Elastic and fracture properties of free-standing amorphous ALD Al2O3 thin films measured with bulge test

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.Peer reviewe

Atomikerroskasvatus mikro- ja nanoteknologiassa

Atomic layer deposition (ALD) has become a widely used thin film deposition method in fabrication of many micro- and nanodevices. In this thesis, the reasons for this are investigated by studying what ALD has enabled for the applications based on available literature. In addition to reviewing existing applications, ALD was used in selected experimental case studies to enable better performing thin films and/or new improved device designs. Based on the literature review the most important advantages that ALD offers are conformal deposition and precise thickness control combined with relatively low deposition temperatures. As the device dimensions and required film thicknesses have decreased, and the devices have turned from planar to three-dimensional, ALD has gained more momentum. However, due to the the biggest downside of ALD, slow deposition rate, ALD is selected as the depositon method only when other deposition methods fail to meet the requirements. In the first experimental case, AlN deposition was studied from less used AlCl3 precursor with aim of depositing pure and crystalline AlN thin films. The AlN deposition from AlCl3 showed promise and enabled deposition of relatively pure AlN films. However, more work is still needed in order to determine whether it is a better precursor option for the deposition than the more commonly employed AlMe3. Additionally, the possibility to control residual stress of the AlN film was observed. In the second experimental case, ALD was used to deposit heterogenous catalyst into microreactors. ALD enabled deposition of even distribution of Pt nanoparticles in microreactor walls with controllable size, which showed high activity in hydrogenation of propene.In the third experimental case, ALD Al2O3 and AlN was studied as thin free-standing membranes. The thin ALD Al2O3 membranes showed exceptional mechanical properties. Membranes of 400-µm diameter were fabricated as thin as 15 nm. The amorphous Al2O3 membranes were found more durable than polycrystalline AlN membranes. In the final experimental case, ALD was used to enable new designs for fabrication of superomniphobic surfaces. Superomniphobic surfaces that could repel all room temperature liquids were realized with the help of ALD SiO2. Role of ALD in the fabrication of the superomniphobic surfaces could increase if the dimensions of the surface features are shrunk further. This could also enable decreasing the temperature budget of the process to <120 °C.Atomikerroskasvatuksesta (ALD) on tullut laajasti käytetty ohutkalvonkasvatusmenetelmä mikro- ja nanoteknologiassa. Tämän työn kirjallisuusosassa on käyty läpi syitä, joiden johdosta ALDn suosio on kasvanut. Kokeellisessa osassa tarkastellaan ALD-kalvojen uusia sovelluskohteita, ja tutkitaan ALD-prosesseja erityisesti sovellusten vaatimusnäkökohdista käsin, tavoitteena laadukkaammat ohutkalvot ja/tai kokonaan uudenlaiset laiterakenteet. ALDn merkittävimmät edut ovat konformaalinen pinnoitus ja tarkka paksuuskontrolli yhdistettyinä mataliin kasvatuslämpötiloihin. Mikro- ja nanoteknologian komponenttien koon pienentyminen ja komponenttien muuttumien kolmiulotteisiksi on lisännyt tarvetta ALDlle. ALDn suurin heikkous, hidas kasvunopeus, kuitenkin aiheuttaa sen, että menetelmä on usein kilpailukykyinen muihin pinnoitusmenetelmiin verrattuna vain, jos nämä muut menetelmät eivät kykene täyttämään asetettuja vaatimuksia. Ensimmäisessä osatutkimuksessa selvitettiin puhtaan ja hyvän kidelaadun omaavan AlN:n kasvatusta harvemmin tutkitusta AlCl3-lähtöaineesta. AlN:n kasvatus AlCl3:sta oli lupaavaa ja sen avulla saatiin kasvatettua suhteellisen puhtaita ohutkalvoja. Lisäksi havaittiin mahdollisuus kontrolloida AlN-ohutkalvon jännityksiä. Toisessa osatutkimuksessa ALDtä käytettiin heterogeenisen katalyytin kasvattamiseen mikroreaktoreihin. ALD mahdollisti Pt-nanopartikkelien tasaisen jakautumisen mikroreaktoreiden pinnoille, ja nanopartikkelien koon kontrolloimisen. ALD-Pt-nanopartikkeleilla havaittiin olevan korkea aktiviteetti propeenin hydrauksessa propaaniksi. Kolmannessa osatutkimuksessa tutkittiin ALD Al2O3:n ja AlN:n soveltuvuutta itsekantaviksi kalvoiksi. ALD Al2O3 kalvoilla oli erinomaiset mekaaniset ominaisuudet, minkä johdosta pystyttiin valmistamaan jopa vain 15 nm paksuisia ja halkaisijaltaan 400 µm olevia itsekantavia kalvoja. Nämä amorfiset Al2O3-kalvot osoittautuivat kestävyydeltään paremmiksi kuin monikiteiset AlN-kalvot. Viimeisessä osatutkimuksessa ALDtä käytettiin mahdollistamaan uudenlaisten superomnifobisten pintojen valmistaminen. Nämä superomnifobiset pinnat kykenivät hylkimään kaikkia tunnettuja nesteitä huoneenlämpötilassa. ALDn rooli näiden pintojen valmistamisessa saattaa kasvaa tulevaisuudessa, mikäli rakenteiden dimensioita pienennetään edelleen. Tämä mahdollistaisi pinnoille korkeamman painetoleranssin. ALDn käyttö mahdollistaisi myös koko prosessin maksimilämpötilan laskemisen jopa alle 120 °C:n

