Effect of heating on the residual stresses in TiN films investigated using synchrotron radiation

The structure and residual stresses of TiN films deposited by arc ion plating (AIP) on a steel substrate were investigated using a synchrotron radiation system that emits ultra-intense X-rays. In a previous study, the crystal structures of TiN films deposited by AIP were found to be strongly influenced by the bias voltage. When high bias voltages were used, TiN films that were approximately 200 nm thickness had a preferred orientation of {110}, whereas TiN films that were approximately 600 nm thickness has a multilayer film orientation of {111}/{110}. In this present study, the two-tilt method was used to evaluate the residual stresses in TiN films by measuring lattice strains in two directions determined by the crystal orientation. Residual stresses in 600-nm-thick as-deposited TiN films were found to be −10.0 GPa and −8.0 GPa for {111}- and {110}-textured layers, respectively, while they were −8.0 GPa for {110}-textured layers in 200-nm-thick as-deposited TiN films. Residual stresses of both films relaxed to thermal stress levels upon annealing.     

Synthesis and characterization of carbon/silica superhydrophobic multi-layer films

C/SiO₂ multi-layer films (3-layer films and 5-layer films) were obtained by sol-gel method and physical deposition on glass plates, and then heated at 500 °C for 1 h under a nitrogen atmosphere. The mechanical adhesive force with the substrate of the multi-layer films was sharply enhanced compared to the as-deposited amorphous carbon film. An absorption layer was formed on heat treated C/SiO₂ multi-layer films by modification of the surface with trimethylchlorosilane, and the wettability of the films changed from hydrophilic to super-hydrophobic. The structures of the physically deposited carbon and the multi-layer films were analyzed by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The experimental results showed that the 5-layer films had a concentric ring structure that caused the film to be superhydrophobic.     

Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

Diffusion barrier property of TiN and TiN/Al/TiN films deposited with FMCVD for Cu interconnection in ULSI

Flow modulation chemical vapor deposition (FMCVD) with titanium tetrachloride (TiCl₄) and ammonia (NH₃) is effective for depositing titanium nitride (TiN) films with conformal morphology, good step coverage, low electrical resistivity, and low chlorine residual contamination. It means that FMCVD TiN film is a good candidate of diffusion barriers for copper interconnection technology in ULSI. But the diffusion barrier property of FMCVD TiN film against Cu diffusion has not been confirmed. So, firstly, we deposited Cu (100 nm)/FMCVD TiN (25 nm)/Si multilayer films and investigated the thermal stability of Cu/TiN/Si structure. Vacuum annealing was done at 400, 500, 550 and 600 °C. For films annealed for 30 min at 400 °C, Cu diffused through the TiN layer and formed copper silicides on the surface of Si substrates. Therefore, FMCVD films formed under such conditions are unsatisfactory diffusion barriers. To enhance the diffusion barrier property of FMCVD TiN films, we used sequential deposition to introduce a monolayer of Al atoms between two TiN films. Etch-pit tests showed that for TiN films with Al interlayer, Cu diffusion through the barrier occurred at 500 °C and that is 100 °C higher than TiN film without Al interlayer. Al atoms formed AlO_x with oxygen atoms present in the TiN films as impurities, and fill up the grain boundaries of TiN film, thereby blocking the diffusion of Cu atoms.     

Intrinsic stress effect on fracture toughness of plasma enhanced chemical vapor deposited SiNx:H films

The apparent fracture toughness for a series of plasma enhanced chemical vapor deposition SiN_x:H films with intrinsic film stress ranging from 300 MPa tensile to 1 GPa compressive was measured using nanoindentation. The nanoindentation results show the measured fracture toughness for these films can vary from as high as > 8 MPa⋅√m for films in compression to as low as < 0.5 MPa⋅√m for the films in tension. Other film properties such as density, Young's modulus, and hydrogen content were also measured and not observed to correlate as strongly with the measured fracture toughness values. Various theoretical corrections proposed to account for the presence of intrinsic or residual stresses in nanoindent fracture toughness measurements were evaluated and found to severely underestimate the impact of intrinsic stresses at thicknesses ≤ 3 μm. However, regression analysis indicated a simple linear correlation between the apparent fracture toughness and intrinsic film stress. Based on this linear trend, a stress free/intrinsic fracture toughness of 1.8 ± 0.7 MPa⋅√m was determined for the SiN_x:H films.     

