High-rate Sputtering Research Articles

Preparation of TiO2 Thin Film Photocatalyst by High-rate Low-temperature Sputtering Method

After depositing an ultra-thin metallic Ti film by sputtering, we repeated the process of exposing the still active plasma gas for high-rate low-temperature deposition of a metal compound film, thereby successfully fabricating a thin film of TiO2 with photocatalytic properties. The TiO2 thin film produced using the present method exhibited approximately 15 times the deposition rate of DC reactive magnetron sputtering, yielding a crystalline structure using an unheated substrate (approximately 40°C).

High-Rate Sputtering of Si and SiO<sub>2</sub> with Atomically Flat Surfaces by Using Ethanol Cluster Ion Beams

High-Rate Sputtering of Si and SiO<sub>2</sub> with Atomically Flat Surfaces by Using Ethanol Cluster Ion Beams

Improvement of depth resolution in XPS analysis of fluorinated layer using C 60 ion sputtering

Depth profile of C 60 ion-used X-ray photoelectron spectroscopy (XPS) was studied on fluorinated organic layers with different thicknesses. We found that the depth resolution decreased, the sputtering rate went down and the surface turned rough as the layer thickness increased. This is because carbon-rich layer was formed on the surface by cross-linking reaction of the polymer and/or accumulation of degraded C 60 through continuous sputtering. Surprisingly, the high sputtering rate drastically improved the resolution of the analysis. The rate over 48.7 nm/min did not show any deterioration on the depth resolution, the sputtering rate and surface smoothness.

Influence of sputter rate and crystal orientation on the distribution of carbon in polycrystalline copper surfaces treated by plasma immersion ion implantation

The sputter rate influences the resulting thickness of the carbon containing layer within a surface that was treated by plasma immersion ion implantation. Choosing a polycrystalline substrate with rather large crystals and a material with an inherent high sputter rate, inhomogeneous distributions of carbon over the substrate area due to different thicknesses of the incorporated carbon can be detected. A correlation of three factors namely the carbon x-ray intensity in electron probe microanalysis, the thickness of the carbon layer, and the sputter rate in depth profiling measurements via secondary ion mass spectrometry can be shown. Essential for these factors is the crystal orientation that is visualized by mapping via electron backscatter diffraction. The differences in carbon content due to the orientation are most likely one of the reasons that the adhesion of diamond-like carbon films on copper does not improve with an interlayer of implanted carbon.

High rate sputtering deposition of silicon oxide thin films from new SiO2:Si target composition

The authors have developed an electrically conductive sputtering target by a sintering process using powders of SiO2 and boron doped Si. This target composition can be sputtered using dc, pulse dc, or rf power supplies. Using rf sputtering the authors have demonstrated deposition rates that are four times higher than typical deposition rates for rf sputtered SiO2 films from quartz targets. Further, the optical transmittance, refractive index, microstructure, and etching resistance of the SiO2 films prepared using this target are comparable to films produced from rf sputtered quartz targets. In this article, the authors present details of the conductive SiO2:Si target composition as well as the resulting SiO2 film properties and deposition rates that have been achieved. They also discuss the possible mechanisms for such high deposition rates.

Stability of thin film transistors incorporating a zinc oxide or indium zinc oxide channel deposited by a high rate sputtering process

A novel rf sputtering technology in which a high density plasma is created in a remote chamber has been used to reactively deposit zinc oxide (ZnO) and indium zinc oxide (IZO) thin films at room temperature from metallic sputtering targets at deposition rates ∼50 nm min−1, which is approximately an order of magnitude greater than that of rf magnetron sputtering. Thin film transistors have been fabricated using IZO with a maximum processing temperature of 120 °C, which is defined by the curing of the photoresist used in patterning. Devices have a saturated field effect mobility of 10 cm2 V−1 s−1 and a switching ratio in excess of 106. Gate bias stress experiments performed at elevated temperatures show a consistent apparent increase in the field effect mobility with time, which is attributed to a charge trapping phenomenon.

Preparation of CrN thick films by high-rate middle-frequency unbalanced magnetron sputtering

A middle-frequency (MF) unbalanced magnetron sputtering system equipped with an electron source was designed and used for deposition of CrN thick films under various MF power (1.4–14 kW) at fixed temperature, pressure, and gas flow rate. The deposition rate was increased with increasing MF power and the structure and N/Cr ratio of the deposited CrN films exhibited a complicated behavior, where the CrN films were a polycrystalline structure and the films deposited under optimized conditions exhibited a dense columnar structure and a micro-hardness of 16 GPa. The dependence of the structure and micro-hardness on MF power was interpreted by the power deposition efficiency.

