Dmitri Starodub

HfO2 and Al2O3 gate dielectrics on GaAs grown by atomic layer deposition

High-performance metal-oxide-semiconductor field effect transistors (MOSFETs) on III–V semiconductors have long proven elusive. High-permittivity (high-κ) gate dielectrics may enable their fabrication. We have studied hafnium oxide and aluminum oxide grown on gallium arsenide by atomic layer deposition. As-deposited films are continuous and predominantly amorphous. A native oxide remains intact underneath HfO2 during growth, while thinning occurs during Al2O3 deposition. Hydrofluoric acid etching prior to growth minimizes the final interlayer thickness. Thermal treatments at ∼600°C decompose arsenic oxides and remove interfacial oxygen. These observations explain the improved electrical quality and increased gate stack capacitance after thermal treatments.

Interface structure and thermal stability of epitaxial SrTiO3 thin films on Si (001)

We have used medium energy ion scattering, temperature programmed desorption, and atomic force microscopy to study the interface composition and thermal stability of epitaxial strontium titanate thin films grown by molecular-beam epitaxy on Si (001). The composition of the interface between the film and the substrate was found to be very sensitive to the recrystallization temperature used during growth, varying from a strontium silicate phase when the recrystallization temperature is low to a Ti-rich phase for a higher recrystallization temperature. The films are stable towards annealing in vacuum up to ∼550°C, where SrO desorption begins and the initially flat film starts to roughen. Significant film disintegration occurs at 850°C, and is accompanied by SiO and SrO desorption, pinhole formation, and finally titanium diffusion into the silicon bulk.

Effect of nitric oxide annealing on the interface trap density near the conduction bandedge of 4H–SiC at the oxide/(112̄0) 4H–SiC interface

Nitric oxide postoxidation anneal results in a significant decrease of defect state density (Dit) near the conduction bandedge of n-4H–SiC at the oxide/(1120) 4H–SiC interface. Comparison with measurements on the conventional (0001) Si-terminated face shows a similar interface state density following passivation. Medium energy ion scattering provides a quantitative measure of nitrogen incorporation at the SiO2/SiC interface.

SILICON OXIDE DECOMPOSITION AND DESORPTION DURING THE THERMAL OXIDATION OF SILICON

The thermal oxidation of silicon is normally considered to occur via two different routes. At higher O2 pressures and lower temperature SiO2(s) film growth occurs (passive oxidation), while at lower O2 pressures and higher temperature SiO(g) is desorbed in an etching process (active oxidation). We have measured the yield of SiO into the gas phase in a wide range of dry O2 pressures (10-7–10-5 Torr) and Si substrate temperatures (620–870°C) in the passive as well as the active oxidation regimes. A phase diagram for silicon oxidation in this pressure–temperature region is obtained. We have found evidence for small but measurable yields of SiO(g) desorbing from the nascent oxide film during the initial stages of passive oxidation, even when the oxide film continuously covers the surface. A sensitive method for detecting volatile products based on condensation of desorbed species is described.

Oxygen diffusion and reactions in Hf-based dielectrics

Oxygen transport in and reactions with thin hafnium oxide and hafnium silicate films have been investigated using medium energy ion scattering in combination with O218 isotopic tracing methods. Postgrowth oxidation of Hf-based films in an O218 atmosphere at 490–950°C results in O exchange in the film. The exchange rate is faster for pure hafnium oxides than for silicates. The amount of exchanged oxygen increases with temperature and is suppressed by the SiO2 component. Films annealed prior to oxygen isotope exposure show complex incorporation behavior, which may be attributed to grain boundary defects, and SiO2 phase segregation.

Ammonia pretreatment for high-κ dielectric growth on silicon

Thermal nitridation of H∕Si(100) surfaces with NH3 gas has been studied as a pretreatment for atomic layer deposition of Al2O3. The chemical nature of both the nitride interface and the Al2O3 growth was characterized using in situ transmission infrared spectroscopy and medium energy ion scattering. Nitride layers thicker than 3–4A provide an effective barrier against interfacial SiO2 formation and promote the nucleation of Al2O3 growth.

STRUCTURE, COMPOSITION AND ORDER AT INTERFACES OF CRYSTALLINE OXIDES AND OTHER HIGH-K MATERIALS ON SILICON

High-resolution medium energy ion scattering (MEIS) was used to investigate structure, composition and defects in amorphous and crystalline oxides, and their interface with silicon. Isotopic oxygen reactions were examined in several model high-κ systems, including Hf and Ce oxides, silicates and nitrided silicates as a function of composition, crystallinity and post-deposition annealing conditions. Our results show that for post-growth oxidation of Hf-based films there was extensive O exchange throughout the film which could be suppressed by the addition of SiO2. Under our growth conditions, there was no measurable interfacial SiO2 formation. In contrast Ce silicates exhibit rapid interface growth under similar oxygen exposures. Epitaxial SrTiO3 and Sc2O3 films grown by MBE on Si were studied in different channeling geometries. We show that diffusion of Ti and O during SrTiO3 film growth on Si (001) results in substitution of thin interfacial Sr

Thermal activation of As implanted in bulk Si and separation by implanted oxygen

We have studied arsenic (As) diffusion and its electrical activation in two different types of silicon substrates: bulk Si and separation by implanted oxygen (SIMOX) wafers. Both substrates were implanted with a dose of 5×1014cm−2 As+ at 20keV. The samples were annealed and physical characterization was performed with secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry, and medium energy ion scattering. The electrical properties of the film were extracted by Hall measurements. The SIMS results showed a lower dopant outdiffusion loss to the atmosphere during annealing in the SIMOX samples. The electrical results for the SIMOX samples were also superior to those of bulk Si due to the higher dopant retention, likely the result of a higher concentration of vacancies, which in turn increases the relative fraction of As which is activated (in substitutional sites). The net effect was a higher sheet carrier concentration and lower sheet resistance in the SIMOX samples. The implantation...