Sputtered Metal Films Research Articles

Effect of magnetron sputtering process parameters on the conductivity of thin metal film

This paper focuses on the effect of magnetron sputtering process parameters on the performance of thin metal film. Copper–tin alloy metal film was deposited on both sides of the PVDF film using direct current magnetron sputtering technology, and the effects of different working pressures, sputtering powers, sputtering times, and argon flow rates on the uniformity, deposition rate, and electrical conductivity of the metal film were studied separately. The main and minor factors affecting the conductivity of the metal film were determined by multiple linear regression, and the process parameters were optimized. The optimal process parameters include a working pressure of 0.065 Pa, a sputtering power of 70 W, a sputtering time of 20 min, and an argon flow of 20 SCCM. The samples with the best electrical conductivity were analyzed by scanning electron microscopy and energy spectrometry for microscopic morphology and elemental composition. The experimental results showed that the sputtering time and sputtering power have a greater effect on the metal film uniformity and that the working pressure and argon flow rate have a smaller effect on the metal film uniformity; when the working pressure is lower, the sputtering power is higher, the sputtering time is longer, the argon flow rate is higher, and the conductivity of the sputtered metal film is better. The deposition rate decreased with the increase in the working pressure and increased with the increase in the sputtering power and argon flow rate. The working pressure is the main factor affecting the conductivity of the metal film, and the sputtering power and sputtering time are secondary factors.

Surface-enhanced Raman scattering used to study the structure of layers formed on metal surfaces from single-stranded DNA and 6-mercaptohexan-1-ol: influence of hybridization with the complementary DNA and influence of the metal substrate.

Capture single-stranded DNA with an attached alkanethiol linking moiety (capture HS-ssDNA) and 6-mercaptohexan-1-ol were chemisorbed on nanostructured GaN covered with sputtered layers of plasmonic metals (like silver and gold). The structure of the formed layer was determined by surface-enhanced Raman scattering (SERS) measurements. Hybridization with the target ssDNA, complementary to the chains of immobilized capture HS-ssDNA, induced changes in the conformation of the chains of chemisorbed ω-substituted alkanetiols (6-mercaptohexan-1-ol and the alkanethiol linking moiety of HS-ssDNA). Such changes are significantly larger in the case of experiments on silver than on gold and gold/silver SERS substrates. This means that silver substrates are significantly more promising for the SERS observation of such hybridization-induced rearrangements than the gold substrates previously used. Although the sputtered metal films have a nanograin structure, the nanostructuring of the GaN substrates plays an important role in the SERS-activity of this nanomaterial.

Homologous substrate-temperature dependence of structure and properties of TiO2, ZrO2, and HfO2 thin films deposited by reactive sputtering

Group 4 metal oxides TiO2, ZrO2, and HfO2 were deposited on glass substrates at substrate temperatures ranging from 100 to 800 °C by reactive direct current magnetron sputtering using an Ar and O2 mixture as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the homologous substrate-temperature dependence of the film structure and properties for the sputter-deposited metal oxide thin films are discussed. The x-ray diffraction measurements show the diffraction patterns characteristic of the anatase (tetragonal) structure at substrate temperatures below 400 °C and those of the rutile (tetragonal) structure at substrate temperatures above 600 °C for TiO2 thin films and the patterns attributable to the monoclinic structure with 〈−111〉 orientation for ZrO2 and HfO2 thin films. Scanning electron microscopy (SEM) observations show voided columnar structures with rough surfaces for TiO2 thin films and fine columnar structures with smooth surfaces for ZrO2 and HfO2 thin films, which is supported by the results obtained from atomic force microscopy (AFM) analysis. The quantitative data on the lattice strain, crystallite size, surface roughness, and refractive index are plotted against the homologous substrate temperature, Tsub/Tm (Tsub: substrate temperature and Tm: melting point of thin film materials). The lattice strain reaches approximately zero at Tsub/Tm = 0.3–0.35, suggesting that the residual stress is relaxed at this point, and the crystallite size reaches a plateau at the same range of Tsub/Tm. The surface roughness increases sharply after passing Tsub/Tm = 0.25–0.30, and the refractive index shows a rise at Tsub/Tm = 0.30–0.35. The images obtained by SEM and AFM are categorized based on the property transition observed in the quantitative property changes. The data obtained in this work are utilized to systematically study the effectiveness and appropriateness of the homologous (normalized) substrate temperature to explain the changes in structure, morphology, and properties of oxide thin films. Furthermore, it is suggested that the structure zone model, which is normally applied to sputtered metal films, is also applicable to sputtered oxide thin films.

