Deposition Of Thin Metal Films Research Articles

Dual ion-beam deposition of metallic thin films

The influence of argon ion-beam bombardment of growing Al, Mo and Ti thin films deposited by ion-beam sputtering on their composition and optical properties was studied. The Ar ion energy and ion-to-atom arrival ratio were 100–600 eV and 0.15–1.75 respectively. The concentration of Mo (A1) in the thin films decreased (increased) with ion energy as the Ar content increased (decreased). The Ti content was below 35% for all ion energies. The ratio O/Ti was close to the stoichiometric value of two for all ion energies up to 400 eV. Higher ion-beam energies and doses led to higher values of the index of refraction for Al and Ti thin films. Furthermore, an increase in the energy of the ions caused a decrease in the deposition rates of all films due to resputtering of the thin film atoms and, in the case of Al thin films, intensified the amorphization process in the Al/Si structure.

Surface force-induced bonding at metal multiasperity contacts

Adhesion at multiasperity contacts of clean metal surfaces obtained by rupture in an ultrahigh vacuum and by vacuum deposition of thin metal films onto flat surfaces has been investigated. Indium and lead were chosen in this study because their high surface energy to hardness ratios allowed us to expect a marked surface force effect in adhesion. In the region of small applied loads, the adhesion coefficient varied from ~1 to ~200 while surface roughness Ra varied from ~120 to ~0.01 μm. In the case of smooth surfaces (Ra = 0.01-0.03 μm), complete bonding of the contacting surfaces at room temperature and under small applied loads (0.1-0.5 MPa, which is much smaller than the yield stress of metals in contact) occurred. This effect is considered to be evidence of a surface force contribution to adhesion. Such effect appeared to be useful in bonding non-metallic materials by the use of thin metal films as an adhesion-promoting interlayer.

Computational and Experimental Studies Of Grain Growth

ABSTRACTThis paper addresses the validity of the single particle growth law rn-r0n=Kt in describing the formation of 3D grains during the vapor deposition of thin metal films, especially with respect to the value of the exponent n. Computer simulations based on the Huygen’s construction showed that the grain size distribution at full surface coverage did not depend significantly on the specific model chosen for initiating growth from nuclei. The particle size distributions obtained experimentally by STM measurements of thin Au films deposited on glass substrates agreed very well with the simulation results for n=2.

Temperature dependence of atomic mixing at the copper-silicon interface

The atomic mixing and formation of silicides during deposition of a thin film onto a substrate are caused by diffusion processes which are dominated by thermal effects and are also influenced by the energy of the incident particles. Sputter deposition of metal thin films on a silicon substrate shows the formation of silicides at the interface of metal and silicon. This is particularly marked in the case of copper thin films deposited onto silicon. In this paper, the influence of the substrate temperature on broadening of the mixed layer at the interface is discussed and experimental results are presented. The mixing profiles and the compositions of the silicides near the interface are evaluated using Rutherford backscattering spectroscopy. The experimental results show that sputter deposition at a temperature below 550 K causes moderate interfacial mixing (the silicide thickness is about a few tens of nanometers) while at comparatively higher temperatures the intermixed layers are broadened to more than 200 nm.

On the efficiency of deposited energy density for ion beam mixing processes with ions implanted during and after thin metal film deposition

The influence of the energy density deposited in collision cascades (DED) on the efficiency of the intermixing processes across bilayer interfaces was studied. The systems under investigation were bilayers of Cu on Al (Cu/Al), Pd/Fe, Cr/Ti, Cu/Ti, W/Ti. The bilayer structures were irradiated with 6–30 keV Ar +, Kr +, Cr +, Cu +, W + ions at doses up to 8×10 16 cm −2. The value of DED varied from 0.2 to 13 eV/at. The mixing profiles were obtained by using the RBS technique. The changes of relative concentrations of the intermixed components show that for some systems the rate of interface mixing increases parallel with DED.

