Ti Alloy Films Research Articles

Impact of Ti Content on Cu–TaN Interfacial Properties, Cu Resistivity, and Ti Diffusion in Cu ∕ Cu ( Ti ) ∕ TaN ∕ Ta

We investigated the properties of the interface between Cu and TaN, Cu resistivity, and Ti diffusion in systems with Cu ( Ti) alloy films as the seed layer of electrochemical deposited (ECD) Cu film. The Cu(Ti) alloy films’ interfaces to the underlayer were improved compared with the Cu film interface. The use of Cu(Ti) films as a seed layer in the structure led to excellent thermal stability of Cu filling. The Cu(Ti) seed layers with Ti content above prevented voids from forming in Cu in a trench even after annealing at for , whereas a Cu seed layer caused voids. The Cu(Ti) layer affected not only the interfacial properties but also the resistivity of the ECD Cu film. The resistivity of ECD Cu films with Cu(Ti) alloys depended on the annealing temperature and Ti content. The resistivities of ECD Cu with Cu ( Ti) increased with annealing temperature. However, the ECD Cu with less than Ti had low resistivity even after annealing. The resistivity increase in each sample after annealing corresponded to the amount of Ti diffused from Cu(Ti) alloys to ECD Cu. These results clearly indicate that Cu(Ti) seed layers with less than Ti are potentially good for advanced Cu interconnects where both superior interfacial stability and low resistivity are required.

Effects of Substrate Materials on Self-Formation of Ti-Rich Interface Layers in Cu(Ti) Alloy Films

In our previous studies, thin Ti-rich layers were found to uniformly cover SiO2/Si substrate surfaces at the interface with Cu(Ti) alloy films after annealing at elevated temperature. These Ti-rich layers were also found to prevent intermixing between the Cu(Ti) alloy films and the substrate, resulting in a simple barrier formation technique, called “self-formation of the diffusion barrier,” which is attractive for fabrication of ultra-large scale integrated (ULSI) interconnect structures. In the present study, to understand the mechanism of self-formation of the Ti-rich barrier layers on the substrate surface, the effects of SiO2/Si, SiN/SiO2/Si and NaCl substrate materials on the interfacial microstructure were investigated. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) interconnects. It was concluded that the chemical reaction of Ti with the substrate materials was essential for the self-formation of the Ti-rich layers.

Self-Formation of Ti-rich Interfacial Layers in Cu(Ti) Alloy Films

To study the self-formation mechanism of Ti-rich layers in Cu(Ti) alloy films, the microstructures and electrical resistivities of the Cu(Ti) alloy films were investigated by changing the annealing atmosphere and substrate materials. Oxygen contained in Ar facilitated Ti segregation at the surface, reduced the Ti content in the alloy films, and formed relatively large grains in the alloy films, which are essential for low-resistivity Cu alloy films. For the self-formation of the Ti-rich barrier layer, it was found that the selection of a substrate that is reactive to Ti atoms (forming Ti compounds) was essential. Although a strong reaction of the Ti atoms in the alloy films with SiN compared with that with SiO2 was expected, the resistivities in the annealed Cu(Ti) alloy films on the SiN/Si substrates were higher than those on the SiO2/Si substrates. Further reduction of the resistivities is required for application of the fabrication process to devices.

The influence of substrate bias in I-PVD process on the properties of Ti and Al alloy films

The effects of substrate bias power on the microstructure, physical and electrical properties of thin Ti films prepared by ionized physical vapor deposition (I-PVD) process were studied. The influence of Ti underlayer with substrate bias power ranging from 0 to 400 W on the subsequent TiN/AlCu films deposited by conventional PVD process in a multilayer structure was further investigated. Decreasing substrate bias power led: (1) better Ti(002) texture, smoother surface, and lower resistivity in Ti films, and (2) better Al(111) texture, narrower grain size distribution, smoother final surface, better-defined TiN/AlCu interface, and lower residual stress in AlCu alloy films in the corresponding Ti/TiN/AlCu stacks. In both cases, lower substrate bias power resulted in films with desirable microstructures and properties, compared to higher bias powers, for use as Al-based interconnects in IC manufacturing.

