Timo Hatanpää

Atomic layer deposition of metal tellurides and selenides using alkylsilyl compounds of tellurium and selenium.

Atomic layer deposition (ALD) of metal selenide and telluride thin films has been limited because of a lack of precursors that would at the same time be safe and exhibit high reactivity as required in ALD. Yet there are many important metal selenide and telluride thin film materials whose deposition by ALD might be beneficial, for example, CuInSe2 for solar cells and Ge2Sb2Te5 for phase-change random-access memories. Especially in the latter case highly conformal deposition offered by ALD is essential for high storage density. By now, ALD of germanium antimony telluride (GST) has been attempted only using plasma-assisted processes owing to the lack of appropriate tellurium precursors. In this paper we make a breakthrough in the development of new ALD precursors for tellurium and selenium. Compounds with a general formula (R3Si)2Te and (R3Si)2Se react with various metal halides forming the corresponding metal tellurides and selenides. As an example, we show that Sb2Te3, GeTe, and GST films can be deposited by ALD using (Et3Si)2Te, SbCl3, and GeCl2 x C4H8O2 compounds as precursors. All three precursors exhibit a typical saturative ALD growth behavior and GST films prepared at 90 degrees C show excellent conformality on a high aspect-ratio trench structure.

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.

Study of a novel ALD process for depositing MgF2 thin films

Magnesium fluoride is an ultraviolet (UV) transparent material which is widely used in optical applications over a wide wavelength range. We have developed a novel atomic layer deposition (ALD) process for depositing magnesium fluoride thin films for the first time. MgF2 films were grown at 250–400 °C using Mg(thd)2 and TiF4 as precursors. The crystallinity, morphology, composition, thicknesses and refractive indices of the films were analyzed by X-ray diffraction/reflection (XRD/XRR), transmission electron microscopy (TEM), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), time-of-flight elastic recoil detection analysis (TOF-ERDA), and UV-vis spectrophotometry. Electrical properties were also measured. The growth rate was temperature dependent decreasing from 1.6 A cycle−1 at 250 °C to 0.7 A cycle−1 at 400 °C. The films were polycrystalline at 250–400 °C. The refractive indices were between 1.34–1.42 and the permittivity 4.9. The impurity levels were below 0.6 at.% in the films deposited at 350–400 °C.

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).

Electrical Properties of Atomic-Layer-Deposited Thin Gadolinium Oxide High-k Gate Dielectrics

Amorphous or cubic Gd2O3 thin films were grown from tris ( 2,3-dimethyl-2-butoxy)gadolinium( III) , Gd [OC(CH3)(2)CH(CH3)(2))(3)], and H2O precursors at 350 degrees C. As-deposited Gd2O3 films grown on etched (H-terminated) Si(100) exhibited better leakage current-voltage characteristics as well as lower flatband voltage shift than films grown on SiO2/ Si substrates. Interface trap densities were lower in Al/Gd2O3/ hydrofluoric acid (HF)-etched Si samples annealed at rather high temperatures.

Iridium metal and iridium oxide thin films grown by atomic layer deposition at low temperatures

Atomic layer deposition (ALD) of both iridium and iridium oxide films at low temperatures has been studied and the resulting films have been examined by XRD, FESEM, XRR, EDX, AFM, TOF-ERDA, and four point probe measurements. Iridium oxide films were successfully grown using (MeCp)Ir(CHD) and ozone between 100 and 180 °C, however, the density of the films substantially reduced at 120 °C and below. The density reduction was accompanied by a phase change from crystalline to amorphous IrO2. Metallic iridium films were deposited between 120 and 180 °C by adding a reductive hydrogen pulse after the oxidative ozone pulse. Comparison of these processes with the earlier process employing the same Ir precursor with molecular oxygen is also made. The (MeCp)Ir(CHD)–O3–H2 process is able to produce metallic films at about 100 °C lower temperature than the oxygen based process.

MeCp)Ir(CHD) and molecular oxygen as precursors in atomic layer deposition of iridium

Iridium thin films were grown by atomic layer deposition (ALD) between 225 and 350 °C using (MeCp)Ir(CHD) (MeCp = methylcyclopentadienyl, CHD = cyclohexadiene) and molecular oxygen as precursors. (MeCp)Ir(CHD) precursor was synthesized and characterized in-house. Also the crystal structure of (MeCp)Ir(CHD) is reported. All the ALD grown Ir films passed a common tape test indicating a good adhesion on Al2O3 nucleation layer. Quite untypically, surface roughness was the highest on films deposited at 225–250 °C and decreased strongly by increasing deposition temperature. Partial decomposition of the (MeCp)Ir(CHD) precursor resulted in defects on the film surface at 350 °C. Ir thin films with good quality were obtained at the deposition temperatures of 275 and 300 °C. A 50 nm thick film grown at 275 °C had a roughness of 1.2 nm, contained about 3 at% oxygen, 0.6 at% carbon and 1.6 at% hydrogen impurities, while the resistivity was as low as 9 µΩ cm.

Study of amorphous lithium silicate thin films grown by atomic layer deposition

Lithium silicate thin films, which are interesting materials for example in lithium ion batteries, were grown by the atomic layer deposition technique from lithium hexamethyldisilazide [LiHMDS, Li(N(SiMe3)2)] and ozone precursors. Films were obtained at a wide deposition temperature range between 150 and 400 °C. All the films were amorphous except at 400 °C, where partial decomposition of LiHMDS was also observed. The growth behavior was examined in detail at 250 °C, and saturation of growth rates and refractive indices with precursor doses was confirmed, thereby verifying self-limiting surface reactions. Likewise, the linear thickness dependence of the films with the number of deposition cycles was verified. Strong dependence of growth rate and film composition on deposition temperature was also seen. Overall, the amorphous films grown at 250 °C had a stoichiometry close to lithium metasilicate (Li2.0SiO2.9) with 0.7 at. % carbon and 4.6 at. % hydrogen impurities. The corresponding growth rate and refrac...

Volatile β-diketonato Complexes of Ruthenium, Palladium and Platinum. Preparation and Thermal Characterization

Ruthenium, palladium and platinum complexes of 2,2,6,6-tetramethyl-3,5-heptanedione (thd) and ruthenium tris acetylacetonate (acac) were synthetized and studied with TG, DTA, DSC and MS methods. Thermal properties of ruthenocene were also studied. The platinum thd complex has the highest volatility despite the second highest molecular mass of the complex. All the complexes sublimed under reduced pressure. Ru(acac)3 decomposed during sublimation under atmospheric pressure of nitrogen whereas the other compounds studied sublimed also under these conditions. Pd(thd)2 reduced under atmospheric pressure of H2 /N2 (5% H2 ) whereas the ruthenium complexes were not reduced. The field desorption mass spectra of complexes showed only the molecular peaks and no fragmentation occurred.

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.