide layers were fabricated by carbonization of porous silicon layer in acetylene atmosphere followed by oxidation in wet argon. The resulting porous SiO₂:C material exhibited a strong white photoluminescence. Subsequent thermal treatment in oxygen at 600 °C significantly decreased the green-yellow part of photoluminescence band while blue shoulder remained unchanged. Annealing at the same temperature in pure argon did not change light-emission properties indicating that the green-yellow light-emission sites originate from the surface. This study focuses on the interface of silicon oxide matrix and carbon inclusions by high-resolution scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). It is confirmed by EELS and STEM that the green-yellow emission band is associated with the carbonized interface in the porous layer.     

Properties of plasma enhanced chemical vapor deposited silicon nitride for the application in multicrystalline silicon solar cells

Hydrogenated films of silicon nitride (SiNx:H) were investigated by varying the deposition condition in plasma enhanced chemical vapor deposition (PECVD) reactor and annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in multicrystalline silicon solar cells. By varying the gas ratio (ammonia to silane), the silicon nitride films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, silicon wafer with the film deposited at 450 °C showed the best minority carrier lifetime. The film deposited with the gases ratio of 0.57 showed the best peak of carrier lifetime at the annealing temperature of 800 °C. The performance parameters of cells fabricated by varying co-firing peak temperature also showed the best values at 800 °C. The multicrystalline silicon (mc-Si) solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrate (125 mm × 125 mm) was found to have the conversion efficiency of 15%.     

Efficiency improvement of multicrystalline silicon solar cells after surface and grain boundaries passivation using vanadium oxide

The aim of this work is to investigate the effect of vanadium oxide deposition onto the front surface of multicrystalline silicon (mc-Si) substrat, without any additional cost in the fabrication process and leading to an efficient surface and grain boundaries (GBs) passivation that have not been reported before. The lowest reflectance of mc-Si coated with vanadium oxide film of 9% was achieved by annealing the deposited film at 600 °C. Vanadium pentoxide (V₂O₅) were thermally evaporated onto the surface of mc-Si substrates, followed by a short annealing duration at a temperature ranging between 600 °C and 800 °C, under O₂ atmosphere. The chemical composition of the films was analyzed by means of Fourier transform infrared spectroscopy (FTIR). Surface and cross-section morphology were determined by atomic force microscope (AFM) and a scanning electron microscope (SEM), respectively. The deposited vanadium oxide thin films make the possibility of combining in one processing step an antireflection coating deposition along with efficient surface state passivation, as compared to a reference wafer. Silicon solar cells based on untreated and treated mc-Si wafers were achieved. We showed that mc-silicon solar cells, subjected to the above treatment, have better short circuit currents and open-circuit voltages than those made from untreated wafers. Thus, the efficiency of obtained solar cells has been improved.     

Conformal aluminum oxide coating of high aspect ratio structures using metalorganic chemical vapor deposition

The metalorganic chemical vapor deposition of aluminum oxide has been studied over a wide process parameter range. Electrical properties of as-grown and annealed layers have been investigated using planar aluminum/aluminum oxide/silicon capacitors. The best processing conditions resulted in a leakage current of 10 nA/cm² at an equivalent oxide thickness of 3.6 nm. In addition, the film conformality was evaluated on silicon trench structures with aspect ratios of up to 60. Excellent step coverage of over 90% (thickness at trench bottom to thickness at trench middle) was achieved at temperatures below 400 °C and a pressure of 100 Pa. After annealing the electrical properties of these layers, analyzed on planar test structures, were comparable to the results obtained at higher deposition temperature.     

Structural evolution of La-Cr-O thin film: Part II. Elasto-plastic properties by nanoindentation

The goal of this research is to study the elasto-plastic properties of La-Cr-O thin films deposited by RF-magnetron sputtering on stainless steel interconnect materials after annealing at high temperatures in air. Elastic modulus, hardness and yield pressure derived from nanoindentation data are reported for thin films in different structural states. The amorphous film has an estimated elastic modulus of 174 GPa. The moduli of annealed films are calculated to be 150, 185 and 120 GPa after annealing at 500 °C, 600 °C and 800 °C, respectively. The film annealed at 800 °C has the lowest hardness and is dramatically different from the other structural states due to formation of the nanoporosity. The amorphous film and the films annealed at 500 °C and 600 °C both have hardness of 14 GPa, which is close to the value estimated by modeling.     

Infrared and raman spectroscopic studies of optically transparent zirconia (ZrO2) 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.     

Microstructural and electrical characteristics of rapidly annealed Ni/Mo Schottky rectifiers on cleaned n-type GaN (0001) surface

We have investigated the electrical and microstructural properties of Ni/Mo Schottky rectifiers to n-type GaN by current–voltage (I–V) and transmission electron microscopy (TEM) before and after annealing at 600 °C. The obtained barrier height for as-deposited Ni/Mo contact is 0.66 eV. It is observed that the barrier height increases with annealing temperature up to 500 °C, reaching a maximum value of 0.75 eV at this temperature. However, the Schottky barrier height of the Ni/Mo Schottky contact slightly decreased to 0.67 eV (I–V) when the contact was annealed at 600 °C. According to the HRTEM, STEM and EDX analysis, the formation of Ga-Ni interfacial layer at the interface results in the accumulation of gallium vacancies near the surface of the GaN layer. This could be the reason for increase in barrier heights upon annealing at elevated temperatures. The variation in the measured barrier height after annealing at 600 °C may be due to the formation of native oxide layer at the interface compared to the 500 °C annealed contact.     

