Atomic Layer Deposition of Multicomponent Oxide Materials

Atomic layer deposition (ALD) is a method for thin film deposition which has been extensively studied for binary oxide thin film growth. Studies on multicomponent oxide growth by ALD remain relatively few owing to the increased number of factors that come into play when more than one metal is employed. More metal precursors are required, and the surface may change significantly during successive stages of the growth. Multicomponent oxide thin films can be prepared in a well-controlled way as long as the same principle that makes binary oxide ALD work so well is followed for each constituent element: in short, the film growth has to be self-limiting. ALD of various multicomponent oxides was studied. SrTiO3, BaTiO3, Ba(1-x)SrxTiO3 (BST), SrTa2O6, Bi4Ti3O12, BiTaO4 and SrBi2Ta2O9 (SBT) thin films were prepared, many of them for the first time by ALD. Chemistries of the binary oxides are shown to influence the processing of their multicomponent counterparts. The compatibility of precursor volatilities, thermal stabilities and reactivities is essential for multicomponent oxide ALD, but it should be noted that the main reactive species, the growing film itself, must also be compatible with self-limiting growth chemistry. In the cases of BaO and Bi2O3 the growth of the binary oxide was very difficult, but the presence of Ti or Ta in the growing film made self-limiting growth possible. The application of the deposited films as dielectric and ferroelectric materials was studied. Post-deposition annealing treatments in different atmospheres were used to achieve the desired crystalline phase or, more generally, to improve electrical properties. Electrode materials strongly influenced the leakage current densities in the prepared metal insulator metal (MIM) capacitors. Film permittivities above 100 and leakage current densities below 110-7 A/cm2 were achieved with several of the materials.Monikomponenttioksidit eli useampaa metallista alkuainetta sisältävät oksidit ovat yleisiä luonnossa ja muodostavatkin suuren osan maapallon kuorikerroksesta. Synteettiset monikomponenttioksidit, kuten esimerkiksi BaTiO3, ovat tärkeitä materiaaleja teknisissä sovelluksissa, kuten erilaisissa elekroniikan komponenteissa ja mm. ultraäänikuvauslaitteissa ja kaikuluotaimissa. Ohutkalvot ovat alle mikrometrin tai jopa vain muutaman nanometrin paksuisia kerroksia. Mikropiirejä, esimerkiksi muistipiirejä ja mikroprosessoreita, valmistettaessa tarvitaan eri tavoilla sähköä johtavia ohutkalvokerroksia. Atomikerroskasvatus (Atomic Layer Deposition, ALD) on Suomessa 1970-luvulla kehitetty ohutkalvojen valmistusmenetelmä. ALD-menetelmässä kalvot kasvatetaan itserajoittavilla pintareaktioilla, joissa syntyy osa atomikerroksesta. Reaktioiden itserajoittavuudesta on useita etuja. Syntyvän kalvon paksuutta on helppo säädellä reaktioiden määrällä ja kalvot kasvavat tasaisesti suurillekin pinnoille ja myös pinnoitettavissa kappaleissa oleviin uriin tai huokosiin. ALD-menetelmällä voidaan pinnoittaa myös jauheita, millä voi olla käyttöä esimerkiksi katalyyttien valmistuksessa. Tässä väitöskirjatyössä tutkittiin SrTiO3, BaTiO3, Ba(1-x)SrxTiO3, SrTa2O6, Bi4Ti3O12, BiTaO4 ja SrBi2Ta2O9 ohutkalvojen valmistusta ALD-menetelmällä. Tutkitut materiaalit ovat mahdollisia tulevaisuuden muistipiirien eristäviä tai ferroelektrisiä materiaaleja. Kalvojen matalista kasvatuslämpötiloista (190 340 °C) johtuen materiaaleille on tehtävä lämpökäsittelyjä korkeissa lämpötiloissa (500 850 °C), jotta ne saataisiin kiteytymään. Kalvomateriaalien sähköisiä ominaisuuksia tutkittiin käyttämällä niitä testikondensaattorien eristeinä. Tutkituille kalvomateriaalille mitattiin korkeita, yli 100:n, suhteellisia permittiivisyyksiä. Parhaimmillaan kondensaattorien vuotovirrat olivat alle 110-7 A/cm2 yhden voltin jännitteellä. Työssä saadut tulokset osoittavat, että ALD on toimiva menetelmä ohuiden monikomponenttioksidikalvojen valmistukseen

