Planar chalcogenide quarter wave stack filter for near-infrared

A quarter wave stack dielectric filter with normal incidence pass band in near-infrared range was prepared from alternating high index contrast chalcogenide films. The prepared filter consists of a low index Ge–S spacer layer surrounded by two 4.0 pairs Sb–Se/Ge–S reflectors. Films were deposited using flash and thermal evaporation techniques. After deposition, the filter was annealed at 165 °C for 1 h. Optical reflectivity measurements of the annealed filter revealed a ～63% normal incidence passband near 1540 nm. An ～80% passband was recorded after illumination of the filter by the light with s-polarization at angles 35°, 45° and 55°, while its position shifted to 1451, 1476 and 1505 nm, respectively. A ～75% passband appeared near 1436, 1467 and 1498 nm in response to illumination of the filter by the light with p-polarization at the same angles. The angular dependence of the reflectivity of dielectric multilayer can be exploited for filtering of incident light.     

Crystallization of bismuth titanate and bismuth silicate grown as thin films by atomic layer deposition

Bismuth silicate and bismuth titanate thin films were deposited by atomic layer deposition (ALD). A novel approach with pulsing of two Bi-precursors was studied to control the Si/Bi atomic ratio in bismuth silicate thin films. The crystallization of compounds formed in the Bi₂O₃–SiO₂ and Bi₂O₃–TiO₂ systems was investigated. Control of the stoichiometry of Bi–Si–O thin films was studied when deposited on Si(1 0 0) and crystallization was studied for films on sapphire and MgO-, ZrO₂- and YSZ-buffered Si(1 0 0). The Bi–Ti–O thin films were deposited on Si(1 0 0) substrate. Both Bi–Si–O and Bi–Ti–O thin films were amorphous after deposition. Highly a-axis oriented Bi₂SiO₅ thin films were obtained when the Bi–Si–O thin films deposited on MgO-buffered Si(1 0 0) were annealed at 800 °C in nitrogen. The full-width half-maximum values for 200 peak were also studied. An excess of bismuth was found to improve the crystallization of Bi–Ti–O thin films and the best crystallinity was observed with Ti/Bi atomic ratio of 0.28 for films annealed at nitrogen at 1000 °C. Roughness of the thin films as well as the concentration depth distribution were also examined.     

Copper nitride (Cu3N) thin films deposited by RF magnetron sputtering

The copper nitride thin films were prepared on glass substrate by RF magnetron sputtering method. At pure nitrogen atmosphere, the nitrogen flow rate affects the copper nitride thin films’ structures. Only a little part of nitrogen atoms insert into the body center of Cu₃N structure and parts of nitrogen atoms insert into Cu₃N crystallites boundary at higher nitrogen flow rate. But the indirect optical energy gap, E_opg, decreases with increasing nitrogen flow rate. The typical value of E_opg is 1.57 eV. In a nitrogen and argon mixture atmosphere, when the nitrogen partial was less than 0.2 Pa at 50 sccm total flow rate, the (1 1 1) peak of copper nitride appears. Thermal decomposition temperature of Cu₃N thin films deposited in pure nitrogen and 30 sccm flow rate was less than 300 °C. The surface morphology was smooth.     

Effect of deposition pressure on microstructure and properties of hydrogenated carbon nitride films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CN:H films) were deposited on n-type (1 0 0) silicon substrates making use of dual direct current radio frequency plasma enhanced chemical vapor deposition (DC-RF-PECVD), at working pressure of 2–20 Pa, using a mixed gas of CH₄ and N₂ as the source gas. The growth rate, composition, bonding structure of the deposited films were characterized by means of XPS and FTIR, and the mechanical properties of the deposited films were investigated by nano-indentation test. It was found that the parameters for the DC-RF-PECVD process had significant effects on the growth rate, structure and properties of the deposited films. The growth rate of the deposited films increased at first with increasing deposition pressure, then saturated with further increase of the deposition pressure. The N/C ratio inside the deposited films increased with increasing working pressure except that it was as much as 0.50 at a working pressure of 5.0 Pa. The nano-hardness of the films decreased with increasing deposition pressure. CN radicals were remarkably formed in the deposited films at higher pressures, and their contents are related to the nitrogen concentrations in the deposited films.     