Laser ablation deposition and magnetic characterization of metallic thin films based on rare earth and transition metals

Laser ablation deposition (LAD) is a very promising technique for the preparation of thin films and multilayers. Technical difficulties inherent in the method have been solved. In particular a velocity selector has been developed leading to almost complete elimination of the droplets ejected from the target. The magnetic properties of a series of model systems prepared by LAD have been studied. The anisotropy of 30ÅFe(110)/W(110)/Al 2O 3(112¯0) is discussed. Epitaxial bilayers of 5ÅGd(0001)/25ÅFe(110)/W(110) have been obtained; the Gd moments are antiparallel to the Fe moments. Thin films of Y 2Co 17(0001) have been successfully grown on W(110)/Al 2O 3(112¯0) and their magnetic properties have been characterized.

Model for beam-induced deposition of thin metallic films

Recent advances in focused ion beam (FIB) technology have expanded the applications of beam-induced deposition (BID) of thin metallic films in microcircuit fabrication. This paper provides a model for the BID process by examining the effects on film growth and morphology of various deposition parameters including the incident ion flux, adsorbate coverage of the substrate and residue, residue sputtering, and energy deposition by incident ions. Residue nucleation is examined, and a significant difference between adsorbate coverage of the substrate and residue is found to introduce large thickness variations in the film. Adsorbate depletion which is caused by an increase in the ion beam current density or target temperature results in a larger energy deposition per residue molecule and is proposed as a mechanism for enhancement of the metallic purity and electrical conductivity of the residue. By investigating the film growth rate during periodic ion bombardment characteristic of focused ion beams, the model demonstrates that the maximum film growth rate is obtained by maximizing the scanning frequency. The model is found to quantitatively agree with published experimental results.

Metal/semiconductor interfacial reactions

Vapor phase deposition of thin metal films on semiconductors followed by annealing frequently leads to the nucleation and growth of one or more reaction products in the vicinity of the metal/ semiconductor interface. Often, these products are intermetallic compounds that may be distributed as precipitates in the interfacial region. The composition, size, shape, and areal density of these precipitates may be the major factors in determining the electrical properties of the interface. The semiconductors studied were GaAs, SiC, and semiconducting diamond, while the metals were principally the refractory metals, although several other metals were also investigated. The interfaces of representative samples were examined using Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), including selected area electron diffraction (SAD), and optical metallography. The electrical properties were evaluated by current-potential (I-V) and Hall effect measurements.

Shear Strength and Tribological Properties of Stearic Acid Films—Part II: On Gold-Coated Glass

This paper reports measurements of the shear strength of dry and lubricated Au/Au, Al/Au and glass/Au couples from measurements of the frictional force during sliding of a hemispherical pin in contact with a flat side. The Au and Al surfaces are generated by vacuum deposition of thin metal films on glass. Shear strength is measured at a sliding speed of 60 μm s−1 and at contact stresses ranging from ~ 0.05 to 0.8 GPa. Lubrication is achieved by depositing a stearic acid on the slide. The shear strength of dry glass/Au sliding interfaces is found to increase linearly with contact stress but decreases slightly with increasing thickness of the gold film. The shear strength of dry Au/Au interfaces is larger than that of dry glass/Au. Stearic acid does not protect gold from mechanical wear during sliding because the acid is expelled from the gold/gold interface, even at the lowest compressive stresses used. These observations are interpreted in terms of the weak adhesion of stearic acid to gold. In contrast, stearic acid sustains mechanical shear in interfaces consisting of gold sliding on either bare glass or aluminum, to which the acid adheres. These observations suggest that a boundary lubricant film protects against mechanical wear if it adheres only to one of the contacting surfaces.