Formation of Ti diffusion barrier layers in Thin Cu(Ti) alloy films

In order to study a formation mechanism of thin Ti-rich layers formed on the surfaces of Cu(Ti) wires after annealing at elevated temperatures, the 300-nm-thick Cu(Ti) alloy films with Ti concentration of 1.3 at.% or 2.9 at.% were prepared on the SiO2/Si substrates by a co-sputter deposition technique. The electrical resistivity and microstructural analysis of these alloy films were carried out before and after annealing at 400°C. The Ti-rich layers with thickness of ∼15 nm were observed to form uniformly both at the film surface and the substrate interfaces in the Cu(2.9at.%Ti) films after annealing (which we call the self-formation of the layers) using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Both the resistivities and the microstructures of these Cu(Ti) films were found to depend strongly on the Ti concentrations. The resistivities of the films decreased upon annealing due to segregation of the supersaturated Ti solutes in the alloy films to both the top and bottom of the films. These Ti layers had excellent thermal stability and would be applicable to the self-formed diffusion barrier in Cu interconnects of highly integrated devices. The selection rules of the alloy elements for the barrier self-formation were proposed based on the present results.

Conversion electron Mössbauer spectroscopy on random Fe–Ti alloy films prepared by pulsed laser deposition

Samples of thin films of α- 57Fe 1− x Ti x , 0 < x < 0.19, were prepared on Al 2O 3 single-crystalline substrate by pulsed laser deposition (PLD) at room temperature and investigated with Rutherford backscattering and conversion electron Mössbauer spectroscopy (CEMS). The Mössbauer spectra were analysed with an alloy model, assuming a purely random distribution of Ti atoms in α-Fe. The derived changes in hyperfine parameters as a function of the number of Ti atoms in the first two neighbour shells allow then to determine the effects of Ti on the Fe charge and spin densities. These results are compared to previous investigations of samples prepared by arc melting. We find distinct differences that may be related to the low solubility of Ti in α-Fe. The comparison demonstrates the usefulness of pulsed laser deposition for the preparation of random substitutional impurities distributions.

Correlation between growth stress and microstructure in CoCrPt alloy thin film with nanogranular structure

We have investigated in situ stress evolution for (Co82Cr18)87Pt13 /Ti alloy film in an ultrahigh vacuum (UHV) chamber equipped with a highly sensitive optical deflection-detecting system. A very large compressive stress is developed at the very beginning of CoCrPt alloy deposition, and it turns into a smaller tensile stress at about 5-Å CoCrPt thickness. After 20-Å CoCrPt deposition, the tensile stress again turns back to compressive stress. The microstructural studies at the each transition thickness region revealed that microstructural changes play a major role for the observed stress variation at the initial growth stage.

Microstructures of Nb–Ti alloy films prepared by ion beam assisted deposition

In Nb–Ti binary metal system with small size difference, metastable phases are prepared using ion beam assisted deposition. A Ti-rich fcc phase (fcc-I), a Nb-rich fcc phase (fcc-II) and a bcc phase are formed. The lattice constant of the fcc-I is 4.28 Å and is similar to that of the fcc-II phase. Evident texture is found in the Nb 30Ti 70 sample prepared using ion beam assisted deposition (IBAD) with ion energy of 2 keV. The texture mechanisms are analysed. Crystalline structure, atomic size, alloy effect, ion beam energy and kinetic model are used to analyse the formation process of the metastable phases and texture structure.

Low leakage current Cu(Ti)/SiO2 interconnection scheme with a self-formed TiOx diffusion barrier

Electrical and material properties of Cu(0.02 wt % Ti) alloy and pure Cu films deposited on SiO2/Si are explored. Current–voltage measurement using metal–oxide–semiconductor (MOS) capacitor structure reveals low leakage current (10−8 A/cm2) for capacitors with as-deposited Cu(0.02 wt % Ti) and pure Cu metal gates. However, after annealing at 700 °C in a vacuum, leakage current of MOS capacitors using a pure Cu gate shows a dramatic rise of leakage current at a low electrical field, while the leakage current of capacitors with Cu(0.02 wt % Ti) gate stays at ∼10−7 A/cm2. Concurrently, the resistivity of annealed Cu(0.02 wt % Ti) is reduced to 2.5 μΩ cm, which is only slightly greater than the resistivity of as-sputtered pure Cu films. X-ray photoelectron spectroscopy indicates that a TiOx layer has formed at the Cu(0.02 wt % Ti)/SiO2 interface after annealing and Auger electron spectrometry depth profiles show less interdiffusion at the Cu(0.02 wt % Ti)/SiO2 interface than the Cu/SiO2 interface. The correlation between leakage current reliability and the interfacial reaction upon annealing is discussed.

Electron transport properties of -phase Co Ti alloy films with various degrees of long range order

The influence of the structural disorder on the electron transport properties of Co0.50Ti0.50 alloy films in a temperature range of 4.2-300 K has been investigated at zero and 0.5 T of magnetic field. The disordered state in the alloy films was obtained by vapor quenching deposition onto substrates cooled by liquid nitrogen. The changes in the transport properties of the alloy films caused by the order-disorder structural transformation and the external magnetic field are explained by the analyses using various models for the electron transport in the disordered systems.

