This letter reports on a systematic investigation of sputter induced damage in graphene caused by low energy Ar+ ion bombardment. The integral numbers of ions per area (dose) as well as their energies are varied in the range of a few eV's up to 200 eV. The defects in the graphene are correlated to the dose/energy and different mechanisms for the defect formation are presented. The energetic bombardment associated with the conventional sputter deposition process is typically in the investigated energy range. However, during sputter deposition on graphene, the energetic particle bombardment potentially disrupts the crystallinity and consequently deteriorates its properties. One purpose with the present study is therefore to demonstrate the limits and possibilities with sputter deposition of thin films on graphene and to identify energy levels necessary to obtain defect free graphene during the sputter deposition process. Another purpose is to disclose the fundamental mechanisms responsible for defect formation in graphene for the studied energy range.
The deposition rate of reactively sputtered Al(2)O(3) coatings is demonstrated to increase by 80% upon tungsten doping of the used aluminium target. This effect is based on the recoil of the sputtering species at implanted dopants below the target surface and is termed sputter yield amplification. For the investigation of this effect, a novel type of magnetron sputter deposition system is employed that facilitates serial co-sputtering. In this technique doping of the elementary target is enabled by a dynamic sputtering process from an auxiliary cathode. In our case, the rotating aluminium target is dynamically coated with tungsten from this auxiliary cathode. Since the primary target rotates, the auxiliary cathode is placed in series with the primary erosion zone. The deposition rate of Al(2)O(3) can be considerably increased in this process already for very low concentrations of approximately 1% of tungsten in the resulting film. A characterization of the dynamics of reactive sputtering as a function of target rotation speed is performed.
Diamond deposition on healed Si-substrates was studied under microwave discharge generated by an electrode-antenna either in a ''point-to-plane'' arrangement or in a ''parallel-plane'' arrangement at gas pressures of 1-15 Torr in a mixture of hydrogen wit
Reactive sputtering is a widely used technique to deposit oxides, nitrides, etc. A serious drawback of this technique, however, is the drastic decrease in deposition rate that almost always occurs when depositing compound films as compared to depositing p
Several phenomena are neglected in the original “Berg model” in order to provide a simple model of the reactive sputtering process. There exist situations, however, where this simplified treatment limits the usefulness of the model. To partly correct for this, we introduce an upgraded version of the basic model. We abandon the simplifying assumption that compound targets are sputter eroded as molecules. Instead, the molecule is split and individual atoms will be sputter ejected. Also, the effect of ionized reactive gas atoms implanted into the target will be considered. We outline how to modify the original model to include these effects. Still, the mathematical treatment is maintained simple so that the new model may serve as an easy-to-understand tutorial of the complex mechanisms of reactive sputtering.
Multilayered structures with 14-50 nm periods composed of titanium and two different titanium oxides, TiO and TiO2, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO2/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO2 and rutile phase. DC electrical resistivity rho measured for temperatures ranging from 300 to 500 K exhibited a metallic-like behaviour (rho(473K) = 1.05 x 10(-5) to 1.45 x 10(-6) Omega m) with a temperature coefficient of resistance ranging from 1.20 x 10(-3) K-1 for the highest period (Lambda = 50.0 nm) down to negative values close to -4.97 x 10(-4) K-1 for the smallest one (Lambda = 14.0 nm). A relationship between the dimensions of periodic layers and their collective electrical resistivity is proposed where the resistivity does not solely depend on the total thickness of the film, but also depends on the chemical composition and thickness of each sub-layer. Charge carrier mobility and concentration measured by the Hall effect were both influenced by the dimension of TiO2/TiO/Ti periods and the density of ionized scattering centres connected to the titanium concentration in the metallic sub-layers.
