Diffusion barrier performance of amorphous W-Ti-N films in Cu metallization

W-Ti-N films were prepared on a Si wafer by reactive sputter-deposition, followed by a deposition of a Cu thin film by DC magnetron sputtering. The Cu/W-Ti-N/Si samples prepared were annealed at different temperatures under vacuum and then characterized using X-ray diffraction, scanning electron microscopy and auger electron microscopy. The sheet resistivity was determined by four point probe analysis. The results show that the amorphous W-Ti-N film is mainly composed of TiN and W and the crystallization temperature is above 800 °C. W-Ti-N thin films prepared have good thermal stability at 700 °C, but the Cu film tends to agglomerate when the temperature is above 700 °C. A failure mechanism of the diffusion barrier is proposed based on the thermal stress and interface reaction.     

Corrosion behaviour of amorphous Ni–Si thin films on AISI 304L stainless steel

Abstract

Nanoscale Ni – Si thin films are widely used in commercial microelectronic devices because of their promising electrical properties as well as their chemical stability. However, their application in corrosive environment has not been frequently addressed in the literature. In this study, amorphous Ni_0.66Si_0.33, Ni_0.40Si_0.60, and Ni_0.20Si_0.80 thin films are prepared on AISI 304L stainless steel by means of ion-beam sputter (IBS) deposition and their corrosion behaviour is studied using potentiodynamic polarisation measurements. The electrochemical measurements were conducted in 0.05M HCl solution at room temperature. By means of optical interferometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the surface morphology and chemical composition of the thin films were examined before and after the electrochemical measurement. The evaluated results showed that the Ni–Si thin films may exhibit improved corrosion resistance over the 304L substrate provided that Si content is high enough to facilitate the formation of a Si-rich passive film.     

Electronic structure of amorphous InGaO3(ZnO)0.5 thin films

The electronic structure of amorphous semiconductor InGaO₃(ZnO)_0.5 thin films, which were deposited by radio-frequency magnetron sputtering process, was investigated using X-ray photoelectron spectroscopy and O K-edge X-ray absorption spectroscopy. The overall features of the valence and conduction bands were analyzed by comparing with the spectra of Ga₂O₃, In₂O₃, and ZnO films. The valence and conduction band edges are mainly composed of O 2p and In 5sp states, respectively. The bandgap of the films determined by spectroscopic ellipsometry was approximately 3.2 eV. Further, it is found that the introduction of oxygen gas during the sputter-deposition does not induce significant variations in the chemical states and band structure.     

Titanium nitride diffusion barrier for copper metallization on gallium arsenide

The diffusion properties of Cu, Cu/titanium nitride (TiN) and Cu/TiN/Ti metallization on GaAs, including as-deposited film and others annealed at 350-550 °C, were investigated and compared. Data obtained from X-ray diffractometry, resistivity measurements, scanning electron microscopy, energy dispersive spectrometer and Auger electron spectroscopy indicated that in the as-deposited Cu/GaAs structure, copper diffused into GaAs substrate, and a diffusion barrier was required to block the fast diffusion. For the Cu/TiN/GaAs structure, the columnar grain structure of TiN films provided paths for diffusion at higher temperatures above 450 °C. The Cu/TiN/Ti films on GaAs substrate were very stable up to 550 °C without any interfacial interaction. These results show that a TiN/Ti composite film forms a good diffusion barrier for copper metallization with GaAs.     

Phase formation, chemical composition and electrical studies of Ti/Si bilayer system

The annealing effects over a range of temperatures of the titanium film (90 nm) grown on Si(111) by electron gun evaporation technique were investigated using physical and electrical measurements. Grazing Incidence X-ray Diffraction experiment shows a stable titanium disilicides formation at higher annealing temperature. The depth profiling data using X-ray Photoelectron Spectroscopy show that the properties are closely related to the change of the interfacial layer and chemical state under the high-temperature annealing. The Schottky Barrier Height, as estimated by the current-voltage measurement is 0.75, 0.695, 0.662 and 0.60 eV for pristine and annealed samples at 450, 550 and 700 °C respectively.     

