Deposition Of Thin Metal Films Research Articles

Highly sensitive measurements of the energy transferred during plasma sputter deposition of metals

This work reports results obtained from heat flux measurements performed during the deposition of metallic thin films by low-pressure plasma sputtering. It introduces a sensitive diagnostic, which allows us to perform such measurements directly during the process and to follow in real-time mechanisms involved in the plasma/surface interaction. Although quantitative results are provided and discussed, the main scope of this paper is a qualitative study of the sputter-deposition process via the energy flux transfers. The diagnostic developed for energy flux measurements is presented and the versatility of the experimental apparatus is described. Results on the study of the deposition of Pt (and Fe) thin films demonstrate a good reproducibility of the measurements and the ability to separate the energetic contribution of the main plasma (∼300 mW cm−2) from the deposition process contribution (2 to 23 mW cm−2). The influence of gas pressure, plasma power and target bias voltage on the energy transferred to the silicon substrate is also studied.

Low‐Temperature Atomic Layer Deposition of Copper Metal Thin Films: Self‐Limiting Surface Reaction of Copper Dimethylamino‐2‐propoxide with Diethylzinc

A uniform, conformal, pure copper metal thin film was grown at very low substrate temperatures (100-120 degrees C) on Si(100) substrates by atomic layer deposition involving the ligand exchange of [Cu(OCHMeCH(2)NMe(2))(2)] with Et(2)Zn (see scheme). Patterned copper thin films of Cu nanotubes (diameter 150 nm, length 12 microm) were fabricated.

Low‐Temperature Atomic Layer Deposition of Copper Metal Thin Films: Self‐Limiting Surface Reaction of Copper Dimethylamino‐2‐propoxide with Diethylzinc

AbstractEin einheitlicher, winkeltreuer dünner Film aus reinem Kupfermetall wurde bei sehr niedrigen Substrattemperaturen (100–120 °C) auf Si(100)‐Substraten durch Atomlagenabscheidung erzeugt, an der ein Ligandenaustausch beteiligt ist (siehe Schema). Gemusterte dünne Kupferfilme aus Cu‐Nanoröhren (Durchmesser 150 nm, Länge 12 μm) wurden ebenfalls hergestellt.magnified image

Nanohole 3D-size tailoring through polystyrene bead combustion during thin film deposition

A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H 2O and CO 2 generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4–24 nm and diameter of 10–36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO 2 or Al 2O 3. These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters.

Atomic Layer Deposition of Platinum Oxide and Metallic Platinum Thin Films from Pt(acac)2 and Ozone

Platinum oxide and platinum thin films have been grown by atomic layer deposition (ALD) using Pt(acac)2 (acac = acetylacetonato) and ozone as precursors. Amorphous platinum oxide thin films were deposited at 120 and 130 °C while metallic platinum films were obtained at 140 °C and above. The sublimation temperature of Pt(acac)2 set the low temperature limit for oxide film deposition. The platinum oxide films were successfully deposited on Al2O3 and TiO2 adhesion layers, soda lime glass, and silicon substrate with native oxide on top. Platinum films were grown on Al2O3 adhesion layer. The platinum oxide had good adhesion to all tested surfaces, whereas metallic platinum films did not pass the common tape test. Resistivities of 50−60 nm thick platinum oxide films were between 1.5 and 5 Ω cm at 130 °C and could be varied with both precursor pulse lengths. The resistivity of about 110 nm thick metallic film deposited at 140 °C was about 11 μΩ cm. The platinum films deposited at higher temperatures suffered from deterioration of thickness uniformity. The platinum oxide films can be reduced in 5% H2 gas under reduced pressure at room temperature to porous platinum structures.