A novel Zn-doped Al2O3 (ZAO) layer prepared by atomic layer deposition (ALD) is used as the charge storage medium in an In-Ga-Zn-O thin-film-transistor memory. The gate insulating stack of Al2O3/ZAO/Al2O3 is assembled in a single ALD step, and is found to possess a high electron storage capacity due to very deep defect levels. The memory device shows a threshold voltage shift as large as 6.38 V after a +15V/1 ms programming pulse, and quite good charge retention. Once programmed, the memory can be only light erased. The underlying mechanisms are discussed with the assistance of density functional theory calculations.
Semiconducting amorphous indium-gallium-zinc oxide (a-IGZO) films are integrated with an Al2O3/Pt-nanocrystals/ Al2O3 gate-stack to form UV-erasable thin-film transistor (TFT) memory. The threshold voltage (V-th), sub-threshold swing, I-ON/I-OFF ratio, and effective electron mobility of the fabricated devices are 2.1 V, 0.39 V/decade, similar to 10(6), and 8.4 cm(2)/V.s, respectively. A positive V-th shift of 2.25 V is achieved after 1-ms programming at 10 V-th, whereas a negative V-th shift as large as 3.48 V is attained after 5-s UV erasing. In addition, a 10-year memory window of 2.56 V is extrapolated at room temperature. This high-performance a-IGZO TFT memory is suitable for optical touch-panel applications.
Gas flow sputtering of Cu(In,Ga)Se-2 (CIGS) from two opposing Cu(In,Ga)Se-2 targets with slightly Cu-poor stoichiometry was performed, using i) selenium only provided by the target and ii) using additional selenium from an elemental source inside the sputtering system. In both cases the composition of the sputtered CIGS film was similar to the target. A sputter process without additional selenium supply led to poor cell results at about 2 % efficiency. After introducing a posttreatment in selenium atmosphere immediately after the sputter deposition, the cell results were dramatically improved to 12 %. With selenium added during the sputtering process, 13.7 % conversion efficiency was obtained without any post treatment. Gas flow sputtering uses a high gas flow to transport the material from the plasma to the growing film, thereby the atoms will be thermalized, similarly to in an evaporation process. Reactant gases can be supplied close to the substrate, outside the plasma, thereby reducing the risk for sputter damage.
With novel design and fabrication techniques, InGaZnO-based thin-film transistors with individual recessed back-gates were fabricated on flexible and transparent polymer substrates. The key components for the fabrication include using a machine park optimized for Si process technology, low-adhesion, room temperature parylene coating, AlOx–ZnOx(Al)-based inorganic lift-off process, and a recessed individual gate concept. Transistors were built to validate the viability of the design as well as aforementioned techniques. The demonstrated approach could open up new design possibilities for cheap, flexible devices, while the recessed-gate concept shows promise towards the use of more brittle layers in our flexible thin-film electronic devices.
Sputter deposited symmetric multilayers of (n Fe)/(n Ni), with individual thicknesses from n = 4 to n = 48 monolayers (ML), were deposited on epitaxial Cu/Si(001), and their microstructural evolution and magnetic properties versus n have been studied. Elemental layering can be seen with transmission electron microscopy down to n = 4 ML layer thickness, although an intermixed region characterized by a finite interface width is found to be present. This width is composed of the interface roughness as well as the interdiffusion between layers, but the relative contributions from these two sources could not be concluded by the techniques used. The measured elemental layering and X-ray reflectivity (XRR) give an upper limit to the interface width which must be smaller than the thinnest layers, 4 ML. Electron energy loss spectroscopy (EELS), depth profiling X-ray photoelectron spectroscopy (XPS) and also XRR reveal that Fe has a higher tendency to mix with Ni than vice versa. XPS does not have the resolution to measure this thin elemental layering: composition variations for n = 8 ML which are clearly seen by EELS are barely resolved by XPS. The structure was determined by X-ray diffraction, and an epitaxial fcc (001) structure is found to be maintained throughout the multilayers up to n less than or similar to 8 ML. For larger n values, relaxation starts by Fe-fcc(001) layers changing into Fe-bcc(110), which is then followed by Ni-fcc(001) changing from (001) to (111) orientation along the growth direction. A decreased total measured magnetic moment for the fully epitaxial multilayers can be explained by the fcc Fe layers being partly anti-ferromagnetic, whereas the relaxed multilayers exhibit the expected magnetic properties of (bcc Fe) +(fcc Ni).
