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  • Sharma, Varun; Natarajan, Suresh Kondati; Elliott, Simon D.; Blomberg, Tom; Haukka, Suvi; Givens, Michael E.; Tuominen, Marko; Ritala, Mikko (2021)
    Thermally activated chemical vapor-phase etching of titanium nitride (TiN) is studied by utilizing either alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4) or by using CCl4 alone. Nitrogen (N-2) gas purge steps are carried out in between every reactant exposure. Titanium nitride is etched in a non-self-limiting way by NbF5-CCl4 based binary chemistry or by CCl4 at temperatures between 370 and 460 degrees C. Spectroscopic ellipsometry and a weight balance are used to calculate the etch per cycle. For the binary chemistry, an etch per cycle of approximate to 0.8 angstrom is obtained for 0.5 and 3 s long exposures of NbF5 and CCl4, respectively at 460 degrees C. On the contrary, under the same conditions, the etch process with CCl4 alone gives an etch per cycle of about 0.5 angstrom. In the CCl4-only etch process, the thickness of TiN films removed at 460 degrees C varies linearly with the number of etch cycles. Furthermore, CCl4 alone is able to etch TiN selectively over other materials such as Al2O3, SiO2, and Si3N4. X-ray photoelectron spectroscopy and bright field transmission electron microscopy are used for studying the post-etch surfaces. To understand possible reaction products and energetics, first-principles calculations are carried out with density functional theory. From thermochemical analysis of possible reaction models, it is found that NbF5 alone cannot etch TiN while CCl4 alone can etch it at high temperatures. The predicted byproducts of the reaction between the CCl4 gas molecules and TiN surface are TiCl3 and ClCN. Similarly, TiF4, NbFCl3, and ClCN are predicted to be the likely products when TiN is exposed to both NbF5 and CCl4. A more favorable etch reaction is predicted when TiN is exposed to both NbF5 and CCl4 (Delta G = -2.7 eV at 640 K) as compared to exposure to CCl4 only (Delta G = -2 eV at 640 K) process. This indicates that an enhanced etch rate is possible when TiN is exposed alternately to both NbF5 and CCl4, which is in close agreement with the experimental results.
  • Rontu, Ville; Nolvi, Anton; Hokkanen, Ari; Haeggström, Edward; Kassamakov, Ivan; Franssila, Sami (2018)
    We have investigated elastic and fracture properties of amorphous Al2O3 thin films deposited by atomic layer deposition (ALD) with bulge test technique using a free-standing thin film membrane and extended applicability of bulge test technique. Elastic modulus was determined to be 115 GPa for a 50 nm thick film and 170 GPa for a 15 nm thick film. Residual stress was 142 MPa in the 50 nm Al2O3 film while it was 116 MPa in the 15 nm Al2O3 film. Density was 3.11 g cm(-3) for the 50 nm film and 3.28 g cm(-3) for the 15 nm film. Fracture strength at 100 hPa s(-1) pressure ramp rate was 1.72 GPa for the 50 nm film while for the 15 nm film it was 4.21 GPa, almost 2.5-fold. Fracture strength was observed to be positively strain-rate dependent. Weibull moduli of these films were very high being around 50. The effective volume of a circular film in bulge test was determined from a FEM model enabling future comparison of fracture strength data between different techniques.
  • Wlodarski, Maksymilian; Putkonen, Matti; Norek, Malgorzata (2020)
    Infrared (IR) spectroscopy is a powerful technique to characterize the chemical structure and dynamics of various types of samples. However, the signal-to-noise-ratio drops rapidly when the sample thickness gets much smaller than penetration depth, which is proportional to wavelength. This poses serious problems in analysis of thin films. In this work, an approach is demonstrated to overcome these problems. It is shown that a standard IR spectroscopy can be successfully employed to study the structure and composition of films as thin as 20 nm, when the layers were grown on porous substrates with a well-developed surface area. In contrast to IR spectra of the films deposited on flat Si substrates, the IR spectra of the same films but deposited on porous ceramic support show distinct bands that enabled reliable chemical analysis. The analysis of Zn-S ultrathin films synthesized by atomic layer deposition (ALD) from diethylzinc (DEZ) and 1,5-pentanedithiol (PDT) as precursors of Zn and S, respectively, served as proof of concept. However, the approach presented in this study can be applied to analysis of any ultrathin film deposited on target substrate and simultaneously on porous support, where the latter sample would be a reference sample dedicated for IR analysis of this film.