Deposition and focused ion beam milling of anticorrosive CrC coatings on tool steel substrates

For micro replication, the base of a die should be ductile and the surface layer that will undergo processing should have a good machining response to various tool-making processes. At the same time, the resulting working surfaces of the tooling cavities should be hard; having low roughness, low wettability and high erosion resistance. To achieve such diverse properties, nano-crystalline CrC coatings deposited onto 12% Cr tool steel were investigated in this research. To verify the properties of such coatings various metallographic techniques were applied. In particular, the corrosion resistance was studied by means of potentiodynamic anodic polarisation. A scanning transmission electron microscopy analysis of the structure was performed on samples prepared with focused ion beam (FIB) machining. The mechanical properties and grain size distribution were determined and statistically analysed. In addition, X-ray diffraction, scanning electron microscopy and atomic force microscopy were used in studying the surface properties of these coatings. To investigate the response of the CrC coatings to micro- and nano-structuring technologies with high specific energy, a series of rectangular trenches were produced by FIB milling. The effects of the ion beam current, exposure time and ion fluence on the sputtering yield and roughness of the produced micro-structures were especially investigated. Some essential parameter windows for performing FIB milling with relatively high sputtering rates, higher than 1 µm/min, and at the same time achieving the best possible surface integrity were determined during the experiments.

Reactively sputtered ZrN for application as reflecting back contact in Cu(In,Ga)Se 2 solar cells

We investigate reactively sputtered films of zirconium nitride, ZrN, for use as highly reflecting back contacts in Cu(In,Ga)Se 2 (CIGS) devices with sub-micrometer absorbers. We identify the nitrogen flow and the sputter current as the decisive parameters for the composition, and demonstrate a method for determining the nitrogen flow at which the transition from metallic to compound sputtering mode occurs for a given current. Films prepared at this working point consist of stoichiometric ZrN with a low resistivity, a high reflectance for red and infrared light, and have a fairly high sputter rate. Calculations show that the reflectance at the ZrN/CIGS interface is significantly superior to that at the standard Mo/CIGS interface.

High-speed processing with Cl2 cluster ion beam

Cluster ion beam processes can produce high rate sputtering with low damage compared with monomer ion beam processes. Cl2 cluster ion beams with different size distributions were generated with controlling the ionization conditions. Size distributions were measured using the time-of-flight (TOF) method. Si substrates and SiO2 films were irradiated with the Cl2 cluster ions at acceleration energies of 10–30keV and the etching ratio of Si/SiO2 was investigated. The sputtering yield increased with acceleration energy and was a few thousand times higher than that of Ar monomer ions. The sputtering yield of Cl2 cluster ions was about 4400atoms/ion at 30keV acceleration energy. The etching ratio of Si/SiO2 was above eight at acceleration energies in the range 10–30keV. Thus, SiO2 can be used as a mask for irradiation with Cl2 cluster ion beam, which is an advantage for semiconductor processing. In order to keep high sputtering yield and high etching ratio, the cluster size needs to be sufficiently large and size control is important.

Selective formation of competitive c-axis and a-axis oriented LiNbO3 epitaxial films on Al2O3(112¯0)

The crystallographic orientation of epitaxial LiNbO3 films on the Al2O3(112¯0) substrate can be controlled either toward the c-axis or a-axis depending on the situation at crystallization. Crystallization during high-rate sputter deposition at elevated temperatures produced c-axis-oriented film with 60°-rotated twin domains. Minimizing the surface energy when the growing surface was exposed to abundant ion flux selected (0001) terminated mosaic crystal. In contrast, solid-phase crystallization or as crystallization during a low-rate sputter deposition yielded a-axis-oriented film coexisting with 180° polarization twin domains. The enhanced migration of atoms in low-density amorphous film as well as pseudomorphic lattice matching growth under thermal equilibrated conditions led to the self-organization of relaxed crystalline domains.

