High-purity Thin Films Research Articles

Growth mechanism and electrical properties of tungsten films deposited by plasma-enhanced atomic layer deposition with chloride and metal organic precursors

We compared the growth characteristics and film properties of tungsten (W) thin films prepared by atomic layer deposition (ALD) using two newly synthesized precursors, tungsten pentachloride (WCl5) and ethylcyclopentadienyltungsten(V) tricarbonyl hydride (HEtCpW(CO)3), with Ar/H2 plasma as the reactant. The purpose of this study was to evaluate the suitability of these precursors for W thin films used in interconnect technology. The growth characteristics and film properties were significantly affected by the ligands of the precursors. The chemical compositional analysis results showed that high-purity thin films were obtained using the WCl5 precursor, compared to the films obtained using the HEtCpW(CO)3 precursor, which were relatively high in carbon content and oxygen impurities. The W thin films obtained from the WCl5 precursor showed superior electrical properties compared to those of the HEtCpW(CO)3 precursor, which were related to the crystallinity and film density in addition to the impurities. These results provide profitable information regarding the selection of a pertinent precursor for the device fabrication.

Atomic Layer Deposition of Catalytic Manganese Oxide for High Surface Area Zinc-Air Battery Electrodes

Driven by the need to move away from the use of fossil fuels, clean energy technologies such as wind and solar have seen tremendous technological and economic development in the last decade. The rapidly falling cost of wind and solar energy has made these technologies economically competitive with fossil fuels, promoting large growth. Renewable energy grew by 14.1% in 2016 alone.[1,2] With the continuing growth of renewable technologies, comes the need for cheap, safe and reliable energy storage solutions. Currently Li-ion batteries are seeing widespread use for renewable energy storage. However, the use of metallic Li in these batteries makes them expensive and unsafe. Zinc-air batteries are an attractive alternative to Li-ion batteries because they are inexpensive, safe, environmentally benign, and have excellent energy density.[3] The cathode for Zn-air batteries has a number of design requirements in order to facilitate the reduction of oxygen from the air. The cathode must be hydrophobic and porous to allow for diffusion of oxygen into the cell while maintaining intimate contact with the electrolyte within the cell. It also must be conductive and have sufficient loading of an effective catalyst to improve the poor kinetics of the oxygen reduction reaction. Catalyst distribution on/in the cathode is very important as well, as effective surface area of the catalyst is critical to battery performance. Since the oxygen reduction reaction utilizes oxygen from the air, three phase boundaries between air, electrolyte, and catalyst are of key importance.[3] Atomic layer deposition (ALD) is a gas phase deposition technique capable of producing high purity thin films of a wide variety of materials. The development of ALD techniques has largely been driven by the strict material and design challenges of the semiconductor industry. ALD utilizes alternating pulses of reactants that each undergo self-limiting reactions on the sample surface. These self-limiting reactions give rise to a number of useful properties of ALD films such as uniformity, conformality, composition control and thickness control on the order of Ångstroms.[4] ALD can be used to deposit catalytic material directly onto high surface area electrodes, such as porous carbon paper, so that the internal surfaces of the electrode can all be coated. By coating the entire porous structure of the electrode, the effective catalyst surface area and three phase boundary area can be greatly increased. In this work, an ALD process is developed to deposit Mn oxide (MnOx) catalytic films directly onto porous carbon for application as the air electrode in Zn-air batteries. Initial depositions are conducted on Si wafers so that in-situ spectroscopic ellipsometry can be used to monitor deposition behavior. Once optimal ALD parameters are finalized, MnOx films of varying thicknesses are prepared on carbon electrodes and tested for their reactivity towards the oxygen reduction reaction. MnOx has a variety of oxidation states and crystal structures, each with varying degrees of catalytic activity. In order to maximize performance, various deposition and annealing conditions will be used to generate different MnOx phases. Deposits are characterized using a variety of electrochemical and materials techniques including linear sweep voltammetry, electrochemical impedance spectroscopy, galvanostatic cycling, scanning and transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and Raman spectroscopy. [1] BP Statistical Review of World Energy 66th Edition, June 2017 [2] G. Jifan, “The next energy revolution is already here”, World Economic Forum, September 20 2017, [online] https://www.weforum.org/agenda/2017/09/next-energy-revolution-already-here/ [3] J. Lee, S. T. Kim, R. Cao, N. Choi, M. Liu, K. T. Lee, “Metal–Air Batteries with High Energy Density: Li–Air versus Zn–Air”, Adv. Energy Mater., 1 (2011) 34-50 [4] S. M. George, “Atomic Layer Deposition: An Overview”, Chem. Rev., 110 (2010) 111-131