Defect generation mechanism in magnetron sputtered metal films on PMMA substrates

Polymer metallization is widely used in a variety of micro and nano system technologies, and magnetron sputtering of a metal film is one of the essential processes of polymer metallization. However, some defects are likely generated in sputtered metal films on a polymer substrate. In this work, the defect generation mechanism in the sputtered Au film on a polymethylmethacrylate (PMMA) substrate was investigated for the first time. The characteristics of defects on the PMMA surface and in the Au film were examined by an optical microscope, a scanning electron microscope (SEM) and a confocal microscope. Detailed characterization results indicate that the ejected Au atoms bombard the PMMA substrate and cause snowflake-like defects on the PMMA surface because of the low hardness of PMMA, then Au atoms nucleate and grow at PMMA defect sites and form a partially suspended metal film, subsequently dropping the photoresist makes the suspended metal film conformally adhere to the PMMA defect, and the snowflake-like morphology is replicated to the metal film. The effects of sputtering parameters on the defects were studied, and the amount of defects in the Au film reduced with the decrease of the sputtering power or the sputtering pressure.

In Situ Electrochemical Cells to Study the Oxygen Evolution Reaction by Near Ambient Pressure X-ray Photoelectron Spectroscopy

In this contribution, we report the development of in situ electrochemical cells based on proton exchange membranes suitable for studying interfacial structural dynamics of energy materials under operation by near ambient pressure X-ray photoelectron spectroscopy. We will present both the first design of a batch-type two-electrode cell prototype and the improvements attained with a continuous flow three-electrode cell. Examples of both sputtered metal films and carbon-supported metal nanostructures are included demonstrating the high flexibility of the cells to study energy materials. Our immediate focus was on the study of the oxygen evolution reaction, however, the methods described herein can be broadly applied to reactions relevant in energy conversion and storage devices.

Sputtered Pt electrode structures with smoothly tapered edges by bi-layer resist lift-off

A lift-off process using a bi-layer resist consisting of an image reversal resist on top and a lift-off resist at the bottom was used to structure Ti–Pt thin films. DC magnetron sputtered metal films patterned by this process show ultra smooth edges, ideal for applications such as interdigitated electrodes in resistive gas sensors including thin-film based sensitive coatings with thicknesses below 100nm. Profiles of processed structures were analyzed by scanning electron microscopy and surface profilometer. The thickness profile and structure width were controlled by using different resist thicknesses and undercut lengths. Results were compared with iterative simulations by a geometric shadowing model, predicting undersputtering length and profile structure of the experimentally manufactured samples in good agreement. Target-to-substrate distance variation was found to have only a minor influence on the sputtering result.

Transferred metal electrode films for large-area electronic devices

The evaporation of metal-film gate electrodes for top-gate organic field-effect transistors (OFETs) limits the minimum thickness of the polymer gate dielectric to typically more than 300 nm due to deep hot metal atom penetration and damage of the dielectric. We show here that the self-release layer transfer method recently developed for high-quality graphene transfer is also capable of giving high-quality metal thin-film transfers to produce high-performance capacitors and OFETs with superior dielectric breakdown strength even for ultrathin polymer dielectric films. Dielectric breakdown strengths up to 5–6 MV cm−1 have been obtained for 50-nm thin films of polystyrene and a cyclic olefin copolymer TOPAS® (Zeon). High-quality OFETs with sub-10 V operational voltages have been obtained this way using conventional polymer dielectrics and a high-mobility polymer semiconductor poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene-2,5-diyl]. The transferred metal films can make reliable contacts without damaging ultrathin polymer films, self-assembled monolayers and graphene, which is not otherwise possible from evaporated or sputtered metal films.

Nanoscale growth twins in sputtered metal films

This article reviews recent studies on the mechanical properties of sputtered copper and 330 stainless-steel films with {111} nanoscale growth twins preferentially oriented perpendicular to growth direction. The mechanisms of formation of growth twins during sputtering, unusually high strengths, and excellent thermal stability of nanotwinned structures are highlighted.

Electrochemical promoted catalysis: Towards practical utilization

Electrochemical promotion (EP) of catalysis has already been recognized as 'a valuable development in catalytic research' (J. Pritchard, 1990) and as 'one of the most remarkable advances in electrochemistry since 1950' (J. O'M. Bockris, 1996). Laboratory studies have clearly elucidated the phenomenology of electrochemical promotion and have proven that EP is a general phenomenon at the interface of catalysis and electrochemistry. The major progress toward practical utilization of EP is surveyed in this paper. The focus is given on the electropromotion of industrial ammonia synthesis catalyst, the bipolar EP and the development of a novel monolithic electropromoted reactor (MEPR) in conjunction with the electropromotion of thin sputtered metal films. Future perspectives of electrochemical promotion applications in the field of hydrogen technologies are discussed.