Influence of substrate doping on the surface chemistry and morphology of Copper Phthalocyanine ultra thin films on Si (111) substrates

16 nm thick Copper Phthalocyanine (CuPc) films were deposited at room temperature in Ultra High Vacuum onto “n” and “p” type doped Si(111) substrates covered with a native SiO₂ overlayer. Atomic Force Microscopy indicates that the two substrates are both atomically flat (0.15 nm root mean square roughness). Angle dependent X-ray photoemission spectroscopy shows that the thickness of the native SiO₂ over-layer is 0.8 nm (both for the “n” and “p” type Si substrate). Despite the identity of the substrate roughness, of the SiO₂ thickness, and of the CuPc film growth conditions, the organic films (made out of crystallites in the α-phase, as checked with X-ray Diffraction) grown on the “p” and “n” type substrate show clearly different morphological features (determined with Atomic Force Microscopy and Scanning Electron Microscopy measurements). While the CuPc film on “p” Si(111) shows a compact network of densely packed crystallites with sizes (along the substrate plane) ranging from 50 to 100 nm, the CuPc film on “n” Si(111) shows a slightly more open network of larger crystallites (with 75-150 nm size range). Accordingly, the CuPc film roughness is 0.67 nm and 1.15 nm for the “p” and “n” type substrate respectively. Due to the increased surface to volume effects (lower crystallite size) affecting the CuPc film on “p” Si(111), this film exhibits stronger interaction with oxygen and water vapor of the ambient air, as determined by photoemission spectroscopy experiments performed on samples as grown “in situ” and after prolonged (1 year) exposure to air.     

Diffusion barrier performance of nano-structured and amorphous Ru-Ge diffusion barriers for copper metallization

In the experiment, nano-structured and amorphous ultrathin Ru-Ge interlayers (∼15 nm in thickness) were deposited between Cu(Ru) alloy film and Si substrate via co-sputtering functioning as preventive diffusion barrier layers. After annealing at different temperatures, X-ray diffraction and four-point probe method revealed that the amorphous Ru-Ge layer effectively suppressed the Cu diffusion into Si substrate up to a temperature of at least 873 K; however, it is less than 773 K for the nano-structured Ru-Ge layer. A self-formed amorphous multilayer of Ru(RuO_x)/RuGe_xCu_y could be attained by annealing Cu/Cu(Ru)/Ru-Ge(amorphous)/Si system at a very low temperature (even 473 K). The results proved that the amorphous Ru-Ge system could self-form the multilayer diffusion barrier before the diffusion reaction between Cu and Si and improved the thermal stability of the Cu interconnection significantly.     

Thickness dependent electronic structure of ultra-thin tetrahedral amorphous carbon (ta-C) films

Microstructural properties of ultrathin (1-10 nm) tetrahedral amorphous carbon (ta-C) films are investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, X-ray Photoelectron Spectroscopy, Raman spectroscopy and Atomic Force Microscopy (AFM). The CK-edge NEXAFS spectra of 1 nm ta-C films provided evidence of surface defects (C―H bonds) which rapidly diminish with increasing film thickness. A critical thickness for stabilization of largely sp³ matrix structure distorted by sp² sites is observed via the change of π*C═C peak behavior. Meanwhile, an increase in the film thickness promotes an enhancement in sp³ content, the film roughness remains nearly constant as probed by spectroscopic techniques and AFM, respectively. The effect of thickness on local bonding states of ultrathin ta-C films proves to be the limiting factor for their potential use in magnetic and optical storage devices.     