Flash-Lamp-Enhanced Atomic Layer Deposition of Thin Films

Atomic Layer Deposition (ALD) is a particular thin film deposition technology which is based on alternating saturated surface reactions. As a result, the film growth proceeds in a self-limiting manner enabling the deposition of thin films with excellent thickness control, uniformity, and conformity. Although a large number of materials have been deposited by ALD so far for various applications, there are still some challenges in ALD.The deposition temperatures in ALD are typically lower compared to CVD due to the limited thermal stability of ALD precursors. As a consequence of the lower energy available for film formation the films may not meet the properties needed for application. In these cases a post deposition annealing is required to improve the film properties, e.g. to obtain the desired film structure, density, or purity. However, this high temperature processing is often impracticable due to a restricted thermal budget of the substrate, in particular when coating temperature sensitive substrates. Secondly, the reactants of an ALD process, e.g. oxygen, may react with the substrate itself leading to the formation of a parasitic interfacial layer. In order to avoid this issue, the proper choice of reactants or the use of an alternative deposition technique is essential. Furthermore, many ALD processes suffer from substrate inhibited film growth accompanied by inefficient precursor consumption and the formation of films with unfavorable properties. Finally, there are materials of interest, e.g. titanium, which so far can not be deposited by thermal ALD at all. These limitations may be overcome by the application of flash lamp annealing (FLA) in ALD.In FLA the substrate is exposed to a light flash with durations typically in the millisecond range. The light energy is absorbed within the top layers of the sample causing a rapid heating of the surface near region. On the contrary, the bulk material experiences no or only moderate heating. Consequently, FLA is a suitable technology to power high temperature processes even on temperature sensitive substrates.The film growth in flash lamp enhanced ALD is induced by this effect. Thereby, each process cycle consist of both a precursor pulse and the irradiation of the substrate with a light flash. During each single flash the surface temperature exceeds the threshold temperature which is required to achieve the thermal decomposition of adsorbed precursor molecules or to activate chemical reactions between the adsorbed precursor molecules and a second reactant. The film growth proceeds step-by-step and thus the film thickness can be controlled by varying the number of cycles. In addition, FLA in each cycle results in the periodical annealing of the already grown film and hence may lead to an improved film quality. Consequently, flash lamp enhanced ALD has a high potential for the realization of single-source processes, for the reduction of growth delay in the initial phase of film growth, for the deposition of high purity thin films, and for the deposition of new materials.In this work the principle of flash lamp enhanced ALD will be presented in detail, the technology will be reviewed and classified. Thereafter, we will give an overview about our studies on the flash enhanced ALD of aluminum-, ruthenium-, and tantalum-based thin films. These depositions were realized by flashing periodically on a substrate during the precursor pulses. We will show that the film growth is induced by the flash heating and the processes exhibits typical ALD characteristics. The obtained relations between flash parameters and film growth parameters will be discussed with the use of simulation results illustrating the temperature profile during the FLA treatment. Moreover, this work addresses the potentials of this technology as well as the technical challenges.