  • Honkanen, Ari-Pekka; Ollikkala, Sami; Ahopelto, Taru; Kallio, Antti-Jussi; Blomberg, Merja; Huotari, Simo (2019)
    We present a low-cost laboratory X-ray absorption spectrometer that uses a conventional X-ray tube source and bent Johann-type crystal monochromators. The instrument is designed for X-ray absorption spectroscopy studies in the 4-20 keV range which covers most K edges of 3d transition metals and L edges of 5d transition metals and actinides. The energy resolution is typically in the range of 1-5 eV at 10 keV depending on the crystal analyser and the Bragg angle. Measurements can be performed in transmission, fluorescence, and imaging modes. Due to its simple and modular design, the spectrometer can be modified to accommodate additional equipment and complex sample environments required for in situ studies. A showcase of various applications is presented. Published under license by AIP Publishing.
  • Mattinen, Miika; King, Peter J.; Khriachtchev, Leonid; Meinander, Kristoffer; Gibbon, James T.; Dhanak, Vin R.; Räisänen, Jyrki; Ritala, Mikko; Leskelä, Markku (2018)
    Semiconducting 2D materials, such as SnS2, hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 degrees C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.
  • Donsberg, Timo; Manoocheri, Farshid; Sildoja, Meelis; Juntunen, Mikko; Savin, Hele; Tuovinen, Esa; Ronkainen, Hannu; Prunnila, Mika; Merimaa, Mikko; Tang, Chi Kwong; Gran, Jarle; Mueller, Ingmar; Werner, Lutz; Rougie, Bernard; Pons, Alicia; Smid, Marek; Gal, Peter; Lolli, Lapo; Brida, Giorgio; Rastello, Maria Luisa; Ikonen, Erkki (2017)
    The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.
  • Srur-Lavi, Onit; Miikkulainen, Ville; Markovsky, Boris; Grinblat, Judith; Talianker, Michael; Fleger, Yafit; Cohen-Taguri, Gili; Mor, Albert; Tal-Yosef, Yosef; Aurbach, Doron (2017)
    In this paper, we studied the influence of LiAlO2 coatings of 0.5, 1 and 2 nm thickness prepared by Atomic Layer Deposition onto LiNi0.8Co0.15Al0.05O2 electrodes, on their electrochemical behavior at 30 and 60 degrees C. It was demonstrated that upon cycling, 2 nm LiAlO2 coated electrodes displayed similar to 3 times lower capacity fading and lower voltage hysteresis comparing to bare electrodes. We established a correlation among the thickness of the LiAlO2 coating and parameters of the self-discharge processes at 30 and 60 degrees C. Significant results on the elevated temperature cycling and aging of bare and LiAlO2 coated electrodes at 4.3 V were obtained and analyzed for the first time. By analyzing of X-ray diffraction patterns of bare and 2 nm coated LiNi0.8Co0.15Al0.05O2 electrodes after cycling, we concluded that cycled materials preserved their original structure described by R-3m space group and no additional phases were detected. (c) The Author(s) 2017. Published by ECS. All rights reserved.
  • Mirhashemihaghighi, Shadi; Swiatowska, Jolanta; Maurice, Vincent; Seyeux, Antoine; Klein, Lorena H.; Salmi, Emma; Ritala, Mikko; Marcus, Philippe (2016)
    Surface smoothening by substrate annealing was studied as a pre-treatment for improving the corrosion protection provided to copper by 10, 20 and 50 nm thick alumina coatings deposited by atomic layer deposition. The interplay between substrate surface state and deposited film thickness for controlling the corrosion protection provided by ultrathin barrier films is demonstrated. Pre-annealing at 750 degrees C heals out the dispersed surface heterogeneities left by electropolishing and reduces the surface roughness to less than 2 nm independently of the deposited film thickness. For 10 nm coatings, substrate surface smoothening promotes the corrosion resistance. However, for 20 and 50 nm coatings, it is detrimental to the corrosion protection due to local detachment of the deposited films. The weaker adherence of the thicker coatings is assigned to the stresses accumulated in the films with increasing deposited thickness. Healing out the local heterogeneities on the substrate surface diminishes the interfacial strength that is bearing the stresses of the deposited films, thereby increasing adhesion failure for the thicker films. Pitting corrosion occurs at the local sites of adhesion failure. Intergranular corrosion occurs at the initially well coated substrate grain boundaries because of the growth of a more defective and permeable coating at grain boundaries. (C) 2016 Elsevier B.V. All rights reserved.