Highly Material Selective and Self-Aligned Photo-assisted Atomic Layer Deposition of Copper on Oxide Materials

There is a growing need for bottom-up fabrication methods in microelectronic industry as top-down, lithography-based methods face increasing challenges. In Photo-assisted atomic layer deposition (Photo-ALD), photons supply energy to the deposition reactions on the surface. Here, a process and patterning for Photo-ALD of copper is reported, with inherently selective, self-aligned film growth without any photomasking or additive layers. Highly conductive and pure copper films are selectively deposited on tantalum oxide for over hundred nanometers of film thickness, while no copper deposits on silicon or aluminum oxide. On anatase titanium dioxide, copper deposition is crystal-facet selective. Selective deposition of a metal is realized on oxides, which has been especially challenging for ALD. This study indicates that the growth mechanism is closely related to photocatalysis: the photons interact with the material under the growing copper film, enabling the inherent selectivity. The findings provide promising material engineering schemes for microelectronics, photocatalysis, and photovoltaics.Peer reviewe

Area-Selective Molecular Layer Deposition of Polyimide on Cu through Cu-Catalyzed Formation of a Crystalline Interchain Polyimide

Novel area-selective molecular layer deposition (AS-MLD) of polyimide (PI) on Cu versus native SiO2 was studied. By use of 1,6-diaminohexane (DAH) and pyromellitic dianhydride (PMDA) as precursors, PI films can be selectively deposited on the Cu surface at 200-210 degrees C with a rate around 7.8 A/cycle while negligible growth takes place on SiO2. The selectivity was successfully demonstrated also on Cu/SiO2 patterns at 200 degrees C; after 180 MLD cycles, around 140 nm thick PI was deposited on Cu regions whilePeer reviewe

Atomic layer deposition of GdF3 thin films

doi: 10.1116/6.0001629Gadolinium fluoride is an attractive optical material with applications in, e.g., deep-UV lithography, solar cells, and medical imaging. Despite the interest toward this material, no atomic layer deposition (ALD) process has been published. In this article, an ALD process for GdF3 using Gd(thd)(3) and NH4F as precursors is presented. The deposition was studied at temperatures 275-375 & DEG;C, but 285-375 & DEG;C produce the purest films. The saturation of the growth per cycle (GPC) with respect to precursor pulses and purges was proved at 300 & DEG;C. The GPC value at this temperature is & SIM;0.26 & ANGS;, and the deposition temperature has very little effect on the GPC. According to x-ray diffraction, all the films consist of orthorhombic GdF3. The impurity contents, evaluated by time-of-flight elastic recoil detection analysis, is low, and the films are close to stoichiometric. The nitrogen content is less than < 0.04 at. %. The antireflection properties were qualitatively evaluated by UV-vis spectrometry in a transmission mode at a 190-1100 nm range: on sapphire substrates, GdF3 serves as an antireflective coating. Dielectric properties of the films were studied, and for example, a permittivity value of 9.3 was measured for a & SIM;64 nm film deposited at 300 & DEG;C.Peer reviewe

Atomic Layer Deposition of Insulating AlF3/Polyimide Nanolaminate Films

This article describes the deposition of AlF3/polyimide nanolaminate film by inorganic-organic atomic layer deposition (ALD) at 170 °C. AlCl3 and TiF4 were used as precursors for AlF3. Polyimide layers were deposited from PMDA (pyromellitic dianhydride, 1,2,3,5-benzenetetracarboxylic anhydride) and DAH (1,6-diaminohexane). With field-emission scanning electron microscopy (FESEM) and X-ray reflection (XRR) analysis, it was found that the topmost layer (nominally 10 nm in thickness) of the nanolaminate film (100 nm total thickness) changed when exposed to the atmosphere. After all, the effect on roughness was minimal. The length of a delay time between the AlF3 and polyimide depositions was found to affect the sharpness of the nanolaminate structure. Electrical properties of AlF3/polyimide nanolaminate films were measured, indicating an increase in dielectric constant compared to single AlF3 and a decrease in leakage current compared to polyimide films, respectively

