Crystallization study by transmission electron microscopy of SrTiO3 thin films prepared by plasma-assisted ALD

The crystallization behavior of thin strontium titanate (SrTiO3, STO) films with ~15 nm thickness was studied by Transmission Electron Microscopy (TEM). Amorphous STO films with [Sr]/([Sr]+[Ti]) ratio ranging from 0.50 to 0.63 were deposited at 350°C by plasma-assisted ALD and subsequently treated by rapid thermal annealing in flowing N2 for crystallization. Different temperatures and annealing durations were employed to fully characterize the crystallization process. TEM analysis showed that transrotational crystals were formed and evidenced the influence of the STO composition and of the thermal budget applied on the grain size, crack and void formation. In particular, Sr-rich layers ([Sr]/([Sr]+[Ti] = 0.59) showed a finer crystalline structure which was imputed to a higher nucleation probability at the onset of the crystallization process. Crystallization into the perovskite structure was confirmed for all the film compositions studied. By tuning the STO composition and the thermal budget of the annealing step it was demonstrated that it is possible to control the microstructure of the crystallized film as a further step in optimizing the STO film properties

Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Vanadium(V) oxide supported on 7-A1203, GO2, Cr2O3, Si02, Ti02, and Zr02 was studied by X-ray fluorescence, by X-ray diffraction, and especially by the combination of Raman spectroscopy and temperature-programmed reduction (TPR) for qualitative and quantitative structural analysis, respectively. Catalysts were prepared via ion-exchange and wet-impregnation methods. The V contents ranged from - 1 to 40 wt % V. At low surface concentrations only surface vanadate phases of two-dimensional character are observed for all carriers. According to Raman and TPR data the structure of these surface vanadate species is independent of the preparation technique. At medium and high surface concentrations, the webimpregnated samples already contain crystalline V20b At equal surface concentrations the ion-exchanged catalysts contain no V205 crystallites. An exception is Si02 on which also crystalline V206 is formed in both preparation techniques. Monolayer stability toward thermal treatment decreases in the order AZO>3 Ti02> Ce02,w hereas on heating ion-exchanged V/Si02 the crystalline V206 spreads out over the silica surface. The reducibilities of the ion-exchanged catalyats, as measured by TPR, can be used as a measure for the contact interaction between vanadia and the carrier oxides. At temperatures of 500-800 K, this interaction ranges from strong with titania to weak with silica as a carrier

Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices

Atmospheric pressure spatial atomic layer deposition (AP-SALD) has recently emerged as an appealing technique for rapidly producing high quality oxides. Here, we focus on the use of AP-SALD to deposit functional ZnO thin films, particularly on the reactors used, the film properties, and the dopants that have been studied. We highlight how these films are advantageous for the performance of solar cells, organometal halide perovskite light emitting diodes, and thin-film transistors. Future AP-SALD technology will enable the commercial processing of thin films over large areas on a sheet-to-sheet and roll-to-roll basis, with new reactor designs emerging for flexible plastic and paper electronics.The authors acknowledge the support of the Rutherford Foundation of New Zealand and the Cambridge Commonwealth, European and International Trusts, and the ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276. DMR acknowledges Marie Curie Actions (FP7/2007-2013, Grant Agreement Nos. 219332 and 631111), and the Ramon y Cajal 2011 programme from the Spanish MICINN and the European Social Fund, and the Comissionat per a Universitats I Recerca (CUR) del DIUE de la Generalitat de Catalunya, Spain.This is the final published version of the article. It was originally published in APL Materials (Hoye RLZ, Muñoz-Rojas D, Nelson SF, Illiberi A, Poodt P, Roozeboom F, MacManus-Driscoll JL, APL Materials, 2015, 3, 040701, doi:10.1063/1.4916525). The final version is available at http://dx.doi.org/10.1063/1.491652