NbN ohutkalvojen kasvatus atomikerroskasvatusmenetelmällä

Niobium nitride thin films have been usually deposited by reactive magnetron sputtering. Atomic layer deposition (ALD) has emerged as viable candidate for growth of ultrathin films. Its benefits include conformal deposition and nanometer scale thickness control. So far deposition of cubic NbN phase has been realized by ALD from NbCl5 and NH3 only with help of zinc as an additional reducing agent or by PEALD from organometallic precursors. In this work we developed deposition processes for recently acquired ALD tool aiming for deposition of NbN from NbCl5 without zinc. We deposited NbNx thin films from NbCl5 using NH3, H2 and NH3 as separate pulses; NH3-plasma; H2/N2-plasma with varying flow rate ratios; and H2-plasma. PEALD depositions in this work are the first published PEALD processes for NbN using NbCl5 as a precursor. Thermally deposited films using NH3 had resistivity of 650 μΩcm at best and growth rate varied from 0.34–0.52 Å/cycle. Resistivity is slightly higher than the best, 550–600 μΩcm, reported for similar process. Also GPC is higher than typically reported 0.25 Å/cycle. Films were clean having less than 1 at% impurities for films grown at 500°C. Cl-content increased from 0.3 at% to 1.8 at% as deposition temperature decreased from 500°C to 400°C. Nb/N ratios in the films were close to 0.8. Films grown with plasma typically exhibited even higher GPC, 0.5–0.85 Å/cycle. Exception to this was film grown on top of amorphous AlN which had growth rate of 0.35 Å/cycle. The best resistivity obtained for plasma processes was 490 μΩcm. ToF-ERDA measurements from H2-plasma grown film revealed incorporation of nitrogen into the film from carrier gas lines. None of the grown films exhibited superconductivity. It was determined that NH3 has insufficient reducing power to create stoichiometric NbN and that use of H2 to replace zinc as additional reducing agent would require higher temperatures. Deposition of superconductive NbN films should be possible with plasma-enhancement after changes to the ALD equipment is made in order to fully operate under argon atmosphere.Niobiumnitridi ohutkalvoja on tavallisesti kasvatettu reaktiivisella magnetronisputteroinnilla. Atomikerroskasvatusmenetelmästä (Atomic layer deposition, ALD) on tullut varteenotettava kandidaatti erittäin ohuiden ohutkalvojen kasvatukseen. Sen etuina on muunmuassa konformaalinen kasvu ja mahdollisuus paksuuden kontrolloimiseen nanometrin mittaluokassa. Tähän asti kiderakenteeltaan kuutiollisia NbN ohutkalvoja on saatu kasvatettua ALD:llä NbCl5:stä ja ammoniakista ainoastaan käyttämällä sinkkiä lisäpelkistimenä lähtöainepulssien välissä. Tämän työn tavoitteena on kehittää NbN ohutkalvojen kasvatusprosessi uudelle ALD-laitteelle käyttäen NbCl5:a ilman sinkkiä. Kasvatimme NbNx-ohutkalvoja NbCl5:sta käyttäen muina lähtöaineina ammoniakkia; vetyä ja ammoniakkia erillisinä