Chemical states of carbon in amorphous boron carbide thin films deposited by radio frequency magnetron sputtering

Boron carbide thin films were deposited by radio frequency (RF) magnetron sputtering and characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high resolution transmission electron microscopy. The results reveal that the structure of thin films deposited at substrate temperatures lower than 350 °C is amorphous. We found that there are four chemical states for carbon in amorphous boron carbide thin films deposited by RF magnetron sputtering. One is the segregated carbon in form of the graphitic inclusions in the thin film identified by Raman spectroscopy and Raman mapping using two strong peaks at ~ 1360 cm^− 1 and ~ 1590 cm^− 1, but the XPS results show that the graphitic inclusions do not connect to the substrate directly. On the surface the carbon forms C=O bonds characterized by the peak of C1s core level at 285.0 eV besides B-C bonds in the boron carbide with the peak of C1s being at 282.8 eV. The detailed analysis of B-C bonds in the boron carbide shows that there are two states for carbon atoms in B-C bonds: in the C-B-C models with C1s peak at 282.3 eV and in the icosahedra with C1s peak at 283.3 eV.     

Surface and electrical studies of CuO:V2O5 thin films

Results from the studies of multicomponent CuO:V₂O₅ bulk material and thermally evaporated thin films of highly conducting bulk composition prepared at different substrate temperatures are thus compared and discussed. The electronic conductivity is enhanced on increase in the substrate temperature T_s and reaches a maximum value of 12.3 × 10⁻⁶Ω⁻¹ cm⁻¹ for T_s = 423 K. X-ray photoelectron spectroscopy studies indicate an increase in the reduced states of vanadium and copper ions in going from the bulk glass to the thin film. Dynamic secondary-ion mass spectroscopy studies on thin films over a depth of 3000 Å show a strong dependence of T_s on the Cu-to-V intensity ratio. Even though stoichiometric values for thin films are achievable by varying the T_s, the oxidation states of Cu in these films are predominantly monovalent. The electrical behaviors of these materials and their thin film counterparts are finally being discussed in relation to the surface analysis data.     

Epitaxial (Pb,La)(Zr,Ti)O3 thin films on buffered Si(100) by on-axis radio frequency magnetron sputtering

In this study, we discuss the case for integration of epitaxial (Pb,La)(Zr,Ti)O₃ (PLZT) thin films with silicon for electro-optic device applications. PLZT films, approximately 500 nm thick, were grown by on-axis radio frequency magnetron sputtering on CeO₂/YSZ-buffered Si(100) substrate with a SrRuO₃ electrode layer embedded between CeO₂ and PLZT. The structural properties and surface topography of the different oxide layers were examined with X-ray diffraction analysis and atomic force microscopy. The perovskite thin films were predominantly (001)-oriented, with a (002) rocking curve halfwidth of approximately 0.3° and a surface roughness compatible with requirements for application in optical devices. The PLZT cation stoichiometry was assessed from quantitative X-ray photoelectron spectroscopy. These measurements uncovered a substantial depletion of lead in the film surface for layers deposited at substrate temperatures above ~ 600 °C, whereas the surface concentration of La, Zr and Ti remained virtually unaffected over a wide range of growth temperatures.     

Changes in atomic and electronic structures of amorphous WO3 films due to electrochemical ion insertion

The structural changes in amorphous WO₃ films were investigated both on the atomic and electronic levels, and the experimental findings were interpreted using molecular orbital calculations. Electrochemical fast intercalation resulted in the splitting of a peak in the valence band region of the X-ray photoelectron spectrum. This splitting could be attributed to the formation of non-bridging oxygen. Decomposition of WO₆ units into WO₄ units could also be inferred from the data. This decomposition was, however, not responsible for the split of the photoelectron peak. From the population analyses it was found that the average bond strength decreased due to the intercalation, while select WO bonds increased in strength. It was expected that these changes in the chemical bonding character lead to localization of electrons and distortion of WO₆ units, which was consistent with the theoretical interpretations of electrochromism, the intervalence charge transfer model and the small polaron absorption theory.     