The application of ITTFA and ARXPS to study the ion beam mixing of metal/Si bilayers

AbstractMetal/silicon interfaces produced by metal thin film deposition on Si substrates have been ion beam mixed using either Ar+ or reactive N2+ low‐energy ion beams. The ion beam mixing (IBM) has been studied by means of ultraviolet photoelectron spectroscopy (UPS), X‐ray photoelectron spectroscopy (XPS), angle resolved XPS (ARXPS) and iterative target testing transformation factor analysis (ITTFA). The IBM using Ar+ is characterized by the formation of metal silicide. For the IBM interfaces using N2+, a fast nitrogen incorporation in the near surface region, followed by a steady state, is observed. Once the saturation is reached, the Me/Si ratio can be varied in a broad range with a nearly constant nitrogen concentration, as a consequence of sputtering, nitruration and mixing effects taking place simultaneously. The comparison of the experimental results with those obtained from TRIDYN simulations that uses pure ballistic mechanisms, suggests that additional rate‐controlling mechanisms, as radiation‐enhanced diffusion processes or the chemical reaction with nitrogen, have to be considered to explain the IBM of Me/Si interfaces by low‐energy Ar+ and N2+ bombardment. Copyright © 2008 John Wiley & Sons, Ltd.

Fabrication of Complex Metallic Nanostructures by Nanoskiving

This paper describes the use of nanoskiving to fabricate complex metallic nanostructures by sectioning polymer slabs containing small, embedded metal structures. This method begins with the deposition of thin metallic films on an epoxy substrate by e-beam evaporation or sputtering. After embedding the thin metallic film in an epoxy matrix, sectioning (in a plane perpendicular or parallel to the metal film) with an ultramicrotome generates sections (which can be as thin as 50 nm) of epoxy containing metallic nanostructures. The cross-sectional dimensions of the metal wires embedded in the resulting thin epoxy sections are controlled by the thickness of the evaporated metal film (which can be as small as 20 nm) and the thickness of the sections cut by the ultramicrotome; this work uses a standard 45 degrees diamond knife and routinely generates slabs 50 nm thick. The embedded nanostructures can be transferred to, and positioned on, planar or curved substrates by manipulating the thin polymer film. Removal of the epoxy matrix by etching with an oxygen plasma generates free-standing metallic nanostructures. Nanoskiving can fabricate complex nanostructures that are difficult or impossible to achieve by other methods of nanofabrication. These include multilayer structures, structures on curved surfaces, structures that span gaps, structures in less familiar materials, structures with high aspect ratios, and large-area structures comprising two-dimensional periodic arrays. This paper illustrates one class of application of these nanostructures: frequency-selective surfaces at mid-IR wavelengths.

Filtered vacuum arc deposition of undoped and doped ZnO thin films: Electrical, optical, and structural properties

Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50–400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO 2, In 2O 3:Sn (ITO), ZnO:Al (AZO), ZnO:Ga, ZnO:Sb, ZnO:Mg and several types of zinc-stannate oxides (ZnSnO 3, Zn 2SnO 4), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post-deposition treatment has also been applied to improve the properties of TCO films. The deposition rate of FVAD ZnO and ZnO:M thin films, where M is a doping or alloying metal, is in the range of 0.2–15 nm/s. The films are generally nonstoichiometric, polycrystalline n-type semiconductors. In most cases, ZnO films have a wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as-deposited n-type thin ZnO film is in the range 0.2–6 × 10 − 5 Ω m, carrier electron density is 10 23–2 × 10 26 m − 3 , and electron mobility is in the range 10–40 cm 2/V s, depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ∼ 3.3 eV and its extinction coefficient ( k) in the visible and near-IR range is smaller than 0.02, the optical transmission of 500 nm thick ZnO film is ∼ 0.90.

PIEZOELECTRICALLY DRIVEN MICROTRANSDUCER MASS SENSORS

ABSTRACT Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr0.52,Ti0.48)O3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼300 μm) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When various microtransducers are compared, the microcantilever exhibited the highest gravimetric sensitivity factor (Δf/Δm×f0 = 694.4 cm2/g), followed by the microbridge and microdiaphragm. However, the microbridge showed the highest mass sensitivity (Δf/Δm = 137.5 Hz/ng) among those transducers.

