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Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride/water and the trimethyl aluminum/water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma–optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a “shower model” of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxide films were lower than the surface fractions calculated assuming RD, suggesting the occurrence of island growth. Island growth was confirmed with transmission electron microscopy (TEM) measurements, from which the island size and number of islands per unit surface area could also be estimated. The conclusion of island growth for the aluminum oxide deposition on hydrogen-terminated silicon contradicts earlier observations. In this work, physical aluminum oxide islands were observed in TEM after 15 ALD reaction cycles. Earlier, thicker aluminum oxide layers have been analyzed, where islands have not been observed because they have already coalesced to form a continuous film. The unreactivity of hydrogen-terminated silicon surface towards the ALD reactants, except for reactive defect areas, is proposed as the origin of island growth. Consequently, island growth can be regarded as “undesired surface-selective ALD.” [ABSTRACT FROM AUTHOR]

Abstract: Band engineered Si/O superlattices are promising channel materials for ultimately scaled complementary metal oxide semiconductor devices. Theoretical calculations have indicated that insertion of O monolayers into Si lattice creates anisotropy in the Si band structure with an enhanced carrier mobility in the channel direction. However, the experimental demonstration of such superlattices is not straightforward, as it requires processes for the deposition of a monolayer of O on Si, and to continue the Si epitaxy thereon. In this work, we investigate processes for the fabrication of Si/O superlattices using the chemical vapor deposition technique. Ozone is used for the O deposition with control of the deposited O content at the monolayer level. The SiH4 based Si deposition is performed at low temperatures (500°C–550°C) in order to obtain a confined O monolayer in the Si superlattice. Si deposited on O layer of 1.2 O monolayers is completely amorphous. This indicates that this O layer is extremely uniform as it prevents any epitaxial ordering with the substrate. Reducing the O content to 0.9 O monolayers in combination with a slower Si deposition favors epitaxial ordering of Si on O/Si. Finally a defect free Si epitaxy is demonstrated on the O monolayer. Such ordering of epitaxial Si on the O layer provides a promising outlook for the growth of superlattices. [Copyright &y& Elsevier]

The authors demonstrate high-performing n-channel transistors with a HfO2/TaN gate stack and a low thermal-budget process using solid-phase epitaxial regrowth of the source and drain junctions. The thinnest devices have an equivalent oxide thickness (EOT) of 8 Å, a leakage current of 1.5 A/cm² at VG = 1 V, a peak mobility of 190 cm²/V · s, and a drive-current of 815 μA/μm at an OFF-state current of 0.1 μA/μm for VDD = 1.2 V. Identical gate stacks processed with a 1000-°C spike anneal have a higher peak mobility at 275 cm²/V · s, but a 5-Å higher EOT and a reduced drive current at 610 μA/μm. The observed performance improvement for the low thermal-budget devices is shown to be mostly related to the lower EOT. The time-to-breakdown measurements indicate a maximum operating voltage of 1.6 V (1.2 V at 125 °C) for a ten-year lifetime, whereas positive-bias temperature-instability :measurements indicate a sufficient lifetime for operating voltages below 0.75 V. [ABSTRACT FROM AUTHOR]

Abstract: Numerous metal oxides have been studied worldwide as possible high-k gate dielectric candidates for MOS devices on alternative semiconductor materials (Ge, III/V compounds). We will discuss thermal and plasma-enhanced atomic layer deposition (ALD) of a few materials, HfO2 and Al2O3. We will spend some attention to characteristic features of the growth process and specific growth precursors as this is known to influence strongly the quality of the layer bulk as well as the interface. Detailed electrical characterization of MOS capacitors build on such dielectric layers, before and after forming gas anneals, shows that these interface modifications can lead to a marked decrease of the smaller interface state peaks close to the edges of the bandgap, whereas the larger mid-gap peaks are barely touched. The results of atomistic modeling of the oxidation of a GaAs surface help to understand the origin of these mid-gap electronic states, which are responsible for the apparent pinning of the Fermi level. [Copyright &y& Elsevier]

The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O 3 ) or oxygen (O 2 ) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH 4 ) at 500 °C. After O 3 exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH 4 reactants, allowing more time for surface diffusion. After O 2 exposure, the O atoms are present in the form of SiO x clusters. Regions of hydrogen-terminated Si remain present between the SiO x clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness. [ABSTRACT FROM AUTHOR]