Thin metal film characterization and chemical sensors: monitoring electronic conductivity, mass loading and mechanical properties with surface acoustic wave devices

Acoustoelectric coupling between charge carriers in a thin metal film and the evanescent electric field associated with a surface acoustic wave (SAW) propagating along the surface of a piezoelectric substrate provides a unique interaction mechanism with which to study the film's electronic charfe transport properties, as well as changes in these properties resulting from chemisorption from the gas phase. We utilized 97 MHz ST-cut quartz- and 32 MHz Y-cut LiNbO 3-based SAW devices to follow (1) the process of vacuum deposition of thin metal films (5–500 Å), (2) the (room temperature) relaxation of such films after their deposition, and (3) the chemisorption-induced changes in both the mass density and electrical conductivity of such films. Changes in mass density were followed with a resolution exceeding 1% of a monolayer. Sheet conductivity measurements made with the 97 MHz SAW device correlated well with simultaneous measurements made with a d.c. electrometer. In addition, changes in the mechanical properties of freshly deposited thin films were observed during relaxation and when gaseous species interact with them; we believe this is a result of adsorption predominantly along grain boundaries. The combination of responses to three different physical parameters can be utilized in the design of chemical sensors.

Low pressure magnetron sputtering using ionized, sputtered species

Abstract The possibility of a self-sustained magnetron sputtering process, without the presence of an inert gas, is demonstrated. The advantages of this process are as follows: the possibility of thin metal film deposition at very low pressures p ⩽ 4 × 10−4 Torr; a very high sputtering rate; an absence of inert gas particles in the deposited films; a possibility of deposition on substrates placed at a distance from the target much smaller than the mean free path; a decrease in the plasma discharge influence on substrate, the substrate can be placed at a greater than usual distance from the target. Low pressure magnetron sputtering using target ions opens new possibilities for thin film deposition. The method combines the advantages of both electron beam evaporation (purity, rate) and sputtering (good adhesion, repeatability, free choice of deposition geometry).

Characterization of metal-overlayer growth-modes in Auger crystal surface analysis

A general procedure for Auger-analysis characterization of the modes of growth during deposition of metal thin films onto layer-structured crystalline substrates is presented. It takes into account the crystallographic electron attenuation in both the overlayer structures and in the substrate layers, and it is found that the maximum Auger electronic escape-depth has a minimum at monolayer coverage. The model, which is based on ratios between electronic attenuation lengths, or between electronic inelastic mean free paths, is tested on thin-film growth of yttrium on MgO(100) and of yttrium and copper, respectively, on LaAlO 3(100); its predictions on the modes of growth are confirmed, and it is further indicated that the degree of charge distribution and the change in bond lengths in the interface region may decrease with yttrium coverage.

In-Situ Optical Emission Spectra of Ti, TiN and TiSi2 Plasma During Thin Film Growth by Pulsed Laser Evaporation

AbstractThe first optical emission spectra of Ti, TiN and TiSi2 plasma during growth of thin films by pulsed laser evaporation has been reported. A KrF excimer laser (248nm) with pulsewidth of 45ns operating on 5Hz repitition rate was used for deposition of refractory metal thin films using varying laser fluence of 4J/cm2 to 15J/cm2. Most of the radiative species seen in plasma belongs to atomic neutrals and ionic species such as Ti I, Ti II, Si I, Si II and N 11. Emission spectra was mostly dominated by neutral and ionic emission from Titanium (Ti I and Ti II).

Thin Film Synthesis Using Miniature Pulsed Metal Vapor Vacuum arc Plasma Guns

Metallic coatings can be fabricated using the intense plasma generated by the metal vapor vacuum arc. We have made and tested an embodiment of vacuum arc plasma source that operates in a pulsed mode, thereby acquiring precise control over the plasma flux and so also over the deposition rate, and that is in the form of a miniature plasma gun, thereby allowing deposition of metallic thin films to be carried out in confined spaces and also allowing a number of such guns to be clustered together.The plasma is created at the cathode spots on the metallic cathode surface, and is highly ionized and of directed energy a few tens of electron volts. Adhesion of the film to the substrate is thus good. Virtually all of the solid metals of the Periodic Table can be used, including highly refractory metals like tantalum and tungsten. Films, including multilayer thin films, can be fabricated of thickness from Angstroms to microns. We have carried out preliminary experiments using several different versions of miniature, pulsed, metal vapor vacuum arc plasma guns to fabricate metallic thin films and multilayers.Here we describe the plasma guns and their operation in this application, and present examples of some of the thin film structures we have fabricated, including yttrium and platinum films of thicknesses from a few hundred Angstroms up to 1 micron and an yttrium-cobalt multilayer structure of layer thickness about 100 Angstroms.