Diffusion barrier capability of Zr-Si films for copper metallization with different substrate bias voltage

Efficiency of Zr-Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr-Si diffusion barriers were deposited on the Si substrates by reactive magnetron sputtering with different negative substrate bias. The mass density of Zr-Si films increases with substrate bias voltage up to − 150 V. The deposition rate decreased with the negative substrate bias from 5.4 nm/min to 1.8 nm/min. XRD measurements show that the Zr-Si barriers have amorphous structure in the as-deposited state. The FE-SEM images show that the sizes of spherical granules on the Zr-Si film surface increase with increasing the substrate bias. The Cu/Zr-Si/Si structures were prepared and annealed in Ar ambient at temperatures varying from 500 to 650 °C for an hour. It is shown from the comparison study that the Zr-Si film deposited with − 150 V is better at maintaining good performance in Cu/Zr-Si/Si contact system than that of Zr-Si film deposited with − 50 V.     

Structural characterization of thin amorphous Si films

We present a study of structural changes occurring in thin amorphous silicon (a-Si). The a-Si films were deposited on single-crystalline Si substrates held at room temperature or 200 °C by magnetron sputtering of a Si target in pure Ar atmosphere, and therefore the films were hydrogen-free. All samples were annealed in vacuum and subsequently studied by EPR and GISAXS. A strong decrease in the dangling bonds content at lower annealing temperatures, and then an increase of it at around 550 °C, suggested significant structural changes. In parallel the samples were studied by GISAXS which confirmed changes at the nanometric scale attributed to voids in the material. A nice correlation of the results of the two techniques shows advantages of this approach in the analysis of structural changes in a-Si material.     

Structure and mechanical properties of low temperature magnetron sputtered nanocrystalline (nc-)Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings

This paper reports on the structure and mechanical properties of ~ 2 μm thick nanocomposite (nc-) Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings deposited on 100Cr6 steel substrates, using low temperature (~ 200 °C) DC reactive magnetron sputtering. The carbon content was varied with acetylene partial pressure in order to obtain single layer coatings with different a-C:H carbon phase fractions. The nanocrystalline Ti(N,C) phase is approximately stoichiometric for all coatings and the a-C:H phase fraction increases from 31 to 47 at.% as the coatings stoichiometry changed from TiC_1.34 N_0.51 to TiC_2.48 N_0.48, respectively. TiC_1.34 N_0.51 coatings showed the highest nanoindentation hardness (H) of ~ 14 GPa and a modulus (E_r) of ~ 144 GPa; H reduced to < 6 GPa and E_r to < 70 GPa for TiC_2.48 N_0.48 coatings. nc-Ti(N,C)/a-C:H coatings are promising candidates for applications where better matching of the modulus between a relatively low modulus substrate, hard loading support layer and low modulus-high H/E ratio top layer is required.     

Evaluation of diffusion barrier and electrical properties of tantalum oxynitride thin films for silver metallization

The thermal stability and the diffusion barrier properties of DC reactively sputtered tantalum oxynitride (Ta-O-N) thin films, between silver (Ag) and silicon (Si) p⁺n diodes were investigated. Both materials characterization (X-ray diffraction analysis, Rutherford backscattering spectrometry (RBS), Auger depth profiling) and electrical measurements (reverse-biased junction leakage current-density) were used to evaluate diffusion barrier properties of the thin films. The leakage current density of p⁺n diodes with the barrier (Ta-O-N) was approximately four orders of magnitude lower than those without barriers after a 30 min, 400 °C back contact anneal. The Ta-O-N barriers were stable up to 500 °C, 30 min anneals. However, this was not the case for the 600 °C anneal. RBS spectra and cross-sectional transmission electron microscopy of as-deposited and vacuum annealed samples of Ag/barrier (Ta-O-N)/Si indicate the absence of any interfacial interaction between the barrier and substrate (silicon). The failure of the Ta-O-N barriers has been attributed to thermally induced stresses, which cause the thin film to crack at elevated temperatures.     

