Serge Rigo

DRY OXIDATION MECHANISMS OF THIN DIELECTRIC FILMS FORMED UNDER N2O USING ISOTOPIC TRACING METHODS

We investigated the mechanisms of thermal reoxidation in dry O2 of silicon oxynitride films prepared by processing Si(100) wafers in a rapid thermal furnace in a pure nitrous oxide (N2O) ambient, using isotopic tracing of oxygen and nitrogen. Standard nuclear reaction analyses for the measurement of the total amounts of the different isotopes, and very narrow resonant nuclear reactions for high resolution (1 nm) depth profiling of these elements were used. The silicon oxynitride films grown in pure 15N216O were 8‐nm thick, with a small amount of nitrogen localized near the interfacial region. Under reoxidation in dry 18O2, the thickness of the dielectric film increased while a pronounced isotopic exchange took place between the 18O from the gas and the 16O from the film, as well as a significant loss of 15N. This is in contrast with the reoxidation in dry O2 of pure SiO2 films, where the oxygen exchange is rather small as compared to that observed in the present case.

Incorporation of oxygen and nitrogen in ultrathin films of SiO2 annealed in NO

The areal densities of oxygen and nitrogen incorporated into ultrathin films of silicon dioxide during rapid thermal processing in nitric oxide, as well as the regions where these incorporations took place, were determined by combining nuclear reaction analysis and narrow nuclear resonance depth profiling with isotopic enrichment of the processing gas. Oxygen is seen to incorporate in the near-surface and near-interface regions of the oxynitride films, whereas nitrogen is incorporated only in the near-interface regions. The growth of the oxynitride film is very moderate as compared to that of a SiO2 film in dry O2. The thermal oxynitridation of ultrathin SiO2 films takes place by two mechanisms in parallel: the major part of the NO molecules, which react with the silica, decompose in the near-surface region, the O atoms being exchanged for O atoms preexistent in this region of the SiO2 films; a minor portion of the NO molecules diffuse through the silica film in interstitial sites, without reacting with i...

Diffusion of near surface defects during the thermal oxidation of silicon

The diffusion of defects during the thermal growth of SiO2 film on Si(100) in dry O2 was investigated using sequential treatments in natural oxygen (16O2) and in heavy oxygen (18O2) in a Joule effect furnace. The 18O depth profiles were measured with a depth resolution better than 1 nm, using the nuclear reaction narrow resonance 18O(p,α)15N (ER=151 keV, ΓR=100 eV). From these profiles, we confirmed that just below the surface an exchange between the oxygen atoms from the gas phase and those from the silica occurs, even for silica films thicker than 20 nm. This fact is not predicted by the Deal and Grove model. A diffusion of oxygen related defects takes place in the near surface region, with an apparent diffusion coefficient D*=4.33×10−19 cm2/s for an oxidation temperature of T=930 °C and for an oxygen pressure of P=100 mbar.

Formation of modified Si/SiO2 interfaces with intrinsic low defect concentrations

The modification by postoxidation NO treatments of the Si/SiO2 interface in thermally grown Si(100)/SiO2 layers has been studied by nuclear reaction analysis and electron paramagnetic resonance spectroscopy. Our results demonstrate a selective incorporation of NO molecules at the Si/SiO2 interface and a drastic reduction in the interface defect density. In this new configuration, the Pb center density, which is typically 2×1012 cm−2 in the as oxidized samples, is reduced to below 1011 cm−2 without any hydrogen passivation. The thermal treatment in NO atmospheres opens the perspective for the formation of hydrogen free low defect Si(100)/SiOxNy interfaces conserving the qualities of the SiO2 dielectric.

Isotopic tracing during rapid thermal growth of silicon oxynitride films on Si in O2, NH3, and N2O

We performed isotopic tracing of O, N, and H during rapid thermal growth of silicon oxynitride films on silicon in two different sequential, synergistic gas environments: O2, followed by NH3, then followed by N2O; and N2O, followed by NH3. Using nuclear reaction analysis and high resolution depth profiling, we demonstrate that the oxynitride films grow by means of thermally activated atomic transport involving the three traced species. Concomitantly, isotopic exchange processes take place. Growth in these sequential gas environments leads to oxynitride films with N concentration profiles and H concentrations different from those obtained by commonly used processes like thermal growth in N2O only or thermal nitridation of SiO2 films in NH3.