Role of cathode identity in liquid chromatography particle beam glow discharge mass spectrometry

A detailed evaluation of the role of cathode identity on the analytical and spectral characteristics of various organic, organometallic and metal analytes using liquid chromatography–particle beam/glow discharge mass spectrometry (LC–PB/GDMS) has been carried out. A d.c. discharge, operating with argon as the support gas, was used throughout this work. In this study, Cu which has a relatively high sputtering rate, Ni which has moderate sputtering rate and Ta which has very low sputtering rate, are taken as cathode materials to study the ionization, fragmentation, and analytical characteristics of organic (caffeine, epigallocatechin gallate, peptide as representative compounds), organometallic (selenomethionine, triethyl lead chloride as representative compounds) and metal (Fe, La, Cs and Pb) species. A range of discharge gas pressures (26.6–106.4 Pa) and currents (0.2–1.5 mA) were investigated with the test cathodes to determine their influence on the spectral composition and overall analytical response for the various test species. Calibration plots were obtained for all of the species for each of the three cathodes to determine the respective limits of detection. Relative detection limits in the range of 0.02 to 15 ng mL − 1 (0.002–1.5 ng, absolute) for the test species were found to be in the order of Cu > Ni > Ta; which follows the order of the sputtering characteristics of the respective cathodes. These studies rendered information about the respective discharge parameters' role in choosing the most appropriate cathode identity in PB-GDMS for application in the areas of organic, organometallic and inorganic species analysis.

High-Speed Nanoprocessing with Cluster Ion Beams

Cluster ion beam processes can produce higher rate sputtering with lower damage compared with monomer ion beam processes. In particular, it is expected that extreme high-rate sputtering can be obtained using reactive cluster ion beams. Several kinds of hydrofluorocarbon (HFC) (CF4, CHF3, and CH2F2) and Cl2 gas clusters were generated, and their cluster size distributions were measured using the time-of-flight (TOF) method. Si substrates were irradiated with the reactive cluster ions at acceleration energies in the range of 5-80 keV. The sputtering yield increased with acceleration energy and was about 1000 times higher than that of Ar monomer ions for comparable conditions. Despite the very high sputtering yields, a Si surface irradiated by reactive cluster was smoothed. This high-speed processing with reactive cluster ion beam can be applied to fabricate nanodevices.

Onset of hard magnetic L1 0 FePt phase with (001) texture

The perpendicular anisotropic magnetic properties of in-situ deposited FePt/Pt/Cr trilayer films were elucidated as functions of the deposition temperature and the sputtering rate of the FePt magnetic layer. Ordered L1 0 FePt thin films with perpendicular anisotropy and a (001) texture can be developed at a temperature as low as 300 °C with the sputtering of a FePt layer at a low rate. The larger Pt(001)[100] lattice induced an expansion of the FePt a- and b-axis, leading to the contraction of the FePt c-axis, enabling the epitaxial growth of the L1 0 FePt(001) texture to occur. A low rate of sputtering of the FePt thin film promotes the formation of the magnetically hard FePt(001) texture on the surface of the Pt(001) buffer layer at low temperature, while the high sputtering rate of FePt layer suppresses the phase transformation.

Growth Mechanism of Indium Tin Oxide Whiskers Prepared by Sputtering

Whisker structures of indium tin oxide were prepared on a glass substrate by conventional sputtering using an indium-tin alloy target. Whisker structures grew well at higher temperatures than the crystallization temperature of In2O3 and the melting temperature of the In–Sn alloy, and also under the sputtering conditions of comparatively scarce oxygen and a high sputtering rate. These sputtering conditions correspond to the transition mode of reactive sputtering. The whisker structures were categorized into a structure consisting of many needles and a structure consisting of many trunks with side branches. Each whisker was a bcc single crystal growing along the <222> direction and had a spherical droplet-like structure on the tip. Consequently, it was revealed that In–Sn droplets acted as important cores of whisker growth. The indium tin oxide (ITO) whiskers were grown by a self-catalytic vapor–liquid–solid mechanism promoted by the supersaturation of indium vapor.

Energy distribution of high-energy cluster ion beams

Cluster ion beam processes can produce special surface modification effects, such as surface smoothing, high rate sputtering and very shallow implantation. In order to realize high-speed surface processing, a high-energy gas cluster ion beam irradiation system was developed. Since cluster energy depends on chamber pressure, the energy distribution of the high-energy cluster ion beams was measured for various pressure regimes. These distributions show that both cluster size and energy decrease with increasing collisions with residual gas. The number of atoms scattered by one collision with residual gas is proportional to the velocity of the cluster ion. The results suggest that an analytical equation can be used to calculate irradiation energy from the acceleration energy, size of cluster, chamber pressure and transportation length.