Optimization of the structural, microstructural and optical properties of nanostructured Cr:ZnSe films deposited by magnetron co-sputtering for mid-infrared applications

In order to obtain optimally adherent films having the highest mid-infrared photoluminescence efficiency, nanostructured Cr²⁺:ZnSe films were deposited at room temperature on various substrates by magnetron radiofrequency co-sputtering of a SiO₂ target covered by a given number of ZnSe and Cr chips, at different Argon pressures and radiofrequency powers. The deposition parameter effect on the compositional, structural, microstructural and optical properties of the films has been investigated using X-ray reflectivity and diffraction, optical transmission spectroscopy, transmission electron microscopy, and photoluminescence studies. The corresponding films are composed by highly textured cubic and hexagonal ZnSe phases and exhibit strong tensile in-plane residual stresses. The evolution of the tensile residual stress and porosity values are consistent with the optical properties of the layers, and in particular the evolutions of both optical gap and refractive index. The room temperature mid-infrared (2-3 μm) photoluminescence measurements under direct excitation (1850 nm) revealed that chromium has been incorporated in the Cr²⁺ active state, and the corresponding fluorescence efficiency for an optimized thin film is only two times smaller than the one of a Cr²⁺:ZnSe reference bulk single crystal.     

Diffusion and adhesion properties of Cu films on polyimide substrates

Copper thin films were prepared on polyimide (PI) substrates by physical vapor deposition (PVD) and chemical vapor deposition (CVD). Titanium nitride (TiN) diffusion barrier layers were deposited between the copper films and the PI substrates by PVD. Auger electron spectroscopy compositional depth profile showed that TiN barrier layer was very effective in preventing copper diffusion into PI substrate even after the Cu/TiN/PI samples were annealed at 300 °C for 5 h. For the as-deposited CVD-Cu/PI, CVD-Cu/TiN/PI, and as-deposited PVD-Cu/PI samples, the residual stress in Cu films was very small. Relatively larger residual stress existed in Cu films for PVD-Cu/TiN/PI samples. For PVD-Cu/TiN/PI samples, annealing can increase the peeling strength to the level observed without a diffusion barrier. The adhesion improvement of Cu films by annealing treatment can be attributed to lowering of the residual tensile stress in Cu films.     

Preparation and thermoelectric properties of nc-Si:(Al2O3 + SiO2) composite film

A composite film of nanocrystalline Si (nc-Si) embedded in (Al₂O₃ + SiO₂) has been prepared on a quartz substrate by thermally evaporating a 400 nm thick Al film on a quartz substrate and annealing in air at 580 °C for 1 h. During annealing, the Al reacts with the SiO₂ of the quartz substrate and produces nc-Si, which is embedded in the (Al₂O₃ + SiO₂) film. The average size of nc-Si is ~ 22 nm and the thickness of the nc-Si:(Al₂O₃ + SiO₂) composite film is ~ 810 nm. It is found that the prepared film is thermoelectric with a Seebeck coefficient of − 624 μV/K at 293 K and − 225 μV/K at 413 K.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

Improvement of the (1 1 1) texture and microstructures of Cu films by pulsed laser annealing

The improvement of the (1 1 1) texture and microstructure of Cu films on TiN/Si and TiN/SiO₂ substrates by pulsed KrF laser annealing as a function of the laser energy density, the deposition method of Cu films, and the orientation of TiN substrates is studied. Upon annealing at an energy density below 1.0 J cm^–2 the (1 1 1) texture of the evaporated Cu films increases with the energy density, whereas for the sputtered Cu films the (2 0 0) texture is promoted. The higher oxygen concentration in the sputtered Cu films may be responsible for the degradation of the Cu(1 1 1) texture. The enhancement of the Cu(1 1 1) texture is more evident for (1 1 1)-oriented TiN substrates than for (2 0 0)-oriented TiN substrates. The present study shows that pulsed laser annealing is superior to vacuum annealing in improving the (1 1 1) texture and microstructure of Cu films via the melt/solidification process.     