(Invited) Photo-Assisted ALD : Process Development and Application Perspectives

Atomic layer deposition (ALD) is a highly versatile thin-film deposition method that is presently utilized in many steps within microelectronic process flow and is gaining more and more interest in other fields of industry as well. The prosperity of ALD originates from its capability to controllably deposit high-quality films uniformly and conformally over large areas and complicated features. However, one of the main challenges of ALD, lateral control of film growth, stems from these same properties. Selective-area ALD (S-ALD) is presently a subject of intense research and development work as the targeted feature sizes in the semiconductor applications have reduced to a level exceeding the capabilities of lithography methods. Photo-assisted ALD (Photo-ALD) is a less-studied approach to facilitate S-ALD and selection of materials accessible with Photo-ALD is scarce. The present paper contributes to this field by reporting studies on Photo-ALD processes for metal oxides and metals.Atomic layer deposition (ALD) is a highly versatile thin-film deposition method that is presently utilized in many steps within microelectronic process flow and is gaining more and more interest in other fields of industry as well. The prosperity of ALD originates from its capability to controllably deposit high-quality films uniformly and conformally over large areas and complicated features. However, one of the main challenges of ALD, lateral control of film growth, stems from these same properties. Selective-area ALD (S-ALD) is presently a subject of intense research and development work as the targeted feature sizes in the semiconductor applications have reduced to a level exceeding the capabilities of lithography methods. Photo-assisted ALD (Photo-ALD) is a less-studied approach to facilitate S-ALD and selection of materials accessible with Photo-ALD is scarce. The present paper contributes to this field by reporting studies on Photo-ALD processes for metal oxides and metals.Peer reviewe

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition

Abstract Rhenium is both a refractory metal and a noble metal that has attractive properties for various applications. Still, synthesis and applications of rhenium thin films have been limited. We introduce herein the growth of both rhenium metal and rhenium nitride thin films by the technologically important atomic layer deposition (ALD) method over a wide deposition temperature range using fast, simple, and robust surface reactions between rhenium pentachloride and ammonia. Films are grown and characterized for compositions, surface morphologies and roughnesses, crystallinities, and resistivities. Conductive rhenium subnitride films of tunable composition are obtained at deposition temperatures between 275 and 375 °C, whereas pure rhenium metal films grow at 400 °C and above. Even a just 3 nm thick rhenium film is continuous and has a low resistivity of about 90 µΩ cm showing potential for applications for which also other noble metals and refractory metals have been considered.Peer reviewe

Resistless fabrication of embedded nanochannels by FIB patterning, wet etching and atomic layer deposition

Self-supported SiO2 structures were fabricated from thermal SiO2/Si substrates by combining FIB direct writing and selective and anisotropic chemical wet etching of silicon. These structures, such as SiO2 overhangs on the edges of Si trenches, were then used as templates for ALD of Ta2O5 to form sealed nanochannels and cavities. The size of trenches formed by etching through openings in the SiO2 increases with FIB patterning ion dose as well as KOH etching time. Channel formation results from sealing the trenches by the conformal ALD of Ta2O5. The KOH etching time determines the channel size while the ion dose determines final wall thickness after ALD. The fabricated hollow nanochannels are embedded under SiO2 and surrounded by Ta2O5 on crystalline Si. The channel size reaches 50 nm by this fabrication approach with a 60 min KOH etching time.Peer reviewe

Hydrogen release from liquid organic hydrogen carriers catalysed by platinum on rutile-anatase structured titania

A liquid organic hydrogen carrier (LOHC) is an interesting concept for hydrogen storage. We describe herein a new, active catalyst system for dehydrogenation of perhydrogenated dibenzyl toluene (H18-DBT), which is a promising LOHC candidate. Pt supported on a rutile-anatase form of titania was found to be more active than Pt supported on anatase-only titania, or on alumina, and almost equally active as Pt supported on carbon. Robust and durable metal oxide supports are preferred for catalysing reactions at high temperatures.Peer reviewe

Novel electroblowing synthesis of tin dioxide and composite tin dioxide/silicon dioxide submicron fibers for cobalt(II) uptake

Nanoscale SnO2 has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO2 and composite SnO2/SiO2 submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures and morphologies. In all the fibers SnO2 was detected by XRD indicating the SnO2/SiO2 fibers to be composite instead of complete mixtures. We studied the Co2+ separation ability of the fibers, since Co-60 is a problematic contaminant in nuclear power plant wastewaters. Both SnO2 and SnO2/SiO2 fibers had an excellent Co2+ uptake with their highest uptake/K-d values being 99.82%/281 000 mL g(-1) and 99.79%/234 000 mL g(-1), respectively. Compared to the bare SnO2 fibers, the SiO2 component improved the elasticity and mechanical strength of the composite fibers which is advantageous in dynamic column operation.Peer reviewe