Investigation of the SiC thin films synthetized by Thermionic Vacuum Arc method (TVA)

Thermionic Vacuum Arc method (TVA) was used for the first time to prepare SiC thin films. This method is very suitable for deposition of high purity thin films with compact structure and extremely smooth in vacuum conditions. The nanocomposites were investigated using Transmission Electron Microscopy (TEM) analyses provided with HR-TEM and SAED facilities. The structure of the films can be indexed as following three forms: cubic structure of SiC (F4-3m) a = 0.4348 nm, cubic Si (Fd3m) a = 0.54307 nm and graphite (P63/mmc) a = 0.2456 nm; c = 0.6696 nm. The morphology, topography, wettability and wear properties were also performed by SEE system and by Raman Spectroscopy, increasing the interest for emerging applications.

TiN증착 조건에 따른 박막의 특성에 대한 실험적 연구

PVD방식에 의한 TiN박막의 형성은 DC와 RF sputtering deposition 방식을 적용할 수 있지만, 플라즈마 생성을 위해 주입된 가스의 이온화율이 떨어져 박막성형 속도가 느려지며, 박막과의 접착력을 높이는 것에도 한계성을 가지고 있다. 이를 개선하기 위해 증착과 동시에 이온빔을 조사하는 이온빔 진공증착 IBAD(Ion beam assisted deposition)를 이용 하게 되면, 코팅 전에 소재 표면을 Ion beam으로 조사하기 때문에 표면cleaning의 효과가 크고, 접착력이 높은 박막을 얻을 수 있다. 또한 고 진공과 낮은 온도에서도 균일한 두께의 고순도의 박막을 얻을 수 있는 이점이 있다. 【Formation of TiN films by PVD method and the DC and RF sputtering deposition method can be applied, the injected gas to generate plasma ionization rate of the film forming speed is slow away, anything to increase the adhesion between films limitations have. To improve this, to investigate the deposition and ion beam evaporation simultaneously IBAD(Ion beam assisted deposition) when used, Ion beam surface coating material prior to the survey because the surface cleaning effect of a large, high film adhesion can be obtained. In addition, the high vacuum and low temperature, high purity thin film of uniform thickness in the benefits is.】

Ce(IV) Complexes with Donor-Functionalized Alkoxide Ligands: Improved Precursors for Chemical Vapor Deposition of CeO2

Thin films of ceria (CeO(2)) have many applications, and their synthesis by liquid-injection MOCVD (metal-organic chemical vapor deposition) or ALD (atomic layer deposition) requires volatile precursor compounds. Here we report the synthesis of a series of homoleptic and heteroleptic Ce(IV) complexes with donor-functionalized alkoxide ligands mmp (1-methoxy-2-methylpropan-2-olate), dmap (1-(dimethylamino)propan-2-olate), and dmop (2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-olate) and their potential as precursors for MOCVD and ALD of CeO(2). New complexes were synthesized by alcohol exchange reactions with [Ce(OBu(t))(4)]. [Ce(mmp)(4)] and [Ce(dmap)(4)] were both found to be excellent precursors for liquid-injection MOCVD of CeO(2), depositing high purity thin films with very low carbon contamination, and both have a large temperature window for diffusion controlled growth (350-600 °C for [Ce(mmp)(4)]; 300-600 °C for [Ce(dmap)(4)]). [Ce(mmp)(4)] is also an excellent precursor for liquid-injection ALD of CeO(2) using H(2)O as oxygen source and demonstrates self-limiting growth from 150 to 350 °C. [Ce(dmap)(4)] has lower thermal stability than [Ce(mmp)(4)] and does not show self-limiting growth in ALD. Heteroleptic complexes show a tendency to undergo ligand redistribution reactions to form mixtures in solution and are unsuitable as precursors for liquid-injection CVD.