Ultra-sensitive, highly reproducible film stress characterization using flexible suspended thin silicon plates and local curvature measurements

Film stress is crucial for stringent MEMS/NEMS design. In this paper, novel micromachined flexible suspended thin silicon plates combined with a sub-nanometer optical interferometry measuring setup have been developed to detect stresses in nanometer-scale films as well as ultra low stresses in thin films. By measuring the local out-of-plane curvature of a thin silicon substrate of 15 µm, a bending sensitivity two orders larger than that of the wafer curvature method has been achieved. Residual stresses in LPCVD Si3N4 thin films are measured, which are in good agreement with those extracted by other methods. Since non-contact optical instruments are used to detect all the parameters and the boundary conditions are well characterized, reproducibility better than 1% has been realized. By reusing the testing structures, residual stresses in sputtered metal films are also determined, which vary in a broad range. A stress difference as small as 1.5 MPa within a 30 nm film can be resolved with this metrology, which is among the best in the present reports.

Electrical and mechanical behaviour of improved platinum on ceramic bolometers

Bolometers using Au meanders on a mica substrate under irradiation suffered severe degradation before 0.01 dpa. Therefore this work was undertaken to examine alternative more radiation resistant bolometer versions. Basic prototypes from CIEMAT with sputtered Pt meander sensors on Al 2O 3 and AlN ceramic substrates were tested during electron and neutron irradiation at CIEMAT and SCK/CEN Mol. Results up to 0.01 dpa showed acceptable behaviour of both substrates and better radiation resistance response of Pt compared with Au. However the electrical connection between terminals and meander was identified as a weak point of the design. In addition the electrical response of the sputtered metal films was observed to degrade at high temperatures (≥900 °C) as a consequence of the discontinuity of the thin metal film and the formation of Pt islands. Here we report on an improved prototype, with reduced meander area, enhanced Pt film quality and adhesion, and better electrical connections. The improved bonding and hence stability of the meander was obtained by sputtering and thermally evaporating a Pt sensor on to polished surfaces of AlN and Al 2O 3 substrates. The thermal stability of the sputtered Pt deposit has also been followed using ESEM during in situ sample heating. After vacuum annealing at 400 °C, these new prototypes were electrically characterized.

一枚型イオンスパッタ金属膜によるき裂長さの測定

This research developed a simple and high precision method to measure the length of a fatigue crack using an extremely thin ion sputtered metal film based on that the electric resistance of the film changes with the increase of the crack. The electric resistance of a cracked film was calculated by the electrothermal FEM analysis. Based on the FEM analysis results, the relationship between the electric resistance and crack length is expressed by a practical formula. Fatigue crack length measurements for acrylic and metal test specimens were performed on the three-points fatigue test equipment. Based on the good agreements between the measurement results by the ion sputtered film and that by the optical microscope, it is clarified that the crack length measurement method with an ion sputtered metal film has a very high precision. In addition that the measurement system is very simple, this method can be said to have a high practical usability.

Novel Structured Metal Film Growth by Glancing Angle Sputter Deposition

It is well known that a sputtered metal film grows with inclined columns when the incident angle of sputtered particles inclines to the substrate normal. This phenomenon is usually explained by so-called self-shadowing effect. We have shown that the novel structured film, such as zigzag and/or helical columnar structure along with the growth direction, can be grown by changing the incident angle of sputtered particles into substrates during deposition. The relationship between sputtering conditions and film structures has also been investigated. Furthermore, the contact angle of a water drop on the Cr films with helical columnar structure was found to be much smaller than that on the inclined columnar film. This suggests that we can control the characteristics of surface by coating these novel columnar structured films.

113 金属薄膜を用いたき裂長さ測定(OS1-4 き裂の評価・計測技術,OS1 機能性材料の損傷とその力学的背景)

113 金属薄膜を用いたき裂長さ測定(OS1-4 き裂の評価・計測技術,OS1 機能性材料の損傷とその力学的背景)

Gas-tight alumina films on nanoporous substrates through oxidation of sputtered metal films

The fabrication of ultrathin oxide films without gas leakage was investigated for the application to low-temperature solid oxide fuel cells (SOFCs). Aluminum thin films were deposited onto two types of anodic nanoporous alumina substrates with pore diameter of 20 and 200 nm, respectively, using dc-magnetron sputter at room temperature. By subsequent oxidation at temperatures over 500 °C, the metal films were successfully transformed into oxide films with thickness of about 35 and 410 nm. Volume expansion induced from oxidation of metal resulted in dense thin films that are free from hydrogen permeation.