pulsseina; ammoniakkiplasmaa; typpi-vety-plasmaa vaihtelevalla typen ja vedyn virtaus suhteilla; ja vety-plasmaa. Tässä työssä tehdyt PEALD NbN prosessit ovat ensimmäiset PEALD NbN prosessit, joissa on käytetty NbCl5 lähtöaineena. Ohutkalvoilla, jotka kasvatettiin käyttäen ammoniakkia, paras havaittu resistiivisyys oli 650 μΩcm ja kasvunopeus vaihteli 0,34 ja 0,52 Å/sykli välillä. Havaittu resistiivisyys on hieman suurempi kuin kirjallisuudessa havaittu resistiivisyys vastaavalle prosessille joka on 550–600 μΩcm. Samoin kasvunopeus on suurempi kuin kirjallisuudessa havaittu 0.25 Å/sykli. Kalvot olivat erittäin puhtaita. 500 °C kasvatetuissa kalvoissa alle 1 at% epäpuhtauksia. Kloorin määrä kalvoissa havaittiin riippuvan kasvatuslämpötilasta. Klooripitoisuus 400 °C kasvatetuissa kalvoissa oli 1.8 at% ja se laski 0.3 at%:in, kun kasvatuslämpötila nostettiin 500°C:een. Niobiumin suhde typpeen kalvoissa oli noin 0.8. Plasman kanssa kasvatetuilla kalvoilla oli tyypillisesti korkeampi kasvunopeus. Havaittu kasvunopeus oli noin 0,5–0,85 Å/sykli. Poikkeus tähän oli kalvo, joka kasvatettiin AlN:n päälle, jonka kasvunopeus oli 0,35 Å/sykli. Paras resistiivisyys, joka plasman avulla saavutettiin oli 490 μΩcm. ToF-ERDA mittausten perusteella vety-plasmalla kasvatetuissa kalvoissa oli typpeä, jonka lähteeksi todettiin kantajakaasu. Yksikään kasvatetuista kalvoista ei ollut suprajohtava. Lopputuloksena päädyttiin siihen, että ammoniakin pelkistyskyky ei ole riittävä, jotta pystyttäisiin kasvattamaan stoikiometrista NbN:ä. Lisäksi todettiin, että vedyn käyttö lisäpelkistimenä, samaan tapaan kuin sinkkiä on käytetty, vaatisi korkeammat lämpötilat toimiakseen. Suprajohtavien kalvojen kasvatuksen pitäisi olla mahdollista plasman avulla, kunhan ALD-laitteseeen saadaan tehtyä muutos, jotta kaikki kantajakaasut olisivat argonia

Scalable Superomniphobic Surfaces

Superomniphobic surfaces that repel liquids of extremely low surface tension rely on carefully fabricated doubly re-entrant topographies, typically made by silicon deep reactive ion etching technology. However, previously published processes have depended on critically timed etching steps, which are difficult to downscale. We present a scalable process that eliminates the critically timed etching steps. It is based on the use of silicon-on-insulator wafers and a silicon oxide foot of the micropillar, which makes the isotropic silicon release step non-critical. The process allows easy downscaling of pillars from 20 μm to 10 μm and 5μm. The downscaling increases the stability of the Cassie state. Based on the process, we are able to create superomniphobic surfaces that sustain perfluorohexane (FC-72), which has the lowest surface tension of the known liquids at room temperature ( γ lv=11.91 mN/m at 20 °C), in the Cassie state at droplet diameters down to 200 micrometers. These are the smallest perfluorohexane droplets repelled to date. [2019-0207].Peer reviewe