Chemical vapor deposition of CoGa and PtGa2 thin films from mixed-metalorganometallic compounds

A new process for deposition of thin metal films from organometallic precursors of limited volatility has been demonstrated. Short path vapor transport of the complexes dichloro(tetracarbonylcobalt)gallium(III) tetrahydrofuranate, (CO)4CoGaCl2(THF), or platinum(bis-dimethylglyoximato)(bis-dimethylgallium), Pt{(N2C2(CH3)2O2)(GaMe2)}2, each under a stream of hydrogen, leads to the films of the intermetallic compounds CoGa and PtGa2, respectively, on substrates such as Si (100) wafer or a glass slide at 500 °C. The compounds were identified and characterized by x-ray diffraction, Auger electron and x-ray photoelectron spectroscopies. The films are crystalline and highly reflective. The CoGa film is single phased; the PtGa2 film shows a minor constituent of Pt2Ga3.

Modeling studies of rare earth-transition metal optical recording media in relation to experiment

Ballistic aggregation models were utilized to explore and explain the possible origins of thickness, compositional and magnetic variations encountered in the sputter deposition of rare earth-transition metal thin films. They were also used to examine the influence of sputter gas pressure on details of microstructural evolution including columnar growth, defect propagation and surface roughness. The simulations, in agreement with experimental observations, pointed to the advantages of low pressure (<10 mTorr) deposition conditions which resulted in dense, featureless films and minimized the adverse effects of substrate irregularies and defects. The observed increase in corrosion resistance of these films was attributed to this densification.

Reactions at the interface of metal/HgCdTe oxide

The interfacial reactions between metals and the anodic oxide of mercury cadmium telluride (MCT) have been studied by polar-angle-dependent x-ray photoelectron spectroscopy. It was found that the deposition of thin metal films (&amp;lt;2 nm) of indium, platinum, and gold reduced the oxidized tellurium of the MCT oxide at the interface. The spectral results show that indium is more reactive than platinum and gold, but the latter two metals still cause similar interfacial interactions. In the study of the reaction mechanism, depositions of indium and gold by direct evaporation ruled out the possibility that the observed interfacial reactions are caused by energetic particles arriving at the surface during sputter deposition. Metal deposition on MCT oxide which was separated from the MCT substrate also ruled out the possibility of metal diffusion through pinholes in the oxide. It is possible that the condensation of metal causes the breaking of tellurium–oxygen bonds and thereby initializes the interfacial reactions.

Pulsed laser ablative deposition of thin metal films

Abstract Different mechanisms of pulsed laser ablation and ablative deposition of thin metal films at various fluences are discussed. The window for clear ablation, i.e. the fluence range in which the film is completely removed without any damage of the supporting substrate and the window for best quality printing are determined.

Selective area deposition of metal thin films on ceramic substrates by laser-induced plating.

This paper describes the feasibility of selective area deposition of metal thin films onto ceramic substrates by using a laser-induced plating technique. In experiments, a focused YAG laser beam and a copper electroless plating solution including CuSO4 were used. For the ceramic workpieces, aluminum nitride (AlN) substrate without activation was used. As a result, a copper deposit was produced on the ceramic surface only in regions where the laser beam was irradiated. A very high plating rate of about 2 μm/s was achieved. This plating enhancement rate is about 1×103 times the usual plating rate. The specific resistance of the copper film was about 3×10-8 Ωm. As an application, the direct drawing of copper lines was demonstrated with a writing speed of 0.2 mm/s.

Laser Ablation Deposition (LAD) of Metallic Thin Films

ABSTRACTSeveral experiments have been carried out to characterize the laser ablation deposition of metallic thin films as a function of the various process parameters. Ablation thresholds have been investigated for Al, Cu and Au targets as a function of wavelength as well as the fluence dependence of ablation rate. The effect of electric fields on the particle component of the ablated material has been investigated. Measurements of the velocity distribution of these particles have also been carried out for Al, Cu and Au targets as a function of the laser parameters with a view to using a velocity filter to remove the particles from the ablated beam.