Stress evolution during intermittent deposition of metallic thin films

Copper, silver and gold thin films were deposited on Si(0 0 1) substrates at room temperature in UHV vacuum system. The process was intermittent in a periodic way i.e. for each sublayer the deposition was interrupted for about 10 min. The total force per unit width ( F/ w) was in situ determined in deposited films by the use of the substrate curvature measurement method with laser scanning technique. Significant stress evolution during the interruption periods was observed for Cu and Ag layers whereas no evolution was observed for Au layers. Differences in the growth character are discussed basing on the Volmer–Weber growth model.

Polymer MEMS processing for multi-user applications

We have developed a new polymer MEMS process that shows enormous flexibility in design parameters. This process uses entirely spin-on layers for structural and sacrificial materials. Further, this process flow is designed for multiple users to fabricate as many devices as possible on the same wafer which up to this point has not been demonstrated with polymer MEMS technologies. In this process, all structural layers are fabricated out of negative tone SU-8 photoresist and all sacrificial and separation layers are defined by a thin film of polystyrene. Using entirely spin-on layers for structural and sacrificial materials provides an easy way to select layer thicknesses without having to significantly alter the materials or processing techniques. A metal thin-film deposition step is also incorporated that allows electrical connection to the microstructures and actuators in this process. To characterize the robustness and flexibility of this technology we have fabricated a variety of in-plane and out-of-plane microstructures including chevron-type thermal actuators and tested their mechanical and electromechanical operation. The entire process sequence is accomplished at temperatures below 200 °C, making this technology compatible for post-processing integration of MEMS on an electronics circuit wafer.

Supercritical-carbon dioxide-assisted cyclic deposition of metal oxide and metal thin films

Thin films of aluminum oxide and palladium were deposited on silicon at low temperatures (70–120°C) by a cyclic adsorption/reaction processes using supercritical CO2 solvent. Precursors included Al(hfac)3, Al(acac)3, and Pd(hfac)2, and aqueous H2O2, tert-butyl peracetate, and H2 were used as the oxidants or reductants. For the precursors studied, growth proceeds through a multilayer precursor adsorption in each deposition cycle, and film thickness increased linearly with the number of growth cycles.

PIEZOELECTRICALLY DRIVEN MICROTRANSDUCER MASS SENSORS

ABSTRACT Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr0.52,Ti0.48)O3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼ 300 μ m) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When various microtransducers are compared, the microcantilever exhibited the highest gravimetric sensitivity factor (Δ f/Δ m < eqid1 > f 0 = 694.4 cm2/g), followed by the microbridge and microdiaphragm. However, the microbridge showed the highest mass sensitivity (Δ f/Δ m = 137.5 Hz/ng) among those transducers.

Vacuum Arc Plasma Guns and Ion Sources

Vacuum arc plasma can be formed using particularly uncomplicated hardware, providing a means for laboratory scale formation of dense and highly-ionized metal plasma. The simplicity and versatility of the approach has led to its widespread use in recent times for both fundamental and technological applications. When embodied in a plasma gun configuration, the source can provide a valuable tool for plasma deposition of metal and metal-containing thin films, including in plasma immersion configurations. When embodied in an ion source configuration, high current beams of metal ions can be formed, and such beams have found good use for ion implantation and particle accelerator injection. Here we briefly review vacuum arc plasma guns and ion sources, outlining some of the hardware embodiments that have been developed at Berkeley and used for various materials modification applications.

The application of atomic layer deposition for metallization of 65 nm and beyond

With the implementation of Cu interconnect technology, the conventional thin film deposition technique including physical vapor deposition (PVD) shows its fundamental limitation with 65 nm technology node and beyond and the need for introducing metal thin film deposition technique with excellent conformality and controllability of thickness at nanometer scale has been increased. For nanoscale devices, each of the layers or structures used in the interconnect features should be as thin and as perfect as possible. Atomic layer deposition (ALD) has sparked a lot of interest in the interconnect world for a number of reasons. The process is intrinsically atomic in nature, and results in the controlled deposition of films in sub-monolayer units. Ideally, film thickness is determined by number of deposition cycles, rather than timing of a continuous deposition process (like PVD) with a precalibrated deposition rate. Besides application as a diffusion barrier, metal films deposited by ALD is expected to be used in other critical interconnect area including direct platable layer and contact applications. In this presentation, we will present the development of ALD process for various metals and metal nitride layers including Ta, TaN, and Ru focusing on applications for back end of the line process.