Highly enhanced electrochemical performance of silicon-free platinum–yttria stabilized zirconia interfaces

In the drive to achieve economically viable solid oxide fuel cells, efforts have been directed towards substantially decreasing their operating temperature. Unfortunately, these efforts have been hindered by extremely sluggish electrode kinetics at reduced temperatures. In this report, we show that silicon impurities on the surface of the electrolyte play a critical role in influencing electrode kinetics. More specifically, improvements by as much as three orders of magnitude are reported for the performance of platinum electrodes on yttria-stabilized zirconia electrolytes prepared as high purity thin films with a largely Si-free surface. These improvements in performance are estimated to enable operation of a solid oxide fuel cell down to approximately 400 °C.

Differential cross-section measurements for the 12C(d, p0)13C reaction and applications to surface analysis of materials

This work involves surface analysis by nuclear techniques, which are non-destructive, and computer simulation. The “energy analysis” method for nuclear reaction analysis is used. Energy spectra are computer simulated and compared to experimental data, giving target composition and concentration profile information. Measured values are presented for the differential cross-section of the 12C(d,p0)13C reaction in the deuteron energy range 0.81–2.07MeV for laboratory detection angles of 165° and 135°, using self-supported two-layered targets consisting of high purity thin films of typically 13μg/cm2 natural carbon and 65μg/cm2 gold. The error in the absolute differential cross-section values is generally ∼6%. The method, using these values, is successfully applied to determination of uniform concentration profiles of 12C, along considerable depths, for a thick flat target of high purity pyrolitic graphite. It is characterised a thin surface film of carbon on a thick flat quartz target. Uniform concentration profiles of 16O are also obtained from (d,p) and (d,α) reactions.

High purity Si–C–N thin films with tailored composition on the tie line SiC–Si 3N 4

Si–C–N thin films with tailored stoichiometries on the tie line SiC–Si 3N 4 have been produced by severalfold ion implantation and by a combination of RF magnetron sputtering and ion implantation, respectively. These high purity thin films have been heat treated at 1250 °C under high vacuum conditions using an electron beam annealing system to enable crystallisation and/or phase formation. Fourier transform infrared spectrometry as well as X-ray photoelectron spectroscopy suggests the formation of an amorphous network of mixed Si(C,N) 4 tetrahedrons for the ternary compositions and evince the crystallisation of the binary SiC and Si 3N 4 thin films.

Structure and luminescence of BaFBr:Eu2+ and BaFBr:Eu2+, Tb3+ phosphors and thin films

The inclusion of Tb3+ ions doped into the storage phosphor BaFBr:Eu2+ results in increased purity of the host material as well as an improvement in the linearity of the photostimulated luminescence (PSL) intensity versus the x-ray irradiation dose. Films produced by pulsed laser deposition (PLD) also show similar results, indicating that PLD is a powerful technique for producing high quality, high purity thin films. As a result, the PSL dose response is more linear in the thin films than in the powder samples. The emission intensity of Eu2+ in the phosphors increases with the increasing time of x-ray irradiation while the emission intensity of Tb3+ remains almost constant. This result may be explained by considering the reduction of impurity Eu3+ ions following trapping of the photoexcited electrons. The results demonstrate that these materials are not only potentially useful for medical imaging but also show promise for use in radiation dosimetry.

Formation of High Purity Films by Negative Ion Beam Sputtering Using an Ultra-high Vacuum Self-Sputtering Method

A high purity thin film deposition method has been established, which consists of ion beam sputtering with negative ions. The most important characteristic of this method is that high purity film synthesis by self-sputtering occurs under an ultra-high vacuum: this results in deposited films that contain no gas elements such as Ar and Kr, which are found using standard general sputtering apparatus. This is made possible by the negative ion source of the Cs sputter type which needs no discharge gas. In this report the formation of Si, Si-C and Si-Fe films is demonstrated. The purity of deposited films is analyzed using the Rutherford backscattering method. The dependence of the composition of deposited films of the target materials: Si, C, SiC and Fe, and the beam species and energies of Si - are reported.