Nitrogen distribution and microstructure of hot implanted FeTi alloy films

The nitrogen distribution and microstructure of Fe and Fe-3 ∼ 65 at% Ti alloy films implanted with 2.5 × 10 21 ∼ 2 × 10 21 N 2 +/m 2 at the temperatures of 200°C, 350°C and 500°C were investigated. The nitrogen atoms implanted at 300°C or higher showed remarkable diffusion, shifting to the surface side in the Fe films, and redistributing over a wide region with relatively uniform concentration in the FeTi alloy films. Titanium nitride was observed in addition to iron nitride in the FeTi alloy films implanted with nitrogen at 350°C, and it was clearly observed that TiN with the size of 10 ∼ 50 nm diameter homogeneously dispersed in the specimens implanted at 500°C. The surface hardness of FeTi alloy films implanted with N 2 + ions increased with increases in the dose. A larger increase in the surface hardness was achieved at 350°C and 500°C implantation than at 200°C.

Formation of high temperature phases in sputter deposited Ti-based films below 100 °C

This article reports on the sputtering of pure Ti and Ti-based alloy films onto substrates where the temperature Ts was kept below 100 °C, using the magnetron sputter ion plating process. It was found that while the pure Ti film is a hexagonal low-temperature phase film (h–αTi), the Ti–Cr, and Ti–Fe alloy films, containing a relatively small amount of Cr or Fe of about 10 wt %, are cubic high-temperature beta phase Ti alloy films [c-βTi(Cr) or c-βTi(Fe)]. This finding is of immense importance both scientifically and practically. The conditions under which high-temperature phases are formed in alloy films sputtered at substrate temperatures below 100 °C, which is much lower than the temperature necessary to form these high-temperature phases (Thtp) according to the equilibrium phase diagram, will be discussed in detail. X-ray diffraction analyses of these films will also be presented.

Encapsulation of Ag films on SiO2 by Ti reactions using Ag–Ti alloy/bilayer structures and an NH3 ambient

Thin encapsulated silver films have been prepared on oxidized silicon by nitridation of ∼200-nm-thick Ag–19 at. % Ti alloy films and Ag(120 nm)/Ti(22 nm) at 300–700 °C in an ammonia ambient. The encapsulation process has been studied in detail by Rutherford backscattering, and scanning Auger and secondary-ion-mass spectrometry, which showed that Ti-nitride and Ti-oxide-silicide formation take place at the surface and the Ag–Ti/SiO2 interface, respectively. Four-point-probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼4 μΩ cm were measured in encapsulated Ag alloy films with initial low Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as-deposited Ag (∼3 μΩ cm).

Evolution of the microstructure of Cu(Ti)/SiO2 layers annealed in NH3

Copper-based metallization has recently attracted extensive research because of its potential application in ultra-large-scale integration (ULSI) of semiconductor devices. The feasibility of copper metallization is, however, limited due to its thermal stability issues. In order to utilize copper in metallization systems diffusion barriers such as titanium nitride and other refractory materials, have been employed to enhance the thermal stability of copper. Titanium nitride layers can be formed by annealing Cu(Ti) alloy film evaporated on thermally grown SiO2 substrates in an ammonia ambient. We report here the microstructural evolution of Cu(Ti)/SiO2 layers during annealing in NH3 flowing ambient.The Cu(Ti) films used in this experiment were prepared by electron beam evaporation onto thermally grown SiO2 substrates. The nominal composition of the Cu(Ti) alloy was Cu73Ti27. Thermal treatments were conducted in NH3 flowing ambient for 30 minutes at temperatures ranging from 450°C to 650°C. Cross-section TEM specimens were prepared by the standard procedure.

Enhanced Adhesion of Copper Films to SiO2, PSG and BPSG by Refractory Metal Additions

ABSTRACTCopper films generally exhibit poor adhesion on dielectrics. It has been shown that the addition of refractory metals promotes adhesion via an interfacial reaction or better wetting to the dielectric. We investigate the adhesion of Cu-refractory metal (Cr, Ti) alloy films and bilayers on various silicon oxide substrates (SiO2, PSG, BPSG) after annealing in the temperature range 400-600°C by conventional furnace using N2/H2 forming gas. Rutherford backscattering spectrometry (RBS) was used to determine the interfacial reaction characteristics. The efficacy of a variation of the standard Scotch™ tape testing was evaluated. We found that the combined Scotch™ tape/scribe adhesion test revealed excellent qualitative bonding information and could be correlated well to RBS characterization. We were able to optimize the sample configurations and chemical compositions to achieve the best adhering film.