Correlation between the method of preparation and the properties of the sol–gel HfO2 thin films

This work describes the preparation of HfO₂ thin films by the sol–gel method, starting with different precursors such as hafnium ethoxide, hafnium 2,4-pentadionate and hafnium chloride. From the solution prepared as mentioned above, thin films on silicon wafer substrates have been realized by ‘dip-coating’ with a pulling out speed of 5 cm min^?1. The films densification was achieved by thermal treatment for 10 min at 100 °C and 30 min at 450 °C or 600 °C, with a heating rate of 1 °C min^?1. The structural and optical properties of the films are determined employing spectroellipsometric (SE) measurements in the visible range (0.4–0.7 μm), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The main objective of this paper was to establish a correlation between the method of preparation (precursor, annealing temperature) and the properties of the obtained films. The samples prepared from pentadionate and ethoxide precursors are homogenous and uniform in thickness. The samples prepared starting from chloride precursor are thicker and proved to be less uniform in thickness. Higher non-uniformity develops in multi-deposition films or in crystallized films. A nano-porosity is present in the quasi-amorphous films as well in the crystallized one. For the samples deposited on silicon wafer, the thermal treatment induced the formation of a SiO₂ layer at the coating–substrate interface.     

Diffusion barrier properties of amorphous ZrCN films for copper metallization

A novel amorphous zirconium carbon nitrides (ZrCN) material was deposited by reactive sputtering using a ZrC target (99.5% in purity) in a mixture of Ar and N₂ ambient. The microstructure and mechanical properties of the ZrCN films were examined with respect to N₂ pressure. For thermal stability characterization, the stacked structure of Cu/ZrCN/Si was subsequently subject to thermal treatments at temperatures from 300 °C to 900 °C for 30 min in a vacuum tube with the base pressure of 3 × 10⁻⁵ torr. The results show that the amorphous ZrCN films exhibit superior mechanical properties to either ZrN or ZrC including hardness and elastic modulus. The stacked samples were shown to be thermally stable up to about 800 °C from Auger electron spectroscopy and X-ray diffraction, where the ZrCN still remains its amorphous phase. The device completely fails at 900 °C and the mechanism is discussed in the paper.     

Influence of oxygen partial pressure on the properties of undoped InOx films deposited at room temperature by rf-PERTE

Transparent and conductive/semiconductive undoped indium oxide (InO_x) thin films were deposited at room temperature. The deposition technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied between 3 × 10^?2 and 1.3 × 10^?1 Pa. Undoped InO_x films, 100 nm thick, deposited at the oxygen partial pressure of 6 × 10^?2 Pa show a conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about 1100 (Ω cm)^?1. For oxygen pressures greater than 6 × 10^?2 Pa, semiconductive films are obtained, maintaining the visible transmittance. Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 × 10^?2 Pa show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.     

Plasma enhanced chemical vapor deposition of ZnO thin films

Zinc oxide thin films were deposited on silicon and corning-7059 glass substrates by plasma enhanced chemical vapor deposition at different substrate temperatures ranging from 36 to 400 °C and with different gas flow rates. Diethylzinc as the source precursor, H₂O as oxidizer and argon as carrier gas were used for the preparation of ZnO films. Structural and optical properties of these films were investigated using X-ray diffraction, reflection high energy electron diffraction, atomic force microscopy and photoluminescence. Highly oriented films with (0 0 2) preferred planes were obtained on silicon kept at 300 °C with 50 ml/min flow rate of diethylzinc without any post annealing. Reflection high energy electron diffraction pattern also showed the crystalline nature of these films. A textured surface with rms roughness ∼28 nm was observed by atomic force microscopy for the films deposited at 300 °C. A sharp peak at 380 nm in the PL spectra indicated the UV band-edge emission.     

Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Structural study of undoped and (Mn, In)-doped SnO2 thin films grown by RF sputtering

Undoped and 5%(Mn, In)-doped SnO₂ thin films were deposited on Si(1 0 0) and Al₂O₃ (R-cut) by RF magnetron sputtering at different deposition power, sputtering gas mixture and substrate temperature. X-ray reflectivity was used to determine the films thickness (10–130 nm) and roughness (～1 nm). The combination of X-ray diffraction and Mössbauer techniques evidenced the presence of Sn⁴⁺ in an amorphous environment, for as-grown films obtained at low power and temperature, and the formation of crystalline SnO₂ for annealed films. As the deposition power, substrate temperature or O₂ proportion are increased, SnO₂ nanocrystals are formed. Epitaxial SnO₂ films are obtained on Al₂O₃ at 550 °C. The amorphous films are quite uniform but a more columnar growth is detected for increasing deposition power. No secondary phases or segregation of dopants were detected.     