スパッタリング金属膜によるき裂長さの測定(OS2 機械要素の設計・製造・応用技術)

スパッタリング金属膜によるき裂長さの測定(OS2 機械要素の設計・製造・応用技術)

Copper indium disulfide solar cell absorbers prepared in a one-step process by reactive magnetron sputtering from copper and indium targets

Reactive magnetron sputtering from copper and indium targets in argon-hydrogen sulfide mixtures has been used to prepare CuInS 2 absorbers for thin film solar cells. Compared with the sequential process, where sputtered metal films are sulfurized, this technique offers the advantage of a one-step process. The influence of substrate temperature, total sputtering pressure and the copper-to-indium ratio on structure and morphology was investigated. The argon-to-hydrogen sulfide ratio was fixed at 1:1. Lower sputtering pressure and higher substrate temperature lead to larger crystal grains. The films were prepared copper-rich and exhibited only the CuInS 2 (roquesite) and the CuS (covellite) phases. Due to the phase separation, known from the growth of copper-rich CuInS 2 films, the metallic CuS phase on top of the as grown films could be removed by wet-chemical etching. As in the case of the sequential process or of coevaporated films, the copper-to-indium ratio has a strong influence on grain size and electronic properties. First solar cells prepared with these absorber films exhibited a maximum efficiency of 6.4% at AM1.5 illumination. The diffusion length in the first cells prepared from reactive magnetron sputtered absorbers are three to four times lower than that of coevaporated CuInS 2 films. However, this ion assisted deposition process offers the possibility to prepare absorber films at lower temperatures compared with a thermally activated process, like sulfurization or coevaporation. Furthermore, the presented results are a further step towards a continuous vacuum process for CuInS 2–thin film solar cell preparation.

Nanoscratch Behavior of Sputtered Metal Films on PAMAM Dendrimer Monolayers

ABSTRACTStriking differences have been observed in the deformation modes associated with 2mN constant load nanoscratch events on ultrathin Cr layers deposited on SiOx with and without a dendrimer interlayer. In the absence of the dendrimer distinct ridge formation along the wear track indicative of plowing and wedge formation are observed. By contrast, dendrimer monolayer-mediated films exhibit ridgeless scratches apparently formed in a nearly pure cutting mode. In addition, the width of the scratch trench in the sample without dendrimer is larger than the one with dendrimer.

Specular and diffuse electron scattering at interfaces in metal spin-valve structures

We have made thickness dependent in situ resistivity measurements on sputtered metal films in real time during film deposition. These measurements allow the separation of the bulk and finite-size contributions to the resistance. The metals studied were Co, Cu, Ni80Fe20, and Ta, deposited in differing orders to isolate the scattering at interfaces relevant to common spin-valve structures. We see sources of excess diffuse scattering in bilayers of Ta with the 3d metals, regardless of the deposition order. We see a similar effect for Co on Cu, but not for Cu on Co. In some cases, we see significant changes in film resistance from overlayers as thin as 2 Å. These results show that the two Cu interfaces in a spin valve are not equivalent, and that other interfaces in the structure may be important. We discuss the origin of the diffuse scattering in terms of interdiffusion or a roughening transition during the initial deposition and island coalescence.

Electrochemical process for advanced package fabrication

Interconnections for high-end applications are essentially low-resistance transmission-line structures with precisely controlled cross-sectional shapes and dimensions. The relatively thick copper conductors-typically 6 µm or more-combined with the stringent control required on the 10-20-µm-wide cross sections stretches the capabilities of the subtractive etch and lift-off processes that are typically used in semiconductor fabrication to pattern evaporated and sputtered metal films. Electroplating through a photoresist mask, which has proven itself to be a highly effective, precision manufacturing process for thin-film magnetic recording heads, is, however, capable of meeting and far exceeding the requirements of package fabrication. This paper describes the fabrication of a package structure that integrates traditional dry-process technologies with electrolytic copper plating to form the conductors, polyimide backfill and planarization steps to form the dielectric, and electroless deposition to selectively clad the copper lines to prevent adverse reaction of the copper with water generated during the polyimide cure. The discussion highlights salient issues which are pertinent to the compatibility of the individual process steps and to the extension of the technology to more demanding packaging structures and to other applications.