Thermal and Remote Plasma ALD of Ru from CpRu(CO)2Et and O2

Ruthenium (Ru) is regarded as an electrode candidate on ultrahigh-k SrTiO3 dielectric films for future high-density trench capacitors. To achieve conformal film growth, atomic layer deposition (ALD) of Ru is investigated. To this end, the use of an oxidizing reactant is desired to avoid electronic degradation of the interface properties of SrTiO3 as found when using a NH3 plasma for Ru ALD or when using thermal ALD TiN as electrode. Thermal ALD of Ru using O2 gas, however, generally results in a pronounced nucleation delay and high surface roughness. The current work aims at developing ALD of Ru using an O2 plasma in order to improve the film nucleation and to try to obtain smoother films. Using the novel CpRu(CO)2Et precursor and O2, both thermal and remote plasma ALD of Ru were studied in the same reactor at wafers up to 200 mm. Unlike thermal ALD, the Ru film growth by remote plasma ALD does not rely on the dissociative chemisorption of O2 on the Ru surface and good film nucleation is expected by providing O radicals from the gas phase. In situ spectroscopic ellipsometry, x-ray reflectometry and diffractometry, and electrical measurements clearly show this benefit of the O2 plasma. The Ru films almost immediately nucleate for the plasma-based process, whereas the thermal process showed a nucleation delay of approximately 100 cycles. Once the film growth has started, the growth per cycle (1 Å/cycle), the electrical properties (20 µOcm for >5 nm films), and the polycrystalline structure are similar for both ALD processes. However, despite the drastically improved nucleation, the remote plasma ALD Ru films show higher roughness values than the thermal ALD Ru films (roughness of 13 nm and 8 nm for 20 nm thick films, respectively). To elucidate this unexpected phenomenon, the film nucleation and surface reactions were examined. Mass spectrometry provided insight into the reaction products (CO, CO2 and H2O mainly) and, therefore, into the surface chemistry ruling both ALD processes. Optical emission spectroscopy delivered information on the species created during plasma exposure. A reaction mechanism will be proposed for these oxygen-based ALD Ru processes that accounts not only for the differences in nucleation, but also relates to the roughness development of the Ru films

Atmospheric-pressure atomic layer deposition:recent applications and new emerging applications in high-porosity/3D materials

Atomic layer deposition (ALD) is a widely recognized technique for depositing ultrathin conformal films with excellent thickness control at Ångström or (sub)monolayer level. Atmospheric-pressure ALD is an upcoming ALD process with a potentially lower ownership cost of the reactor. In this review, we provide a comprehensive overview of the recent applications and development of ALD approaches emphasizing those based on operation at atmospheric pressure. Each application determines its own specific reactor design. Spatial ALD (s-ALD) has been recently introduced for the commercial production of large-area 2D displays, the surface passivation and encapsulation of solar cells and organic light-emitting diode (OLED) displays. Atmospheric temporal ALD (t-ALD) has opened up new emerging applications such as high-porosity particle coatings, functionalization of capillary columns for gas chromatography, and membrane modification in water treatment and gas purification. The challenges and opportunities for highly conformal coating on porous substrates by atmospheric ALD have been identified. We discuss in particular the pros and cons of both s-ALD and t-ALD in combination with their reactor designs in relation to the coating of 3D and high-porosity materials.</p

Surface passivation of silicon solar cells using industrially relevant Al2O3 deposition techniques

The next generation of industrial silicon solar cells aims at efficiencies of 20% and above. To achieve this goal using ever-thinner silicon wafers, a highly effective surface passivation of the cell front and rear is required. In the past, finding a suitable dielectric layer providing a high-quality rear passivation has been a major challenge. Aluminium oxide (Al2O3) grown by atomic layer deposition (ALD) has only recently turned out to be a nearly perfect candidate for such a dielectric. However, conventional ALD is limited to deposition rates well below 2nm/min, which is incompatible with industrial solar cell production. This paper assesses the passivation quality provided by three different industrially relevant techniques for the deposition of Al2O3 layers, namely high-rate spatial ALD, plasma-enhanced chemical vapour deposition (PECVD) and reactive sputtering