This letter presents a proof-of-concept process for tunable, self-limiting growth of ultrathin epitaxial NiSi2 films on Si (100). The process starts with metal sputter-deposition, followed by wet etching and then silicidation. By ionizing a fraction of the sputtered Ni atoms and biasing the Si substrate, the amount of Ni atoms incorporated in the substrate after wet etching can be controlled. As a result, the thickness of the NiSi2 films is increased from 4.7 to 7.2 nm by changing the nominal substrate bias from 0 to 600 V. The NiSi2 films are characterized by a specific resistivity around 50 mu Omega cm.
We demonstrate the sputter-deposition of WS2 onto a single-layer graphene film leaving the latter disorder-free. The sputtering process normally causes defects to the graphene lattice and adversely affects its properties. Sputtering of WS2 yields significant amounts of energetic particles, specifically negative S ions, and reflected neutral Ar, and it is therefore used as a model system in this work. The disorder-free sputtering is achieved by increasing the sputteringpressure of Ar thereby shifting the kinetic energy distribution towards lower energies for the impinging particle flux at the substrate. Raman spectroscopy is used to assess the amount of damage to the graphene film. Monte Carlo simulations of the sputteringprocess show that W is completely thermalized already at relatively low sputtering pressure, whereas Ar and S need a comparably higher pressure to thermalize so as to keep the graphene film intact. Apart from becoming completely amorphous at 2.3 mTorr, the graphene filmremains essentially disorder-free when the pressure is increased to 60 mTorr. The approach used here is generally applicable and readily extendable to sputter-deposition of other material combinations onto sensitive substrates. Moreover, it can be used without changing the geometry of an existing sputtering setup.
It is well known that a compound layer may form at the target surface during reactive sputtering. However, the significance of this layer for the response to a change in target conditions has so far not been carefully investigated. The standard model for
We present a method using resonant nuclear reaction analysis combined with optical transmission and heavy-ion Rutherford backscattering spectrometry to study the absorption of hydrogen in single crystalline thin vanadium films. Probing with the resonant H-1(N-15,alpha gamma)C-12 reaction allows for highly resolved hydrogen depth profiling, while measurements along the crystal axes render possible the direct identification of the interstitial site occupancy. First experiments were performed on thin vanadium hydrides in Fe(Cr)/V superlattices revealing differences in site occupancy.
High power impulse magnetron sputtering (HiPIMS) has proven to be capable of substantial improvement of the quality of deposited coatings. Lately, there have been a number of reports indicating that the hysteresis effect may be reduced in HiPIMS mode resulting in an increase of the deposition rate of stoichiometric compound as compared to a direct current magnetron sputtering process in oxide mode. In this contribution, we have studied the hysteresis behaviour of Ti metal targets sputtered in Ar + O(2) mixtures. For fixed pulse on time and a constant average power, there is an optimum frequency minimizing the hysteresis. The effect of gas dynamics was analyzed by measurements of the gas refill time and rarefaction. Results indicate that the gas rarefaction may be responsible for the observed hysteresis behaviour. The results are in agreement with a previous study of Al oxide reactive process.
A systematic experimental study of reactive sputtering from substoichiometric targets of TiOx with x ranging from 0 to 1.75 is reported. Experimental results are compared with results from modeling. The developed model describes the observed behavior and explains the origins of the unexpectedly high deposition rate. The behavior is shown to originate from the presence of titanium suboxides at the target surface caused by preferential sputtering of the oxide. The model can be used for optimization of the target composition with respect to the deposition rate and film composition in a stable hysteresis-free reactive sputtering process.
Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiOx targets with different oxygen contents. The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films.
In this contribution, we summarize our work on increasing the deposition rate in reactive magnetron sputtering by sputtering yield amplification. Modelling of the sputtering process predicts that a very high deposition rate increase by more than 100 % may be achieved for oxides. Comparable values were measured experimentally using a setup suitable for up-scaling.
In sputtering yield amplification the target is doped with a heavy dopant in order to reflect the recoils created in a collision cascade towards the surface and thus increase the number of atoms sputtered from the surface. In order to realize the process, an experimental system for serial co-sputtering has been built and used for experimental studies. The dopants are introduced from an auxiliary cathode onto the primary rotating target and incorporated into the target surface by recoil implantation during sputtering. A necessary requirement for suitable doping elements is high atomic mass. Another important parameter is the surface binding energy as demonstrated by comparison of W and Bi, two heavy elements with very different surface binding energies. Using a dynamical model of the sputtering process, the performance of various doping elements is evaluated.
Reactive sputtering of Al and Ti targets with W and Bi doping was performed. The deposition rate of Al2O3 can be increased by 80 % by W doping of the Al target in very good agreement with predictions. For TiO2, however, an increase by more than 100 % was observed, substantially higher than predicted. Finally, the optical properties of W doped Al2O3 and TiO2 thin films are briefly discussed.
The main aim of this work is to present a way to estimate the values of surface binding energy for oxides. This is done by fitting results from the binary collisions approximation code Tridyn with data from the reactive sputtering processing curves, as well as the elemental composition obtained from x-ray photoelectron spectroscopy (XPS). Oxide targets of Al, Ti, V, Nb and Ta are studied. The obtained surface binding energies are then used to predict the partial sputtering yields. Anomalously high sputtering yield is observed for the TiO 2 target. This is attributed to the high sputtering yield of Ti lower oxides. Such an effect is not observed for the other studied metals. XPS measurement of the oxide targets confirms the formation of suboxides during ion bombardment as well as an oxygen deficient surface in the steady state. These effects are confirmed from the processing curves from the oxide targets showing an elevated sputtering rate in pure argon.
Many reactive sputter deposition applications require high deposition rates. The primary limiting parameters in magnetron sputtering are the target power dissipation and sputtering yields of the target elements. In reactive deposition of oxides, the deposition rate is of particular interest due to the low sputtering yield of most commonly used oxides. Traditional high rate techniques rely on a feedback control of the oxygen partial pressure to prevent formation of oxide on the target and hence enable operation in the transition area. An alternative approach, based on target doping, is presented in this paper.By doping the sputtering target with heavy elements, it is possible to substantially enhance the sputtering yield and hence the deposition rate. Simulations of the partial sputtering yield values for aluminium from doped targets sputtered in reactive atmosphere have been carried out. The Monte Carlo based TRIDYN computer code has been used for simulations. The program has been used to find out optimum alloying conditions to obtain maximum partial sputtering yield for deposition of Al2O3. Our simulations indicate that the sputtering yield amplification in reactive sputtering may lead to much higher relative deposition rate increase than in a nonreactive case. The highest relative increase may be achieved in the transition region but substantial increase is predicted also in the oxide mode.
Reactive sputtering is one of the most commonly employed processes for the deposition of thin films. However, the range of applications is limited by inherent instabilities, which necessitates the use of a complex feedback control of reactive gas (RG) partial pressure. Recently pulsing of the RG has been suggested as a possible alternative. In this report, the concept of periodically switching the RG flow between two different values is applied to the deposition of tungsten oxide. The trends in the measured time dependent RG pressure and discharge voltage are reproduced by a dynamical model developed for this process. Furthermore, the model predicts the compositional depth profile of the deposited film reasonably well, and in particular helps to understand the formation of the interfaces in the resulting multi-layer film.