  • Sharma, Varun; Blomberg, Tom; Haukka, Suvi; Cembella, Shaun; Givens, Michael E.; Tuominen, Marko; Odedra, Rajesh; Graff, Wes; Ritala, Mikko (2021)
    In this work, thermal based gas-phase etching of titanium nitride (TiN) is demonstrated using thionyl chloride (SOCl2) as a novel etchant. A single etchant is utilised in a pulsed fashion to etch TiN. This type of etching technique may also be considered as a chemical gas-phase or dry etching. The removed TiN amount was measured by various techniques like spectroscopic ellipsometry (SE), weighing balance and in some cases X-ray reflectometry (XRR). Additionally, the post-etch surfaces were analysed with X-ray photoelectron spectroscopy (XPS) and bright field transmission electron microscopy (BF-TEM). The surface roughness and morphology of before and after etching TiN films were measured using atomic force microscopy (AFM). The etch per cycle (EPC) was calculated and is plotted as a function of SOCl2 pulse time, purge time after SOCl2 exposure, number of etch cycles and etch temperature (T-etch). An increase in EPC with an increase in SOCl2 pulse time as well as etch temperature was observed. SOCl2 is able to etch TiN starting from 270 degrees C with an EPC of about 0.03 angstrom to almost 1.2 angstrom at 370 degrees C. Arrhenius plot determined the activation energy (E-a) of about 25 kcal/mol for TiN etching by SOCl2. In addition, the etch selectivity between different substrates such as silicon dioxide (SiO2), silicon nitride (Si3N4) and aluminum oxide (Al2O3) was investigated on blanket as well as 3D structures. Moreover, thermodynamic calculations were performed for various possible etch reactions. Titanium from TiN is proposed to be etched in the form of either titanium trichloride (TiCl3) or titanium tetrachloride (TiCl4). Nitrogen from TiN films may form volatile by-products such as diatomic nitrogen (N-2), nitrous oxide (N2O) and nitrogen dioxide (NO2).
  • Lovikka, Ville Antero; Airola, Konsta Petteri; McGuinness, Emily; Zhang, Chao; Vehkamäki, Marko; Kemell, Marianna; Losego, Mark; Ritala, Mikko; Leskelä, Markku (2022)
    Selective deposition of hybrid and inorganic materials inside nanostructures could enable major nanotechnological advances. However, inserting ready-made composites inside nanocavities may be difficult, and therefore, stepwise approaches are needed. In this paper, a poly(ethyl acrylate) template is grown selectively inside cavities via condensation-controlled toposelective vapor deposition, and the polymer is then hybridized by alumina, titania, or zinc oxide. The hybridization is carried out by infiltrating the polymer with a vapor-phase metalorganic precursor and water vapor either via a short-pulse (atomic layer deposition, ALD) or a long-pulse (vapor phase infiltration, VPI) sequence. When the polymer-MOx hybrid material is calcined at 450 degrees C in air, an inorganic phase is left as the residue. Various suspected confinement effects are discussed. The infiltration of inorganic materials is reduced in deeper layers of the cavity-grown polymer and is dependent on the cavity geometry. The structure of the inorganic deposition after calcination varies from scattered particles and their aggregates to cavity-capping films or cavity-filling low-density porous deposition, and the inorganic deposition is often anisotropically cracked. A large part of the infiltration is achieved already during the short-pulse experiments with a commercial ALD reactor. Furthermore, the infiltrated polymer is more resistant to dissolution in acetone whereas the inorganic component can still be heavily affected by phosphoric acid.
  • Kestilä, Antti; Nordling, Kalle Gustaf Martinpoika; Miikkulainen, Ville; Kaipio, Mikko; Tikka, Tuomas; Salmi, Mika; Auer, Aleksi; Leskelä, Markku; Ritala, Mikko (2018)
    Abstract Space technology has been an early adopter of additive manufacturing (AM) as a way of quickly producing relatively complex systems and components that would otherwise require expensive and custom design and production. Space as an environment and long-term survivability pose challenges to materials used in AM and these challenges need to be addressed. Atomic layer deposition (ALD) is an effective coating method enabling conformal and precise coating of the complete AM print. This work analyses how an ALD coating of aluminium oxide on acrylonitrile butadiene styrene (ABS) and polyamide PA 2200 plastic AM prints benefits and protects them. This was studied in the context of in-space propulsion fluidics, where propellant flow properties also matter. AM was performed with material extrusion and selective laser sintering methods that are commonly used. Tests were performed with a simple bang-bang controller test setup and a mass spectrometer, and the existence of the coating was confirmed with scanning electron microscope imaging.
  • Ahaliabadeh, Zahra; Miikkulainen, Ville; Mäntymäki, Miia; Mousavihashemi, Seyedabolfazl; Lahtinen, Jouko; Lide, Yao; Jiang, Hua; Mizohata, Kenichiro; Kankaanpää, Timo; Kallio, Tanja (2021)
    Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (
  • Holler, M.; Diaz, A.; Guizar-Sicairos, M.; Karvinen, P.; Färm, Elina; Härkönen, Emma; Ritala, Mikko; Menzel, A.; Raabe, J.; Bunk, O. (2014)