CexAlyOz/TiN stack analysis for Metal-Insulator-Metal applications: Effect of annealing and the metal electrode deposition method

Ce_xAl_yO_z thin films were deposited on TiN metal electrode by metalorganic chemical vapour deposition method at 400 °C. The detailed physical characterization on Ce_xAl_yO_z/TiN stack upon annealing at different temperatures (600 °C and 850 °C) and for different deposition methods (Atomic vapour deposition (AVD) and Physical vapour deposition (PVD)) of electrode material were done for possible Metal-Insulator-Metal applications. X-ray diffraction results exhibited that the dielectric and TiN(AVD) are amorphous while TiN(PVD) is crystalline for the as deposited stacks. Annealing on Ce_xAl_yO_z/TiN(AVD) at 600 °C, initiates CeO₂ crystallization in the dielectric with composition of Ce:Al = 0.5 as obtained by X-ray photoelectron spectroscopy. In Ce_xAl_yO_z/TiN(PVD) stack, the dielectric remains in its amorphous state until 850 °C. However, TiO₂ crystallization is formed at 600 °C in Ce_xAl_yO_z/TiN(PVD). Time of flight secondary ion mass spectroscopy depth profiling data proves that the annealing at 600 °C caused the oxidation of both the metal electrodes and the inter-diffusion of Ti from the bottom metal electrode through the dielectric layer.     

Comparative study on the characteristics of network and continuous Ni films

Ni films were deposited on anodic aluminum oxide (AAO) and SiO₂/Si(100) substrates at 300 K by direct current magnetron sputtering with the oblique target. The film thickness was 80 nm, 160 nm and 260 nm. The films grown on AAO substrates have a network structure while those deposited on SiO₂/Si(100) substrates are continuous. The network film consists of granules and is formed by granule connection. The granule consists of many fine grains. The granule size increases with increasing film thickness. The 80 nm-thick network film has a honeycomb-like structure. The continuous films grow with a columnar structure and the transverse size of columnar grains increases with increasing film thickness. All the network films show a Ni(111) diffraction peak while the 160 nm- and 260 nm-thick continuous films exhibit the Ni(111) and Ni(200) diffraction peaks. The network films have higher coercivity and residual magnetization ratio compared with the continuous films. The coercivity and the residual magnetization ratio increase with increasing film thickness for the network films while they are almost independent of the film thickness for the continuous films. A temperature dependence of the resistance within 5-200 K reveals that the 80 nm-thick network Ni film exhibits markedly a minimal resistance at about 40 K. A logarithmic temperature dependence of the conductance is verified at temperatures below 40 K. The temperature coefficient of resistance is smallest for the 80 nm-thick network film and is largest for the 260 nm-thick continuous film.     

Effect of SiO2 passivation overlayers on hillock formation in Al thin films

Hillock formation in Al thin films with varying thicknesses of SiO₂ as a passivation layer was investigated during thermal cycling. Based on the stress measurements and the number of hillocks, 250 nm thick SiO₂ was thick enough to suppress the hillock formation and the suppression of hillock at 250 nm passivation and the lack of suppression at thinner passivation is related to the presence/absence of protection against the diffusive flow of atoms from the surrounding area to the surface due to the biaxial compressive stresses present in the film through the weak spots in the passivation layer. The stress state of Al films measured during annealing (the driving force for hillock formation) did not vary much with SiO₂ thickness. A small number of hillocks formed during the plasma enhanced chemical vapor deposition of SiO₂ overlayers at 300 °C.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