Laser-induced surface activation of LTCC materials for chemical metallization

Low-temperature cofired ceramics (LTCCs) are mainly applied in hybrid microelectronics packaging technology, where the fabrication of metallic conductors on LTCC materials is done using various printing technologies. The conventional process is fast and cost-effective in the case of mass production, but too slow and difficult when repair and/or modifications of the circuitry are needed. Printing also fails when deposition of thin metal films on LTCC is required. Here, a simple laser-assisted process is presented, by which the surface of LTCCs can be activated for consecutive electroless chemical metal plating. The method enables the realization of thick high-conductance metallic Cu micropatterns and thin seed layers of Ag and Au, with a lateral resolution of a few tens of micrometers. The process is also suitable for 3-D-MEMS applications. A study of LTCC surfaces treated with Nd:YAG pulses is carried out using field emission scanning electron microscope (FESEM), SEM, x-ray diffraction (XRD) and Raman measurements.

Versatile Portable Device for Solid-State Electrical Measurements of “Soft” Materials

We describe a versatile portable prototype device for electrical measurements of “soft” materials. It consists of a custom-made micromanipulator and a gas-tight syringe to hold a mercury mini-drop to make reliable and controllable electrical contacts with solid-state materials of interest. Compared with the conventional method (deposition of thin metal films under vacuum), the proposed experimental approach is simpler and more cost-effective.

Fabrication of a nanoelectromechanical switch using a suspended carbon nanotube

Fabrication and characterization of a nanoelectromechanical switching device consisting of a suspended multiwalled carbon nanotube and self-aligned electrodes is reported. The device has a triode structure and is designed so that a suspended carbon nanotube is mechanically switched to one of two self-aligned electrodes by repulsive electrostatic forces between the nanotube and the other self-aligned electrode. Carbon nanotubes are dispersed on an SiO2 coated Si wafer and their locations recorded using a scanning electron microscope mapping process. Contact electrodes and self-aligned deflection electrodes are formed by a process comprising electron beam lithography, metallic thin film deposition, and lift-off. The electrical measurements show well-defined ON and OFF states with change of gate voltage. The measured threshold voltage for electromechanical switching is ∼3.6V.

Imaging of doped Si in low and very low voltage SEM: the contrast interpretation

Secondary electron (SE) imaging of planar doped n-type Si has been performed using low voltage (LV) and very low voltage scanning electron microscopy (VLVSEM). The effect of the surface contamination and the SE contrast mechanism has been investigated in two microscopes operated at two different vacuum conditions. SE imaging under conventional vacuum and ultra high vacuum (UHV) conditions with in situ cleaning of the sample surface enables one to identify the contribution of the surface adlayer on the SE contrast. Carrying out in situ thin metal film deposition experiments under UHV conditions validates the proposed contrast mechanism at very low voltages. Also it is reported that the SE contrast depends on the thickness of the surface layer as well as the electron beam voltage used for SE imaging.

Atomic layer deposition of metal and nitride thin films: Current research efforts and applications for semiconductor device processing

Atomic layer deposition (ALD) has been studied for several decades now, but the interest in ALD of metal and nitride thin films has increased only recently, driven by the need for highly conformal nanoscale thin films in modern semiconductor device manufacturing technology. ALD is a very promising deposition technique with the ability to produce thin films with excellent conformality and compositional control with atomic scale dimensions. However, the applications of metals and nitrides ALD in semiconductor device processes require a deeper understanding about the underlying deposition process as well as the physical and electrical properties of the deposited films. This article reviews the current research efforts in ALD for metal and nitride films as well as their applications in modern semiconductor device fabrication.