Marko Vehkamäki

Atomic Layer Deposition of SrTiO3 Thin Films from a Novel Strontium Precursor–Strontium-bis(tri-isopropyl cyclopentadienyl)

Strontium titanate thin films were grown by atomic layer deposition (ALD) at 250–325 °C from the novel strontium compound, strontium bis(tri-isopropyl cyclopentadienyl), titanium tetraisopropoxide, and water. Though completely self-limiting, deposition of strontium could not be achieved because of some minor decomposition of the strontium compound. This decomposition was slow enough to ensure that good control of film stoichiometry was obtained by controlling either the (Sr-O)/(Ti-O) pulsing ratio, or the strontium precursor exposure time. The films were polycrystalline and strongly oriented in the (100) direction. After annealing at 500 °C in air, the films with the optimal composition were found to have measured permittivity values of around 180.

Bismuth precursors for atomic layer deposition of bismuth-containing oxide films

Several bismuth amides and a bismuth thioamidate compound were synthesized and characterized in order to find volatile bismuth precursors for atomic layer deposition (ALD) of oxide materials. Crystal structures of Bi(N(SiMe3)2)3 and Bi(SC(Me)NPri)3 are reported. Based on precursor characterization Bi(N(SiMe3)2)3 was selected for film deposition experiments. It was found that alternate surface reactions of Bi(N(SiMe3)2)3 and H2O can be used for ALD of amorphous BiOx, Bi–Ta–O and Sr–Bi–Ta–O at 190–200 °C. After post-deposition annealing at 800 °C in oxygen the SrBi2Ta2O9 layered perovskite phase was obtained.

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3.

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).

Deposition of molybdenum thin films by an alternate supply of MoCl5 and Zn

Molybdenum thin films were deposited onto both soda lime glass and Al2O3 film by an alternate supply of MoCl5 and Zn. Zinc was used as a reducing agent. The film growth was performed over a temperature range of 400–500u2009°C in order to study the temperature effect on the growth. In addition to the growth temperature, the purge length after zinc was also seen to have a considerable effect on the growth. The films were analyzed by energy dispersive x-ray spectroscopy, scanning electron microscopy, elastic recoil detection analysis, x-ray diffraction and four point resistance measurements in order to determine their chemical and physical characteristics.

Conformality of remote plasma-enhanced atomic layer deposition processes: An experimental study

In total, five metal oxide and one metal plasma-enhanced atomic layer deposition (PEALD) processes were studied with respect to the conformality of the coatings. The study reveals that also high aspect ratio structures (up to 60:1) can be coated conformally with remote PEALD. Oxides could relatively easily be deposited into demanding 3D structures with rather short cycle times but not the silver metal. The key factor in achieving excellent conformality seems to be that sufficient radical density is required to overcome the loss of radicals by recombination. In the case of metals where hydrogen plasma is applied the recombination of hydrogen radicals causes major difficulties in obtaining perfect conformality.

Diffusion Barrier Properties of Atomic Layer Deposited Ultrathin Ta2O5 and TiO2 Films

Diffusion barrier properties of ultrathin Ta 2 O 5 and TiO 2 films deposited by the atomic layer deposition (ALD) method were investigated. The oxide films were deposited using well-defined deposition processes with metal alkoxides and water as precursors. Tantalum oxide films were deposited from tantalum pentaethoxide and water and titanium dioxide films from titanium tetramethoxide and water, both at 240°C. The films examined in the diffusion barrier tests were in the thickness range of 1 - 4 nm. The breakdown temperatures of the annealed Cu/barrier/Si structures were determined from the increase in the sheet resistance, X-ray diffraction data, and etch-pit test results. From the studied barrier films, the 3-nm-thick titanium dioxide film was found to possess the best resistance to copper diffusion as the first etch pits were observed only after the annealing at 650°C.

Atomic Layer Deposition of Strontium Tantalate Thin Films from Bimetallic Precursors and Water

Strontium tantalate thin films were grown with atomic layer deposition at 200-350°C using bimetallic donor-functionalized alkoxides and water as precursors. SrTa 2 (OEt) 10 (dmae) 2 (dmae = dimethylaminoethoxide) was found to be a suitable atomic layer deposition precursor for depositing SrTa 2 O 6 films with compositions very close to the 1:2 metal ratio found in the precursor. Film compositions and impurity levels were studied with Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. The as-deposited films were amorphous, but after annealing in air at 800°C orthorhombic SrTa 2 O 6 was observed. Dielectric permittivities were 16 and 50 for as-deposited films and for films annealed in air at 800°C, respectively.

Sealing of hard CrN and DLC coatings with atomic layer deposition

Atomic layer deposition (ALD) is a thin film deposition technique that is based on alternating and saturating surface reactions of two or more gaseous precursors. The excellent conformality of ALD thin films can be exploited for sealing defects in coatings made by other techniques. Here the corrosion protection properties of hard CrN and diamond-like carbon (DLC) coatings on low alloy steel were improved by ALD sealing with 50 nm thick layers consisting of Al2O3 and Ta2O5 nanolaminates or mixtures. In cross sectional images the ALD layers were found to follow the surface morphology of the CrN coatings uniformly. Furthermore, ALD growth into the pinholes of the CrN coating was verified. In electrochemical measurements the ALD sealing was found to decrease the current density of the CrN coated steel by over 2 orders of magnitude. The neutral salt spray (NSS) durability was also improved: on the best samples the appearance of corrosion spots was delayed from 2 to 168 h. On DLC coatings the adhesion of the ALD sealing layers was weaker, but still clear improvement in NSS durability was achieved indicating sealing of the pinholes.

Atomic layer deposition and characterization of Bi₂Te₃ thin films.

Bi2Te3 thin films were deposited by atomic layer deposition (ALD) from BiCl3 and (Et3Si)2Te at 160-300 °C. The process was studied in detail, and growth properties typical of ALD were verified. Films were stoichiometric with low impurity content. The film thickness was easily controlled with the number of deposition cycles. Properties of the ALD Bi2Te3 thin films were found to be comparable to those reported in literature for Bi2Te3 films made by other methods. Films crystallized to a rhombohedral phase, and there was a preferred orientation to the growth. Electrical and thermoelectric properties were also determined to be comparable to literature values.

Passivation of copper surfaces for selective-area ALD using a thiol self-assembled monolayer

Self-assembled monolayers (SAMs) of 1-dodecanethiol (CH3(CH2)11SH) were prepared from the vapor phase and used as a passivation layer for selective-area ALD. Thiol SAMs have commonly been prepared by immersing the substrates into a solution containing alkyl thiols. Formation of SAMs from the vapor phase, however, has advantages compared to liquid phase preparation. Passivation of surface can be done as a part of the ALD process forming a SAM first and then continuing with the common ALD process. SAMs can also be applied to three-dimensional structures relying on chemical selectivity of the thiol SAM formation. For example in the copper damascene process the thiol SAMs should form only on the copper surface but not on the insulators. In this study, the SAMs were prepared by placing the substrate and the alkylthiol to the reaction chamber and heating the system to the temperature of 73 ?C. Preparation time varied from 0.5 to 24 h. Passivation properties of SAMs were tested with ALD iridium and polyimide processes. Iridium was deposited at 250? ? C for 500 cycles and polyimide at 160? ? C for 20 cycles.