Timo Sajavaara

Effect of water dose on the atomic layer deposition rate of oxide thin films

Abstract The growth rate and properties of atomic layer deposited (ALD) Al 2 O 3 thin films were examined by varying the water dose in the Al(CH 3 ) 3 -H 2 O process at growth temperatures of 150–500°C. When the growth rate was followed as a function of water pulse time, it was found to saturate with both small and large water doses but the saturated level was substantially higher for the large water dose, 1.2 vs. 1.0 A/cycle. This increase was attributed to an increased hydroxyl group density on the film surface after the water pulse. The effect of the water dose was examined also in other ALD oxide processes where in most cases the growth rate increased by 24 to 86%, in the best cases even doubled, though in a few other cases the effect was minimal. No major differences were found in the properties of the films grown with small and large water doses.

Atomic Layer Deposition of Hafnium Dioxide Films from Hafnium Tetrakis(ethylmethylamide) and Water

HfO 2 films were produced from Hf[N(CH 3 )(C 2 H 5 )] 4 and H 2 O, on borosilicate glass, indium-tin-oxide (ITO), and Si(100) substrates, in the temperature range 150-325 °C, using atomic layer deposition (ALD). In the temperature range 200-250 °C, the growth rate of the HfO 2 films was 0.09 nm per cycle, but increased with both increasing and decreasing temperatures. The self-limiting adsorption of Hf[N(CH 3 )(C 2 H 5 )] 4 at 250 °C was verified. The films were stoichiometric dioxides with an O/Hf ratio of 2.0 ± 0.1. The concentrations of residual carbon, nitrogen, and hydrogen, determined using ion beam analysis, were 0.3-0.6 at.-%, 0.1-0.2 at.-%, and 2-3 at.-%, respectively. The films crystallized at growth temperatures exceeding 150-175 °C, and consisted mainly of the monoclinic HfO 2 phase. The refractive index of the films varied between 2.08 and 2.10. The effective permittivities of the HfO 2 films grown in the temperature range 200-300°C varied between 11 and 14.

Short-ranged structural rearrangement and enhancement of mechanical properties of organosilicate glasses induced by ultraviolet radiation

The short-ranged bonding structure of organosilicate glasses can vary to a great extent and is directly linked to the mechanical properties of the thin film material. The combined action of ultraviolet (UV) radiation and thermal activation is shown to generate a pronounced rearrangement in the bonding structure of thin organosilicate glass films involving no significant compositional change or film densification. Nuclear magnetic resonance spectroscopy indicates loss of –OH groups and an increase of the degree of cross-linking of the organosilicate matrix for UV-treated films. Fourier transform infrared spectroscopy shows a pronounced enhancement of the Si–O–Si network bond structure, indicating the formation of more energetically stable silica bonds. Investigation with x-ray reflectivity and ellipsometric porosimetry indicated only minor film densification. As a consequence, the mechanical properties of microporous organosilicate dielectric films are substantially enhanced while preserving the organosili...

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.

Detection efficiency of time-of-flight energy elastic recoil detection analysis systems

Abstract The detection efficiency of recoils with masses ranging from H up to Nb at energies from 0.05 to 1 MeV per nucleon has been investigated for Time-of-Flight Energy Elastic Recoil Detection (ToF-E ERD) systems. It is observed that the detection efficiency for the ToF-E detector telescope depends on the stopping power in the carbon foils, which in turn relies upon the recoil mass and energy. Furthermore, the limits of this behaviour depend on the setting of the discriminator thresholds. The detection efficiency of a time detector could be fitted to a universal curve that can be described by a simple empirical formula as a function of recoil electronic stopping power in the carbon foil. This formula can be used to predict the detection efficiency by recoil energy for N, O and other elements, for which it may not be easy to prepare suitable reference samples containing only that element.

Properties of hafnium oxide films grown by atomic layer deposition from hafnium tetraiodide and oxygen

Polycrystalline monoclinic HfO2 films were atomic layer deposited on Si(100) substrates by a nonhydrous carbon-free process of HfI4 and O2. The oxygen to hafnium ratio corresponded to the stoichiometric dioxide within the limits of accuracy of ion beam analysis. A 1.5–2.0 nm thick SiO2 interface layer formed between the HfO2 films and Si substrates. Hysteresis of the capacitance–voltage curves was observed in Al/HfO2/p-Si(100) structures with oxide grown in the substrate temperature range of 570–755 °C. The hysteresis ceased with an increase in O2 pressure. The effective permittivity of the dielectric layers varied between 12 and 16. The breakdown voltages were found to be lower in the case of higher oxygen doses and higher HfO2 deposition temperatures.