Structural and optical properties of TiO2 thin films derived by sol–gel dip coating process

Nanocrystalline thin films of titanium dioxide have been fabricated on glass and silica substrates from partially hydrolyzed precursor solution. These films were subjected to heat treatment for 1 h at temperatures 100, 200, 300, 400, 500, 600, 700, 800 and 900 °C and characterized by XRD, SEM, XPS and optical techniques. As deposited films are found to be amorphous and also contain hydroxyl and organic functional groups. Films heat treated above 100 °C do not contain hydroxyl and organic functional groups. Microcrystalline behavior is observed in the films heat treated above 300 °C. Crystallite size increases from ∼5 to 50 nm as sintering temperature is increased from 300 to 700 °C. Formation of anatase phase with c-axis length 7.03 Å is observed in the films annealed up to 700 °C. These films peel off from the substrate beyond 700 °C annealing temperature. Density as well as refractive index of the films increases with increase in annealing temperature up to 700 °C. Refractive index is found to show Cauchys behavior. Transmission better than 70% is observed in the visible range. There is a strong absorption around 370 nm, which is attributed to band gap absorption of the material.     

Incipient amorphous-to-crystalline transition in HfO2 as a function of thickness scaling and anneal temperature

A series of 1.4, 1.8, and 4.0 nm thick HfO₂ films deposited on Si(1 0 0) substrates have been measured by extended X-ray absorption fine-structure prior to anneal processing, following a standard post deposition anneal of 700 °C for 60 s in NH₃ ambient, and following an additional rapid thermal anneal cycle of 1000 °C for 10 s in N₂ ambient. Analysis of the second coordination shell gives clear evidence of increased ordering with increasing film thickness at each temperature. Similarly, increased ordering with increasing anneal temperature is evident for each film thickness. Although X-ray diffraction and high resolution transmission electron microscopy indicated the 1.4 nm HfO₂ samples to be amorphous, EXAFS has distinguished nanocrystalline from amorphous states for these films.     

Growth and characterization of zirconium oxide thin films on silicon substrate

The growth and characterization of zirconium oxide (ZrO₂) thin films prepared by thermal oxidation of a deposited Zr metal layer on SiO₂/Si were investigated. Uniform ZrO₂ thin film with smooth surface morphology was obtained. The thermal ZrO₂ films showed a polycrystalline structure. The dielectric constant of the ZrO₂ film has been shown to be 23, and the equivalent oxide thickness (EOT) of the ZrO₂ stacked oxide is in the range of 3.38–5.43 nm. MOS capacitors with ZrO₂ dielectric stack show extremely low leakage current density, less than 10^?6 A/cm² at ?4 V. Consequently, using this method, high-quality ZrO₂ films could be fabricated at oxidation temperature as low as 600 °C.     

Optical characterization of sputtered amorphous aluminum nitride thin films by spectroscopic ellipsometry

We have measured and analyzed the optical constants and polarized optical properties of amorphous aluminum nitride (a-AlN) thin films deposited by RF reactive magnetron sputtering onto silicon(1 1 1) and glass substrates. The optical constants were obtained by analysis of the measured ellipsometric spectra in the wavelength range 300–1400 nm, using the Cauchy–Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range 1.80–2.11 and 8.6 × 10⁻³–1.5 × 10⁻⁵, respectively. Analysis of the absorption coefficient, in the wavelength range 200–1400 nm, shows the bandgap of a-AlN thin films to be 5.84 ± 0.05 eV. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 61° and a principal angle of 64°. Measurement of the polarized optical properties reveals a high transmissivity and very low absorptivity for a-AlN films in the visible and near infrared regions. X-ray diffraction analysis confirmed the amorphous nature of the films under study.     

Role of oxygen in structural properties of annealed CuAlO2 films

CuAlO₂ films were sputtered on quartz substrates at different oxygen partial pressures (OPP) and carried out the annealing at 900 °C for 5 h in N₂ ambient. The structural properties of these films have been studied in detail by X-ray diffraction, Raman spectroscopy, and atomic force microscopy. Annealed CuAlO₂ films are grown along the (0 0 1) preferential orientation. The film deposited at 20% OPP demonstrates the excellent crystalline behavior and the smallest electrical resistivity (41.8 Ω cm). At higher OPP, the crystalline behavior begins to degenerate up to the amorphous state at 60% OPP, and some micro-caves presented in the film surface become larger and deeper with the increase in OPP. We believe that the negative thermal expansion behavior associated with excess oxygen atoms is the primary responsibility for the change in structural properties.     