Mechanical properties and reliability of aluminum nitride thin films

Knowledge of the mechanical properties and fatigue behavior of thin films is important for the design and reliability of microfabricated devices. This study uses the bulge test to measure the residual stress, Young's modulus, and fracture strength of aluminum nitride (AlN) thin films with different micro-structures prepared by sputtering, metalorganic vapor phase epitaxy (MOVPE), and atomic layer deposition (ALD). In addition, the fatigue behavior is studied under cyclic loading. The results indicate that the fracture strength and Young's modulus of AlN are mainly determined by the film microstructure, which is consecutively influenced by the deposition method and conditions. A microstructure with a higher order of crystallinity has increased fracture strength and Young's modulus. Additionally, the strength limiting defects are located at the film-substrate interface. The measured residual stresses were 249, 876, 1,526, and 272 MPa for two sputtered films of different thicknesses, MOVPE and ALD films, respectively. The fracture strengths were 1.42, 1.54, 2.76, and 0.61 GPa, and Young's moduli were 335, 343, 346, and 272 GPa. No clear signs of fatigue were observed after 10,000 cycles at a load corresponding to 83% of the fracture strength. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe

Efficient Catalytic Microreactors with Atomic-Layer-Deposited Platinum Nanoparticles on Oxide Support

Microreactors attract a significant interest for chemical synthesis due to the benefits of small scales such as high surface to volume ratio, rapid thermal ramping, and well-understood laminar flows. The suitability of atomic layer deposition for application of both the nanoparticle catalyst and the support material on the surfaces of channels of microfabricated silicon microreactors is demonstrated in this research. Continuous-flow hydrogenation of propene into propane at low temperatures with TiO2-supported catalytic Pt nanoparticles was used as a model reaction. Reaction yield and mass transport were monitored by high-sensitivity microcoil NMR spectroscopy as well as time-of-flight remote detection NMR imaging. The microreactors were shown to be very efficient in propene conversion into propane. The yield of 100 % was achieved at 508 C with a reactor decorated with Pt nanoparticles of average size of roughly 1 nm and surface coverage of 3.2 % in 20 mm long reaction channels with a residence time of 1100ms. The activity of the Pt catalyst surfaces was on the order of several to tens of mmol s-1m-2.Peer reviewe

Atomic layer deposition of AlN from AlCl3 using NH3 and Ar/NH3 plasma

The atomic layer deposition (ALD) of AlN from AlCl3 was investigated using a thermal process with NH3 and a plasma-enhanced (PE)ALD process with Ar/NH3 plasma. The growth was limited in the thermal process by the low reactivity of NH3, and impractically long pulses were required to reach saturation. Despite the plasma activation, the growth per cycle in the PEALD process was lower than that in the thermal process (0.4 Å vs 0.7 Å). However, the plasma process resulted in a lower concentration of impurities in the films compared to the thermal process. Both the thermal and plasma processes yielded crystalline films; however, the degree of crystallinity was higher in the plasma process. The films had a preferential orientation of the hexagonal AlN [002] direction normal to the silicon (100) wafer surface. With the plasma process, film stress control was possible and tensile, compressive, or zero stress films were obtained by simply adjusting the plasma time.peerReviewe

Efficient catalytic microreactors with atomic-layer-deposited platinum nanoparticles on oxide support

Abstract Microreactors attract a significant interest for chemical synthesis due to the benefits of small scales such as high surface to volume ratio, rapid thermal ramping, and well-understood laminar flows. The suitability of atomic layer deposition for application of both the nanoparticle catalyst and the support material on the surfaces of channels of microfabricated silicon microreactors is demonstrated in this research. Continuous-flow hydrogenation of propene into propane at low temperatures with TiO₂-supported catalytic Pt nanoparticles was used as a model reaction. Reaction yield and mass transport were monitored by high-sensitivity microcoil NMR spectroscopy as well as time-of-flight remote detection NMR imaging. The microreactors were shown to be very efficient in propene conversion into propane. The yield of 100 % was achieved at 50 °C with a reactor decorated with Pt nanoparticles of average size of roughly 1 nm and surface coverage of 3.2 % in 20 mm long reaction channels with a residence time of 1100 ms. The activity of the Pt catalyst surfaces was on the order of several to tens of mmol s−1 m−2

Fracture properties of atomic layer deposited aluminum oxide free-standing membranes

Peer reviewe