XPS and X-ray diffraction studies of aluminum-doped zinc oxide transparent conducting films

Aluminum-doped zinc oxide transparent conducting films are prepared by spray pyrolysis at different dopant concentrations. These films are subsequently characterized by X-ray diffractometric and X-ray photoelectron spectroscopic (XPS) techniques. The results are compared with those obtained from pure zinc oxide films prepared under identical conditions. X-ray diffraction measurements show an increase in lattice parameters (c and a) for aluminum-doped films while their ratio remains the same. This study also indicates that within the XPS detection limit the films are chemically identical to pure zinc oxide. However, a difference in the core-electron line shape of the Zn 2p_3/2 photoelectron peaks is predicted. An asymmetry in Zn 2p_3/2 photoelectron peaks has been observed for aluminium-doped films. The asymmetry parameters evaluated from core-electron line-shape analysis yield a value of the order of 0.04±0.01. The value is found to lie between those obtained for pure zinc oxide and has been attributed to the presence of excess zinc in the films.     

Structural analysis of amorphous Si films prepared by magnetron sputtering

A study is presented on the structural changes occurring in thin amorphous silicon (a-Si) during thermal treatments. The a-Si films were deposited on single-crystalline Si substrates held at room temperature by magnetron sputtering of a Si target in pure Ar atmosphere, and therefore the films were hydrogen-free. All samples were annealed in vacuum and subsequently studied by electron paramagnetic resonance (EPR) and grazing incidence X-ray diffraction (GIXRD). A slight increase in the dangling bonds content at lower annealing temperatures, and then a strong increase of it at around 650 °C, suggested significant structural changes. The samples were also studied by grazing incidence small-angle X-ray scattering (GISAXS) which confirmed changes at the nanometric scale attributed to voids in the material. A nice correlation of the results of the three techniques shows advantages of this approach in the analysis of structural changes in a-Si material.     

Spectroscopic ellipsometry characterization of amorphous carbon and amorphous, graphitic and fullerene-like carbon nitride thin films

Carbon nitride (CN_x) and amorphous carbon (a-C) thin films are deposited by reactive magnetron sputtering onto silicon (001) wafers under controlled conditions to achieve amorphous, graphitic and fullerene-like microstructures. As-deposited films are analyzed by Spectroscopic Ellipsometry in the UV-VIS-NIR and IR spectral ranges in order to get further insight into the bonding structure of the material. Additional characterization is performed by High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Between eight and eleven resonances are observed and modeled in the ellipsometrically determined optical spectra of the films. The largest or the second largest resonance for all films is a feature associated with C-N or C-C modes. This feature is generally associated with sp³ C-N or sp³ C-C bonds, which for the nitrogen-containing films instead should be identified as a three-fold or two-fold sp² hybridization of N, either substituted in a graphite site or in a pyridine-like configuration, respectively. The π→π? electronic transition associated with sp² C bonds in carbon films and with sp² N bonds (as N bonded in pyridine-like manner) in CN_x films is also present, but not as strong. Another feature present in all CN_x films is a resonance associated with nitrile often observed in carbon nitrides. Additional resonances are identified and discussed and moreover, several new, unidentified resonances are observed in the ellipsometric spectra.     

Valence number transition and silicate formation of cerium oxide films on Si(100)

Interface reactions of a Ce-oxide layer with Si(100) wafers have been characterized by X-ray photoelectron spectroscopy. The ratio of Ce atoms in Ce³⁺ states within the Ce-oxide layer has been found to decrease from 47% at as-deposited sample to 26% after annealing. From detailed reaction analysis of valence number transitions of Ce atoms and the creation of SiO₂ layer at the interface, the reacted Ce³⁺ atoms are converted into silicates and Ce⁴⁺ with a ratio of 2:1. The energy bandgap of Ce-silicate layer has been determined as 7.67 eV and the valence band offset with respect to Si(100) wafer has been extracted as 4.35 eV.