Te-rich Ge–As–Se–Te bulk glasses and films for future IR-integrated optics

Ge₁₅As₁₅Se_70−xTe_x materials with x = 56, 60 and 63, of potential use in IR-integrated optics, were prepared by the classical melt-quenching method. A macroscopic phase separation was observed with a crystalline phase on the top and an amorphous one at the bottom. The glasses from the bottom were transparent from 1.9 to 16 μm without any purification of the elemental precursors Ge, As, Te and Se. The higher the Te/Se content in the glasses the lower their glass transition temperature and thermal stability. Films 7–12 μm thick of the above stated compositions were deposited by thermal evaporation. The higher the tellurium content, the larger the optical band gap shift of the films in the infra-red and the higher the refractive index.     

MOCVD and characterization of Hf-silicate thin films using HTB and TEMAS

Hafnium silicate (HfSi_xO_y) films were deposited by metal-organic chemical vapor deposition (MOCVD) using a combination of precursors: hafnium tetra-tert-butoxide [Hf(OC(CH₃)₃)₄, HTB] and tetrakis-ethylmethylamino silane [Si(N(C₂H₅)(CH₃))₄, TEMAS]. The activation energy was independent on the ratio of precursor amounts in the surface reaction regime. The grown films showed Hf-rich characteristics and the impurity concentrations were less than 1 at.% (below detection limits). Hafnium silicate films were amorphous up to 700 °C annealing. Hf/(Hf + Si) composition ratio and dielectric constant (k) of the Hf-silicate films decreased by increasing the growth temperature above 270 °C.     

Evaluation of structural and mechanical properties of aluminum oxide thin films deposited by a sol–gel process: Comparison of microwave to conventional anneal

Thin films of Al₂O₃ have been deposited on polished silica glass substrates at room temperature by sol–gel dip coating technique followed by two different exposure methods. One set was annealed at different temperatures ranging from 200 °C to 800 °C for 10 h and a second set was exposed to microwave (2.45 MHz) radiation at different powers for 10 min. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwaves on solid phase diffusion. Unlike other preparation methods, microwave heating is generally quite faster, and energy efficient. X-ray diffraction (XRD) and scanning electron microscopy (SEM), energy dispersive X-ray analysis techniques have been employed to characterize structural, morphological and elemental compositions of the films. Adhesion strength failure measurements on films performed by scratch test in progressive loading sequence have shown critical loads up to 25 N (partial perforation) for both annealed films and films exposed to microwave irradiation. Nanohardness indentation tests of the films exposed (800 W) to microwave have shown hardness of 8.3 GPa with elastic modulus of 120 GPa compared to the conventional annealed film (800°) of 4.5 GPa with elastic modulus of 90 GPa.     

Low-temperature metal-induced crystallization of Mn-containing amorphous Ge thin films

This work focuses on the crystallization of amorphous germanium (a-Ge) thin films induced by manganese species. A series of Mn-containing a-Ge films ([Mn] ~ 0?3.7 at.% range) was deposited at 150 °C by the cosputtering technique. After deposition, all films were submitted to isochronal thermal annealing treatments up to 600 °C and analyzed by Raman scattering, optical transmission spectroscopy and electrical resistivity measurements. The experimental results indicate that: (a) Mn impurity lowers the crystallization temperature of a-Ge in ~ 100 °C, as confirmed by the Raman analyses, (b) the optical properties of the films are affected by both the insertion of Mn and the temperature of thermal treatment, with the optical bandgap staying in the range of ~ 0.7?1 eV, and (c) the electrical resistivity of the samples is also influenced by the Mn concentration and by the temperature of annealing, varying between ~ 1.0×10¹ and 1.6×10⁴ Ω cm. These experimental observations were systematically studied and the possible reasons associated to them are presented and discussed.     

GeO2 based high k dielectric material synthesized by sol–gel process

Recently, there has been lot of research on new high dielectric constant (high k) materials for use in future generations of ultra-large scale integrated circuits (ULSI). There are number of requirements for the new high k materials, such as high dielectric constant, thermal stability (400 °C or higher), high mechanical strength, and good adhesion to neighboring layers. Keeping in view the properties required for the replacement of existing SiO₂ dielectrics, new high k dielectric material based on GeO₂ has been synthesized. Polycrystalline GeO₂ thin films have been deposited by simple, and cost effective sol–gel spin coating process. The obtained xerogel films of germanium oxide have been annealed at 400 °C, 600 °C and 800 °C for 3 h in argon atmosphere. Elemental composition, morphology, and phase analysis have been measured by employing X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction techniques, respectively. The formation of the hexagonal GeO₂ phase at and above 400 °C has been reported. The composition of the annealed films have been measured and found to be 68 at.% of O, 32 at.% of Ge for GeO₂, which are close to the stoichiometry of the GeO₂.