Nitrogen transport during rapid thermal growth of silicon oxynitride films in N2O

We investigated the transport of nitrogenous species during rapid thermal growth of silicon oxynitride films on Si in N2O, using N isotopic tracing and high resolution depth profiling techniques. The results indicate that the diffusion of nitrogenous species (most probably NO) through the growing oxynitride film to react with Si at the oxynitride/Si interface, induces the incorporation of N near this interface. This mechanism acts in parallel with a site‐to‐site jump mechanism (interstitialcy or vacancy) of diffusion and chemical reaction of nitrogenous species in the volume of the growing oxynitride film. The characteristic N accumulation only near the interface obtained by rapid thermal processing growth in N2O is due to the removal of N from the near surface region of the films, here attributed to atomic exchanges O↔N taking place during growth. Furthermore, N↔N exchange was also observed.

Time dependence of the oxygen exchange O2↔SiO2 at the SiO2–Si interface during dry thermal oxidation of silicon

During dry thermal oxidation of silicon oxygen exchange reactions may occur between oxygen molecules (O2↔O2, catalyzed by the SiO2) or between oxygen from the gas phase and the oxygen in SiO2 (O2↔SiO2), both at the surface and at the Si–SiO2 interface. We found that the oxygen exchange rate at the Si–SiO2 interface is at least 25% of the oxygen uptake rate, requiring the movement of oxygen both from the surface to the interface, and from the interface to the surface. The oxygen exchange at the interface is further evidence in favor of the presence of a reactive interfacial layer between the growing oxide and the silicon substrate.

Isotopic tracing of Si during thermal growth of Si3N4 ultrathin films

Abstract We investigated the mobility of Si atoms during the thermal growth of silicon nitride films in ammonia using Si isotopic labeling, together with nuclear resonant reaction analysis for depth profiling. A thin 29Si-enriched layer of silicon with nominal thickness of 1.4 nm was deposited on a Si(001) wafer with natural isotopic composition (92.2% 28Si, 4.7% 29Si). After epitaxial recrystallisation of the enriched layer, a Si3N4 film with nominal thickness of 2.86 nm was thermally grown in ammonia atmosphere. Excitation curves of the narrow resonance in the 29Si(p,γ)30P nuclear reaction at ER = 324 keV were measured using a high efficiency γ-ray detection system (solid angle around 4π). The very close similarity between the excitation curves obtained for two pieces of the same sample, one without and one with thermal nitridation led us to conclude that the Si atoms are not mobile during thermal growth.

IBA study of the growth mechanisms of very thin silicon oxide films: the effect of wafer cleaning

Abstract The growth mechanisms of very thin silicon oxide films formed during rapid thermal oxidation were studied using ion beam analysis and 18 O isotopic tracing methods. In this paper we report on the effects of different cleaning procedures of silicon wafers prior to oxidation in dry oxygen ( 16 O 2 followed by 18 O 2 ) on the growth mechanisms and kinetics. Typical oxide thicknesses ranging from 0.2 to 10 nm were studied. The 18 O and 16 O isotopic profiles were determined by ion beam analysis methods, namely: the 18 O(p, α ) 15 N narrow resonance at 151 keV, and the 18 O(p , α) 15 N and the 16 O(d, p) 17 O reactions associated with step-by-step chemical dissolution. The profiles could be related to current theories on the initial stages of thermal growth of silicon oxide layers allowing us to draw some conclusions regarding the role of surface cleaning of the silicon wafers on the formation of silicon fragments in the volume of the very thin oxide layer. The influence of rapid thermal processing parameters like temperature, time and oxygen partial pressure on the growth mechanisms were also studied and discussed here.

Thickness of the SiO2Si interface and composition of silicon oxide thin films: effect of wafer cleaning procedures

Abstract We determined the areal density of Si atoms constituting the oxide-silicon interface and the stoichiometry of ultra-thin silicon oxide films, thermally grown on Si(001) in dry 18 O 2 atmospheres, using the channeling of α-particles along the 〈001〉 axis of the Si substrates associated with grazing angle detection of the scattered particles. The amount of 18 O atoms in the films was determined independently using the 18 O(p,α) 15 N nuclear reaction at 730 keV. The Si wafers were submitted to different cleaning procedures before oxidation in 18 O 2 , namely: standard RCA cleaning, HF etching followed by a rinse in ethanol and rapid thermal cleaning (RTC) under high vacuum. The stoichiometry of all oxide films having thicknesses between 2 and 13 nm could be fitted assuming a ratio O Si = 2 , that is, the films were constituted by silicon dioxide. By comparing the results for samples cleaned in different ways, however, we noticed a pronounced change in the number of atoms in the non-registered Si layers at the SiO 2 Si interface and so in the thickness of these interfaces.