Pulsed-laser deposition of selenium

The preparation and characterization of amorphous selenium thin films grown by pulsed-laser deposition (PLD) is presented. Two laser excitation regimes at 1064 and 532 nm were studied. Interesting relations between the surface quality and the different experimental parameters were found. High-purity thin films were produced with surface quality similar to that obtained by a thermal process. A study of the emission spectra of the plasma generated during ablation is included.

Ion-beam sputtering apparatus for deposition of multilayered films

Multilayered films are,composed of repeated alternate deposition of ultrathin layers of different materials. These films are of interest for their unique properties not intrisically found in conventional monolithic substances. Multilayered films have been prepared by several methods: molecular beam epitaxy [1], thermal evaporation [2, 3], chemical vapour deposition [4], and sputtering [5-7]. In an attempt to deposit thin films of tin oxide, we used an ion-beam sputtering (IBS) apparatus with a simplified accelerator system [8]. The IBS method is particularly attractive for deposition because a high-purity thin film with an improved adhesion to the substrate can be obtained. In the present letter we describe the construction of the IBS apparatus specially designed for the synthesis of multilayered films. The constructed apparatus is simple, relatively inexpensive and convenient to control. The results of analysing periodic structures of Pt/SnOx multilayers deposited by this apparatus are also presented. The outline of the apparatus used to prepare multilayered films is shown in Fig. 1. The vacuum chamber is a vertical cylinder, 40 cm in diameter and 80 cm tall, of which only the upper-half is actually used. The base pressure is below 1 x 10 5 torr. Argon gas of 99.9995% purity is fed into the ionsource chamber and the chamber pressure during the run is maintained at (1 + 0.1) x 10 4torr. The target is placed at about 45 ° to both the axis of the beam and the substrate. The distance from the centre of the target to the ion-source chamber and to the substrate is 3.5 and 5 cm, respectively. The target assembly can contain four different targets and the targets are screwed to the aluminium target-holders of 8-cm diameter. In this experiment two targets, platinum foils and a sintered tin oxide disc, were used. The rotation of the targets was carried out using an ordinary stepping motor (Oriental motor, PH266-01) in the vacuum chamber. Generally the vacuum hinders the rapid heat transfer, thus heat tends to accumulate in the running motor and augments its temperature. To avoid this temperature increase of the stepping motor, the motor is mounted on a water-cooled copper plate; flexible hoses are used to conduct the cooling water. Although the placing of the stepping motor in the vacuum chamber induces a possible contamination from the gaseous species from the organic materials in the motor, it makes the overall design of the apparatus very simple. A microcomputer (NEC, PC-8801) and a driver/controller (Cosmotron, PMC-14C) together with the stepping motor control the rotation of the targets. When the sputtering time to form a layer reaches a preset value, the control system turns the target assembly by 90 ° to the other target. It takes about 1 sec for this rotation. The substrate assembly contains eight different substrate holders that can be selected manually via a d.c. motor. The shutter has a window (2 c m x 4 cm) through which sputtered particles deposite on a designated substrate. During the pre-sputtering of the targets, the window is closed. The substrate-shutter separation is held at 4 mm so that all particles passing through the window hit the planned substrate, thus contamination of other substrates by the sputtered particles is avoided. The electrical connections for the system are shown schematically in Fig. 2. It is similar to that used in our previous experiment [8], however the stability of the discharge current increased markedly by employing a d.c. current supply (Metronix, 411A-32) and an insulation transformer instead of a voltage slider. The electrical system is run typically at a discharge voltage of 50 V, a discharge current of 600 mA, a beam voltage of 1000 V, an accelerator voltage of 150 V and an ionbeam current (defined here as the current between the target and the ground) of 0.8 mA. The temperatures of the substrate and the target reached 90 and 130°C, respectively after 3h; they were measured by a CA-thermocouple during the sputtering of an

High-purity thin films

High-purity thin films