Substitution of transparent conducting oxide thin films for indium tin oxide transparent electrode applications

The present status and prospects for further development of reduced or indium-free transparent conducting oxide (TCO) materials for use in practical thin-film transparent electrode applications such as liquid crystal displays are presented in this paper: reduced-indium TCO materials such as ZnO-In2O3, In2O3-SnO2 and Zn-In-Sn-O multicomponent oxides and indium-free materials such as Al- and Ga-doped ZnO (AZO and GZO). In particular, AZO thin films, with source materials that are inexpensive and non-toxic, are the best candidates. The current problems associated with substituting AZO or GZO for ITO, besides their stability in oxidizing environments as well as the non-uniform distribution of resistivity resulting from dc magnetron sputtering deposition, can be resolved. Current developments associated with overcoming the remaining problems are also presented: newly developed AZO thin-film deposition techniques that reduce resistivity as well as improve the resistivity distribution uniformity using high-rate dc magnetron sputtering depositions incorporating radio frequency power. In addition, stability tests of resistivity in TCO thin films evaluated in air at 90% relative humidity and 60 °C have demonstrated that sufficiently moisture-resistant AZO thin films can be produced at a substrate temperature below 200 °C when the film thickness was approximately 200 nm. However, improving the stability of AZO and GZO films with a thickness below 100 nm remains a problem.

Observation of a Si surface sputtered by an ion irradiation system using a prototype compact cluster ion source

A prototype compact cluster ion source has been developed using a metal cluster complex as a low damage-sputtering source, since clusters are said to be effective for so-called “lateral sputtering”. Using a metal cluster complex ion gun the Si surface was successfully sputtered with high sputtering yield, and yet resulting in reasonably smooth surface for a sputtered depth of 10 nm. Using the prototype compact cluster ion source, an ion beam containing metal cluster complexes of Os 3(CO) 12 was generated with an acceleration energy of 10 keV and total fluence, N CB, of 5.2 × 10 12 ions ( I ave = 0.050 nA, time = 278 min). From the results of AFM and SEM measurements, the sputtered Si surface was found to be reasonably smooth for a sputtering depth of ∼ 10 nm. The sputtered Si portion was found to be a truncated (elliptical) cone. The volume was estimated to be 3.2 × 10 −9 cm 3, i.e., N Si, the number of removed Si atoms was about 1.6 × 10 14. Thus the sputtering yield, N Si/ N CB, was estimated to be as large as 30. Surface state characterization and contamination were investigated using XPS (X-ray photoelectron spectroscopy) and AES (Auger electron spectroscopy), showing there was no Os on the sputtered Si surface. These results show that this ion irradiation system using a prototype compact cluster ion source is capable of high rate sputtering resulting in a smooth sputtered surface without deposition, showing the possibility for small penetration depth leading to low damage sputtering, in other words, lateral sputtering due to simultaneous multi-atom bombardment.

Surface processing with high-energy gas cluster ion beams

Gas cluster ion beams can produce high rate sputtering with low damage compared with the more familiar monomer ion beam process. In order to realize high-speed surface processing, a high-energy gas cluster ion beam irradiation system was developed in which high-energy Ar cluster ion beams were generated. The mean size of the Ar cluster was about 1800 atoms, as measured using the time-of-flight (TOF) method. Si substrates were irradiated with the Ar cluster ions at acceleration energies between 20 and 80 keV. The sputtering yield increased with acceleration energy and reached about 230 atoms/ion at 80 keV, a value about 180 times higher than that of Ar monomer ions. Au films were also irradiated at acceleration energies between 20 and 80 keV and the surfaces were observed with Atomic Force Microscopy (AFM). The high-energy cluster ion irradiation caused a decrease in surface roughness. These results indicate that high-speed smooth etching can be realized with high-energy cluster ion beams. This processing method can be applied to fabricate nano-devices.

High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO2thin films using dc dual magnetron (DM) sputtering in Ar + O2mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature Tsurfmeasured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency frwas investigated in detail. It was found that the increase of frfrom 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate aDof sputtered TiO2films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO2films can be sputtered on unheated glass substrates at aD = 80 nm/min, Tsurf < 180 °C when high value of fr = 350 kHz was used. Properties of a thin hydrophilic TiO2film deposited on a polycarbonate substrate are given.