Film conformality and extracted recombination probabilities of O atoms during plasma-assisted atomic layer deposition of SiO2, TiO2, Al2O3, and HfO2

Surface recombination of plasma radicals is generally considered to limit film conformality during plasma-assisted atomic layer deposition (ALD). Here, we experimentally studied film penetration into high-aspect-ratio structures and demonstrated that it can give direct information on the recombination probability r of plasma radicals on the growth surface. This is shown for recombination of oxygen (O) atoms on SiO2, TiO2, Al2O3, and HfO2 where a strong material dependence has been observed. Using extended plasma exposures, films of SiO2 and TiO2 penetrated extremely deep up to an aspect ratio (AR) of ∼900, and similar surface recombination probabilities of r = (6 ± 2) × 10–5 and (7 ± 4) × 10–5 were determined for these processes. Growth of Al2O3 and HfO2 was conformal up to depths corresponding to ARs of ∼80 and ∼40, with r estimated at (1–10) × 10–3 and (0.1–10) × 10–2, respectively. Such quantitative insight into surface recombination, as provided by our method, is essential for modeling radical-surface interaction and understanding for which materials and conditions conformal film growth is feasible by plasma-assisted ALD

Sticking probabilities of H2O and Al(CH3)3 during atomic layer deposition of Al2O3 extracted from their impact on film conformality

The conformality of a film grown by atomic layer deposition (ALD) is strongly affected by the reactivities of the precursor and coreactant, which can be expressed in terms of their sticking probabilities toward the surface. We show that the leading front of the thickness profile in high-aspect-ratio structures gives direct information on the sticking probabilities of the reactants under most conditions. The slope of the front has been used to determine the sticking probabilities of Al(CH3)3 and H2O during ALD of Al2O3. The determined values are (0.5–2) × 10−3 for Al(CH3)3 and (0.8–2) × 10−4 for H2O at a set-point temperature of 275 °C, corresponding to an estimated substrate temperature of ∼220 °C. Additionally, the thickness profiles reveal soft-saturation behavior during the H2O step, most dominantly at reduced temperatures, which can limit the conformality of Al2O3 grown by ALD. This work thus provides insights regarding quantitative information on sticking probabilities and conformality during ALD, which is valuable for gaining a deeper understanding of ALD kinetics

Growth of aluminum nitride on porous alumina and silica through separate saturated gas-solid reactions of trimethylaluminum and ammonia

Aluminum nitride-type species were prepared on porous alumina and silica by repeated separate, saturated reactions of gaseous trimethylaluminum (TMA) and ammonia with solid substrates. Reaction cycles of TMA at 423 K and ammonia at 823 K were performed up to six times. Growth per cycle was on average 2.4 AlN units/nm2, but it increased slightly with the number of reaction cycles. The amount of hydrogen present in NHx groups increased with the increasing number of reaction cycles. AlN4 units were observed by 27Al NMR on alumina, but the AlN remained amorphous to X-ray diffraction. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy revealed that the AlN-type species were spread out evenly on the surface of the particles. TMA reacted with equal probability with the still-exposed silica and the AlN-type species present on the surface, as shown by low-energy ion scattering. 29Si and 27Al NMR suggested that transition from the oxide substrates to aluminum nitride occurred through silicon oxynitride for the silica substrate and through aluminum oxynitride for both substrates

Growth of aluminum nitride on porous alumina and silica through separate saturated gas-solid reactions of trimethylaluminum and ammonia

Aluminum nitride-type species were prepared on porous alumina and silica by repeated separate, saturated reactions of gaseous trimethylaluminum (TMA) and ammonia with solid substrates. Reaction cycles of TMA at 423 K and ammonia at 823 K were performed up to six times. Growth per cycle was on average 2.4 AlN units/nm2, but it increased slightly with the number of reaction cycles. The amount of hydrogen present in NHx groups increased with the increasing number of reaction cycles. AlN4 units were observed by 27Al NMR on alumina, but the AlN remained amorphous to X-ray diffraction. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy revealed that the AlN-type species were spread out evenly on the surface of the particles. TMA reacted with equal probability with the still-exposed silica and the AlN-type species present on the surface, as shown by low-energy ion scattering. 29Si and 27Al NMR suggested that transition from the oxide substrates to aluminum nitride occurred through silicon oxynitride for the silica substrate and through aluminum oxynitride for both substrates

Depth profiling of Al2O3+ TiO2 nanolaminates by means of a time-of-flight energy spectromete

Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al2O3 + TiO2 nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20 nm and total thickness between 40 nm and 60 nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements 63Cu, 35Cl, 12C and 4He ions with energies ranging from 0.5 to 10 MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5 nm individual layer thickness.peerReviewe