Raija Matero

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.

Introducing atomic layer epitaxy for the deposition of optical thin films

Abstract Atomic layer epitaxy (ALE) is introduced for the preparation of dielectric multilayer structures for optical applications. Owing to the self-limiting growth process, arising from alternate saturating surface reactions, ALE possesses several features which make it an attractive technique for depositing optical thin films: simple and accurate thickness control, uniformity over large-area substrates, good reproducibility and straightforward scale-up. In the present work, ALE deposition of some basic optical components, i.e. antireflection and high-reflection coatings, neutral beam splitters and Fabry-Perot filters, is demonstrated using ZnS and Al 2 O 3 as high and low refractive index materials. The optical performance of the resulting components was examined by comparing the measured transmittance and reflectance spectra with those calculated for the ideal structures. In addition, other ALE processes which are of potential use in the preparation of optical dielectric multilayers are summarized briefly. The drawbacks of ALE are discussed as well.

Influence of atomic layer deposition parameters on the phase content of Ta2O5 films

Abstract Ta 2 O 5 films were grown in atomic layer deposition (ALD) process on barium borosilicate glass substrates in the temperature range of 300–400°C from TaCl 5 and H 2 O. The film crystallinity was modified by precursor dosing and substrate temperature. The films deposited at temperatures somewhat above 300°C were partly crystallized, showing XRD reflections of hexagonal δ-Ta 2 O 5 phase. The reflection intensities and film haziness demonstrated maxima at certain values of the TaCl 5 pulse length. The film growth rate initially decreased with the increase in the pulse length. After exceeding the TaCl 5 pulse length value corresponding to the maximum in the crystallinity, the Ta 2 O 5 growth rate was stabilized. The intermediate δ-Ta 2 O 5 was transformed into the conventional low-temperature orthorhombic β-Ta 2 O 5 upon raising the growth temperature above 325°C and increasing the TaCl 5 doses.

Atomic layer deposition of ZrO2 thin films using a new alkoxide precursor

Abstract Zirconium oxide thin films were grown by atomic layer deposition using a new type of Zr alkoxide: [Zr(O t Bu) 2 (dmae) 2 ] 2 (dmae is dimethylaminoethoxide). Water was used as the oxygen source. The films grown at 190–240 °C were amorphous, and the films grown at 290–340 °C were nanocrystalline. The highest refractive index of the films was 2.08 at a wavelength of 580 nm. The permittivity of a film grown at 240 °C was 25.

Nickel suicide for source-drain contacts from ALD NiO films

In this work, we demonstrate the preparation of nickel monosilicide (NiSi) layers on silicon using a conformal NiO ALD process and thin sacrificial Ge interlayers. The interlayers protect the underlying Si from oxidizing during the NiO growth, while allowing for Ni diffusion during a silicidation anneal. The NiSi layers prepared have low amounts of impurities and near bulk resistivities, therefore making the processes promising candidates for applications in advanced semiconductor devices where high quality NiSi layers are needed, such as source-drain contacts. Good step coverage provided by ALD enables their use for example in non-planar transistors such as FinFETs and other multi-gate transistors with complex topographies.

Demonstration of Phase Change Memories devices using Ge 2 Sb 2 Te 5 films deposited by Atomic Layer Deposition

Phase change memory technology is considered as one of the most promising resistive memory solution. One issue, however, is the high electrical current required to reset the information. Indeed large energies are mandatory for amorphization of the crystalline phase change material. It has been demonstrated that energies can be highly decreased by reduction of the active volume and confinement of the phase change material. To do so, phase change materials deposition route with high filling capacity is needed. Atomic Layer Deposition (ALD) is well known for its high conformity. However, such a process is still a challenge for phase change materials such as GexSbyTez (GST). In this work, (i) ALD GST films are processed and characterized and (ii) realisation of phase change memory devices using ALD GST is demonstrated on 200mm wafers.

Studies on the Surface Reactions of Substituted Disilanes with Silica Surface

Both CVD and ALD deposition techniques benefit from a detailed understanding of the reaction mechanisms of the precursor molecules with the surface. In this paper, the reactions of hexakis ethylaminodisilane (AHEAD™), hexamethoxydisilane and hexamethyldisilane were studied on high surface area silica granules at 200-375 °C. Silica was heat treated at 200-820 °C to control the number of surface Si-OH groups. The samples were characterized by FTIR and solid state NMR spectroscopy. After the chemisorption of the precursors with silica, Si-H bonds, not originally present in the molecules, were identified for AHEAD and hexamethoxydisilane, but not for hexamethyldisilane. It is suggested that with AHEAD and hexamethoxydisilane, cleavage of the Si-Si bond takes place during the chemisorption with Si-OH sites. Since no reaction for hexamethyldisilane at the studied temperatures was observed, a prerequisite for the reaction with Si-OH groups seems to be the presence of electronegative O or N atoms in the ligands. In the paper, possible reaction mechanisms with the various surface species are discussed.