Atomic layer deposition (ALD) of amorphous titanium dioxide (TiO 2 ) at 100 °C using the precursors titanium tetrachloride (TiCl 4 ) and water (H 2 O) was studied on two different surfaces by in situ X-ray photoelectron spectroscopy (XPS). The initial growth rate on hydroxyl-enriched silicon dioxide (SiO 2 ) is found to be higher than on hydrogen-terminated silicon. Moreover, the data show that the growth rate is accelerated during the first several ALD cycles on both surfaces. The interface between the SiO 2 substrate and TiO 2 is abrupt and composed of Si-O-Ti bonds. On the hydrogen-terminated silicon surface, the XPS results provide evidence of direct Si-Ti bond formation without traces of interfacial oxide. However, a silicon oxide layer forms on this surface after vacuum annealing, concurrent with the reduction of TiO 2 , suggesting that the TiO 2 film is the oxygen source for the silicon oxidation under these conditions. Chlorine incorporates into the TiO 2 films on both surfaces and is found to concentrate near the Si/TiO 2 interface.
We have studied the atomic layer deposition (ALD) of ruthenium using bis(2,4-dimethylpentadienyl) ruthenium and oxygen. We show that the process is achievable at a low operating temperature of 185 C. Variation in the exposure time and pressure of the oxygen counterreactant has significant effects on the nucleation, growth rate and composition of the deposited ruthenium films. High oxygen pressure helps to promote the nucleation of ruthenium on a silicon dioxide substrate. Although saturation conditions are achieved with the Ru precursor, saturation of the ruthenium growth rate with oxygen exposure is observed only for a small range of oxygen exposure. Increasing the oxygen exposure further results in the incorporation of oxygen in the deposited film to form ruthenium oxide, a process which is enhanced at higher deposition temperature. We propose that the slow diffusion of oxygen to the subsurface region is a rate-limiting step in this process. We demonstrate that the composition of the deposited films from metallic ruthenium to ruthenium oxide, as well as the average grain size, may be regulated by tuning the pressure and exposure time of the oxygen counterreactant. Hence, this low temperature ALD process provides a flexible route to the deposition of Ru-based films.
The mechanism of platinum atomic layer deposition using (methylcyclopentadienyl)trimethylplatinum and oxygen is investigated with in vacuo photoemission spectroscopy at the Stanford Synchrotron Radiation Lightsource. With this surface-sensitive technique, the surface species following the Pt precursor half cycle and the oxygen counter-reactant half cycle can be directly measured. We observed significant amounts of carbonaceous species following the Pt precursor pulse, consistent with dehydrogenation of the precursor ligands. Significantly more carbon is observed when deposition is carried out in the thermal decomposition temperature region. The carbonaceous layer is removed during the oxygen counter reactant pulse, and the photoemission spectrum shows that a layer of adsorbed oxygen remains on the surface as previously predicted.
The structural properties of Pt films grown by atomic layer deposition (ALD) are investigated with synchrotron based x-ray scattering and x-ray diffraction techniques. Using grazing incidence small angle scattering, we measure the lateral growth rate of the Pt islands to be 1.0 Å/cycle. High resolution x-ray diffraction reveals that the in-plane strain of the Pt lattice undergoes a transition from compressive strain to tensile strain when the individual islands coalescence into a continuous film. This transition to tensile strain is attributed to the lateral expansion that occurs when neighboring islands merge to reduce their surface energy. Using 2D grazing incidence x-ray diffraction, we show that the lattice orientation becomes more (111) oriented during deposition, with a sharp transition occurring during coalescence. Pt ALD performed at a lower deposition temperature (250 °C) is shown to result in significantly more randomly oriented grains.
The crystal structure and growth behavior of Ru and RuO 2 on amorphous SiO 2 are measured during atomic layer deposition (ALD) by ex situ and in situ high-resolution synchrotron radiation X-ray diffraction (XRD). In situ XRD studies suggest that RuO 2 films grown by bis(2,4dimethylpentadienyl)ruthenium, Ru(DMPD) 2 , and oxygen at low temperature do not initially nucleate as RuO 2 . Despite large oxygen exposures during the ALD process, the initial nuclei form as hcp Ru. Then, after higher numbers of ALD cycles, crystalline rutile RuO 2 begins to appear. The results suggest that a critical Ru nucleus size is required to initiate the growth of RuO 2 . We speculate that a rate limiting step in the oxidation of Ru, possibly the formation of subsurface oxygen, is dependent upon the size of the Ru nuclei. Although the hcp Ru films are textured with a (002) preference in the growth direction, the rutile RuO 2 films once they nucleate have no preferential orientation.
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