Formation of TiN-encapsulated copper structures in a NH3 ambient

A TiN-encapsulated copper structure was made by annealing a Cu-10 at. %Ti alloy film evaporated on a SiO2/Si(100) substrate at 550 °C in a NH3 ambient. A fast heating rate (70 °C/min) to 550 °C can effectively suppress the formation of Cu3Ti and enhance the TiNx formation near the surface of the copper film. Oxygen incorporation in the TiNx layer was found by Auger depth profiling measurement. This self-encapsulated Cu structure exhibits good adhesion to SiO2 and oxidation resistance.

The Formation of TiN-Encapsulated Cu Interconnects

ABSTRACTA TiN(0)-encapsulated copper structure was made by annealing a Cu-10 at%Ti alloy film evaporated on a SiO2/Si(100) substrate in N2 or NH3 ambiente. During thermal cycling, the tensile stress in the nitridated films is in the range of 200 to 800 MPa. The stress relaxation depends on the cooling cycle and the presence of interlayer between film and substrate. A fast heating rate (70°C/min.) to 550°C in an NH3 ambient can effectively suppress the formation of Cu3Ti and enhance the TiNχ(0) formation near the surface of the copper film. This self-encapsulated Cu structure exhibits good adhesion to SiO2 and oxidation resistance. A fully encapsulated Cu fine line structure can be achieved by annealing a Cu-10at%Ti alloy film in an Ar ambient at 550°C and then in an NH3 ambient at 550°C to form TiOχ/Ti5Si3 adhesion layer and TiN(O) layer, respectively.

Electrical transport and i n s i t u x-ray studies of the formation of TiSi2 thin films on Si

The formation of TiSi2 thin films on Si has been investigated by in situ x-ray diffraction and electrical transport. The x-ray results show unequivocally that the staging proceeds through two orthorhombic polytypes of TiSi2 according to the sequence: sputter-deposited metallic Ti or TiSix alloy films on Si(001)→TiSi2 (C49 structure)→TiSi2 (C54 structure), with no evidence of lower silicides. Electrical transport shows metallic behavior for all phases and distinctive features in the annealing curves which correlate with the structural transformations. Most important, the resistivity, characteristically very high for the C49 phase, undergoes a precipitous drop at the C49→C54 transition. In the C54 phase when fully annealed the resistivity is 12.4 μΩ cm at room temperature and 0.66 μΩ cm at 4.2 K.

The hydrogen electrode reaction characteristics of thin film electrodes of Ni-based hydrogen storage alloys

Film-type electrodes of hydrogen absorbing intermetallic compound and alloys, LaNi 5, Ni 0.11 Ti 0.89, Ni 0.50 Ti 0.50 and Ni 0.76 Ti 0.24 were prepared by a flash evaporation method. The hydrogen electrode reaction characteristics of the LaNi 5 and NiTi alloy films in 1 M NaOH are very similar to each other. The reaction proceeds via the Volmer-Tafel reaction route with mixed rate-determining characteristics. The exchange current densities of the constituent steps, as well as the overall reaction, are in the range of 10 −6 A cm −2 (true). Surface analysis by an XPS technique has shown that La or Ti on the electrode surface exists as an electrocatalytically innert oxide of La 2O 3 or TiO 2. Close similarities of these electrodes with pure Ni electrodes indicate that Ni is responsible for the electrocatalytic activity. No synergistic effect is thus noticeable.

Magnetic and structural properties of Rh substituted Co-Cr alloy films with perpendicular magnetic anisotropy

RF sputtered Co0.78−xCr0.22Rhx (where x is 0–0.06) alloy films for high density perpendicular recording were studied. First, Co-M (M = Cr, Ti, V, Mo, Pd, and Rh) alloy films were studied. They exhibit hcp crystallization and have a high orientation of the c-axis normal to the film plane. However, they have a smaller coercive force (less than 300 Oe), and with the exception of Co-Cr, they do not have a columnar structure or satisfy the relation Hk ≳4πMs. Next, Co-Cr-Rh alloy films were studied. They also exhibit hcp crystallization and their structure is columnar. They show perpendicular magnetic anisotropy similar to that of Co-Cr, and in particular, a higher c-axis orientation was obtained. The ΔΘ50, half the width of a rocking curve of a (002) peak, is about 20–40% smaller than that of Co-Cr. By measuring the recording characteristics of Co-Cr-Rh disks (on an anodized aluminum substrate), a maximum recording density of 23,000FRPI was obtained.