Large area Ba1 − xSrxTiO3 thin films for microwave applications deposited by pulsed laser ablation

Large area Ba_1 − xSr_xTiO₃ (BST) thin films with x = 0.4 or x = 0.5 were deposited on 75 mm diameter Si wafers in a pulsed laser deposition (PLD) chamber enabling full-wafer device fabrication using standard lithography. The deposition conditions were re-optimized for large PLD chambers to obtain uniform film thickness, grain size, crystal structure, orientation, and dielectric properties of BST films. X-ray diffraction and microstructural analyses on the BST films grown on Pt/Au/Ti electrodes deposited on SiO₂/Si wafers revealed films with (110) preferred orientation with a grain size < 100 nm. An area map of the thickness and crystal orientation of a BST film deposited on SiO₂/Si wafer also showed (110) preferred orientation with a film thickness variation < 6%. Large area BST films were found to have a high dielectric tunability of 76% at an electric field of 400 kV/cm and dielectric loss tangent below 0.03 at microwave frequencies up to 20 GHz and a commutation quality factor of ~ 4200.     

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.     

High dielectric tunability of Ba0.6Sr0.4TiO3 thin film deposited by radio-frequency magnetron sputtering

In microwave tunable devices, one of the major challenges encountered is the simultaneous minimization of the material's dielectric loss and maximization of dielectric tunability. In this work, Ba_0.6Sr_0.4TiO₃ thin film with the thickness of 300 nm was deposited on Pt/SiO₂/Si substrates using radio-frequency magnetron sputtering technique, and its dielectric properties were investigated. Due to the high temperature annealing process at substrate temperature of 600 °C, well-crystallized Ba_0.6Sr_0.4TiO₃ film was deposited. The dielectric constant and dielectric loss of the film at 100 kHz are 300 and 0.033, respectively. Due to the good crystallinity of the Ba_0.6Sr_0.4TiO₃ films deposited by radio-frequency magnetron sputtering, high dielectric tunability up to 38.3% is achieved at a low voltage of 4.5 V.     

Influence of Cu diffusion conditions on the switching of Cu-SiO2-based resistive memory devices

This paper presents a study of Cu diffusion at various temperatures in thin SiO₂ films and the influence of diffusion conditions on the switching of Programmable Metallization Cell (PMC) devices formed from such Cu-doped films. Film composition and diffusion products were analyzed using secondary ion mass spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction and Raman spectroscopy methods. We found a strong dependence of the diffused Cu concentration, which varied between 0.8 at.% and 10^− 3 at.%, on the annealing temperature. X-ray diffraction and Raman studies revealed that Cu does not react with the SiO₂ network and remains in elemental form after diffusion for the annealing conditions used. PMC resistive memory cells were fabricated with such Cu-diffused SiO₂ films and device performance, including the stability of the switching voltage, is discussed in the context of the material characteristics.     

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.     

Synthesis and luminescence characterization of manganese-activated willemite gel films

Manganese-activated willemite (α-Zn_2 − xMn_xSiO₄; x = 0.05-0.20) phosphor thin films with bright green light emission were deposited on silicon wafers by a sol-gel process. Zinc chloride, tetraethylorthosilicate, and manganese chloride were employed as precursors. The sol-gel transition, crystallization process and photoluminescence of processed films were investigated. The level of manganese doping did not greatly affect the crystallinity, but did affect the gelation rate and luminescence of films. X-ray diffraction and infrared spectrum studies revealed that single-phase willemite started to crystallize at around 600 °C. After thermal annealing at 600°-1200 °C, the crystallinity of films increased with increasing heating temperature and thickness of films. The emission intensity of the film was strongly related to the crystallinity and deposition conditions. Controlling the dopant content, number of coating layers and annealing temperature could significantly enhance the brightness of the green emission. The luminescence properties of α-Zn₂SiO₄:Mn films are characterized by fluorescence spectra and decay lifetime measurements.