Atomic layer deposition of polyimide thin films

The atomic layer deposition (ALD) of different polyimide thin films has been studied. We have demonstrated self-limiting ALD deposition of PMDA–DAH, PMDA–EDA, PMDA–ODA and PMDA–PDA thin films at 160 °C. The maximum deposition rate of 5.8 A cycle−1 was obtained for the PMDA–DAH process. Although the deposition rate was high at 160 °C, a sudden decrease was observed when the temperature was increased. Regardless of the process studied, no film growth was obtained at 200 °C or above. Deposited polyimide films were analysed by FTIR, AFM and TOF-ERDA. According to the FTIR measurements, imide bonds were formed already in as-deposited films indicating polyimide formation without any additional thermal treatment.

Low-Temperature ALE Deposition of Y2O3 Thin Films from β-Diketonate Precursors

Yttrium oxide thin film deposition by atomic layer epitaxy (ALE) was studied at 200-425 °C using Y(thd) 3 , Y(thd) 3 (bipyridyl), or Y(thd) 3 (1,10-phenanthroline) (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) as an yttrium precursor, and ozone as an oxygen source. All yttrium precursors were analyzed by thermogravimetry/differential thermal analysis (TG-DTA) and mass spectrometry (MS). Soda lime glass and Si(100) were used as substrates. With all precursors, a constant deposition rate of 0.22-0.23 A (cycle) -1 was observed at 250-350 °C on both substrates, indicating a surface-controlled growth and similar surface species at the deposition temperatures used. The effect of growth parameters, such as reactant pulsing times, was investigated in detail at 350 °C using Y(thd) 3 . Deposited films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to determine crystallinity and surface morphology, while ion-beam analysis and X-ray photoelectron spectroscopy (XPS) were used to analyze stoichiometry and impurity levels. Infrared (IR) measurements were performed to determine the type of carbon impurity. Crystalline films with a (400) dominant orientation were obtained when depositions were carried out within the ALE window (temperature range of 250-375 °C), but films deposited below 250 °C were nearly amorphous. Preferential orientation changed from (400) to (222) when deposition temperatures were raised slightly above the ALE window to 375 °C, where a partial decomposition of Y(thd) 3 probably takes place. Judging from the impurity levels of the films and growth rates, the adducting of Y(thd) 3 does not bring about any advantages in the ALE growth of Y 2 O 3 .

Atomic Layer Deposition of Ta(Al)N(C) Thin Films Using Trimethylaluminum as a Reducing Agent

Ta(Al)N(C) thin films were deposited by the atomic layer deposition technique using TaCl 5 or TaBr 5 and NH 3 as precursors and Al(CH 3 ) 3 as an additional reducing agent. For comparison TaN thin films were deposited also from TaBr 5 and NH 3 with and without Zn. The films were analyzed by means of the time-of-flight elastic recoil detection analysis, energy dispersive X-ray spectroscopy, X-ray diffraction, and standard four-point probe method. The deposition temperature was varied between 250 and 400°C. The films contained aluminum, carbon, hydrogen, and chlorine impurities. The chlorine content decreased drastically as the deposition temperature was increased. The film deposited at 400°C contained less than 4 atom % chlorine and also had the lowest resistivity. 1300 μΩ cm. The barrier properties of the Cu/Ta(Al)N(C)/Si structure were studied by using sheet resistance and X-ray diffraction measurements.

Surface-controlled growth of LaAlO3 thin films by atomic layer epitaxy

LaAlO3 thin films were deposited by atomic layer epitaxy (ALE) from β-diketonate-type precursors La(thd)3 and Al(acac)3. Ozone was used as an oxygen source. Films were grown on soda lime glass, Si(100), MgO-buffered Si(100), sapphire and SrTiO3(100) substrates. The influence of the La∶Al precursor pulsing ratio on the film growth and quality in the temperature range of 325–400 °C was studied in detail. Stoichiometry and impurity levels were measured using RBS, TOF-ERDA and XPS while the chemical type of carbon impurity was identified by FTIR. XRD and AFM were used to determine crystallinity and surface morphology. The films were transparent and uniform and their thickness could be accurately controlled by the number of deposition cycles. The as-deposited films were amorphous but became crystalline upon annealing at 900 °C. The annealed films grown on Si(100) and MgO(111)-buffered Si(100) substrates had a preferred (110) orientation whereas those grown on MgO(100)-buffered Si(100) substrates showed a preferred (100) orientation. Epitaxial and smooth LaAlO3 thin films were obtained on SrTiO3(100) after annealing at 900 °C, verified by measurement of the X-ray rocking curve of the (200) reflection and the AFM surface roughness. Stoichiometric LaAlO3 films contained <1.9 atom% carbon and about 0.3 atom% hydrogen as impurities.