Characteristics of high-k gate oxide prepared by oxidation of multi-layered Hf/Zr/Hf/Zr/Hf metal films

We investigated the physical and electrical properties of Hf-Zr mixed high-k oxide films obtained by the oxidation and annealing of multi-layered metal films (i.e., Hf/Zr/Hf/Zr/Hf, ∼ 5 nm). We demonstrated that the oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf-Zr mixed oxide film was formed on the top of silicate film due to inter-diffusion between Hf and Zr layer. This film shows the improved dielectric constant (k) and the raised crystallization temperature. Compared with HfO₂ and ZrO₂ gate dielectric, the crystallization temperature of Hf-Zr mixed oxides was raised by more than 200 °C. Using AES and XPS, we observed that Zr oxide has more fully oxidized stoichiometry than Hf oxide, irrespective of annealing temperatures. We also found that the thickness of an interfacial layer located between Hf-Zr mixed oxide and Si substrate also increases as annealing temperature increases. Especially, the thin SiO_x interfacial layer starts to form if annealing temperature increases over 700 °C, deteriorating the equivalent oxide thickness.     

High-temperature growth and in-situ annealing of MgZnO thin films by RF sputtering

We report the effect of growth temperature and annealing on microstructural, elemental and emission properties of as-grown and in-situ annealed MgZnO thin films, containing ∼ 10 at. % Mg, grown at high temperature by RF sputtering. Microstructural analysis carried out by TEM reveals formation of thin oxide layer with increased layer thickness on growth temperature, in the interface between Si substrate and MgZnO thin film. Irrespective of growth temperature, increase in Mg mole fraction with increase in thickness of MgZnO thin film is observed from EDX and AES spectroscopy, and a maximum of 14 at. % Mg is observed at 800 °C. The photoluminescence investigation shows blue shift of 104 meV in MgZnO film grown at 800 °C, compared to the film grown at 600 °C, which is due to the enhancement of the Mg incorporation at higher temperature. In addition, annealing at the growth temperature enhanced the intensity ratio of the UV/deep level emission and increased the grain size. Thermal treatment in a vacuum improved the emission efficiency and changed the origin of the point defects.     

Influence of annealing temperature on the structural, mechanical and wetting property of TiO2 films deposited by RF magnetron sputtering

TiO₂ films have been deposited on silicon substrates by radio frequency magnetron sputtering of a pure Ti target in Ar/O₂ plasma. The TiO₂ films deposited at room temperature were annealed for 1 h at different temperatures ranging from 400 °C to 800 °C. The structural, morphological, mechanical properties and the wetting behavior of the as deposited and annealed films were obtained using Raman spectroscopy, atomic force microscopy, transmission electron microscopy, nanoindentation and water contact angle (CA) measurements. The as deposited films were amorphous, and the Raman results showed that anatase phase crystallization was initiated at annealing temperature close to 400 °C. The film annealed at 400 °C showed higher hardness than the film annealed at 600 °C. In addition, the wettability of film surface was enhanced with an increase in annealing temperature from 400 °C to 800 °C, as revealed by a decrease in water CA from 87° to 50°. Moreover, the water CA of the films obtained before and after UV light irradiation revealed that the annealed films remained more hydrophilic than the as deposited film after irradiation.     

Annealing effects on microstructure and mechanical properties of sputtered multilayer Cr(1 − x)AlxN films

Multilayer Cr_(1 − x)Al_xN films with a total thickness of 2 μm were deposited on high-speed steel by medium frequency magnetron sputtering from Cr and Al-Cr (70 at.% Al) targets. The samples were annealed in air at 400 °C, 600 °C, 800 °C and 1000 °C for 1 hour. Films were characterized by cross-sectional scanning electron microscopy and X-ray diffraction analysis. The grain size of the as-deposited multilayer films is about 10 nm, increasing with the annealing temperature up to 100 nm. Interfacial reactions have clearly changed at elevated annealing temperatures. As-deposited films' hardness measured by nanoindentation is 22.6 GPa, which increases to 26.7 GPa when the annealing temperature goes up to 400 and 600 °C, but hardness decreases to 21.2 GPa with further annealing temperature increase from 600 to 1000 °C. The multilayer film adhesion was measured by means of the scratch test combined with acoustic emission for detecting the fracture load. The critical normal load decreased from 49.7 N for the as-deposited films to 21.2 N for the films annealed at 1000 °C.     

Annealing optimization of silicon nitride film for solar cell application

Hydrogenated films of silicon nitride (SiNx:H) is commonly used as an antireflection coating as well as passivation layer in crystalline silicon solar cell. SiNx:H films deposited at different conditions in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor were investigated by varying annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in silicon solar cells. By varying the gases ratio (R = NH₃/SiH₄ + NH₃) during deposition, the SiNx:H films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, the silicon wafer with SiNx:H film deposited at 450 °C showed the best effective minority carrier lifetime. The film deposited with the gases ratio of 0.57 shows the best peak of carrier lifetime at the annealing temperature of 800 °C. The single crystalline silicon solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrates (125 mm × 125 mm) were found to have the conversion efficiencies as high as 17.05 %. Low cost and high efficiency single crystalline silicon solar cells fabrication sequence employed in this study has also been reported in this paper.