Tunable SiO2 to SiOxCyH films by ozone assisted chemical vapor deposition from tetraethylorthosilicate and hexamethyldisilazane mixtures

Silica and silica-based materials with tunable functionalities are frequently encountered in low-k material applications, porous membranes, and microelectonic devices. In the present study, an innovative O2/O3 assisted CVD process for the deposition of such films at moderate temperature is presented, based on a dual precursor chemistry from hexamethyldisilazane (HMDS) and tetraethyl orthosilicate (TEOS). Films with tunable carbon content were obtained through variation of the HMDS flow ratio. A comprehensive FT-IR study reveals the transition of the material from a SiOxCyH type film containing -CH3 moieties, to a methyl-free SiOx film with the increase of the temperature. At the same time the water contact angle of 81.0° at 400°C is decreased to 52.8° at 550°C, related to the absence of methyl moieties in the latter. Ion beam analysis (IBA) confirms the lack of carbon in the films when deposition temperatures are equal to or exceed 500°C. The resistance to liquid corrosion is investigated as a function of the deposition temperature; SiOx type films present a low Pliskin etching rate of 15 Å.s-1, with this value increasing to 60 Å.s-1 for the SiOxCy:CH3 films produced at the lower temperatures. It is found that the addition of HMDS to a TEOS chemistry can be utilized to modulate the film composition from SiOx to SiOxCyH and by such, tune the film functional properties, in particular its etching rate, opening the way to the development of new sacrificial films

STEM nanoanalysis of Au/Pt/Ti-Si3N4 interfacial defects and reactions during local stress of SiGe HBTs

A new insight on the behavior of metal contact-insulating interfaces in SiGe heterojunction bipolar transistor is given by high-performance aberration-corrected scanning transmission electron microscopy (STEM) analysis tools equipped with sub-nanometric probe size. It is demonstrated that the presence of initial defects introduced during technological processes play a major role in the acceleration of degradation mechanisms of the structure during stress. A combination of energy-filtered transmission electron microscopy analysis with high angle annular dark field STEM and energy dispersive spectroscopy provides strong evidence that migration of Au-Pt from the metal contacts to Ti/Si3N4 interface is one of the precursors to species interdiffusion and reactions. High current densities and related local heating effects induce the evolution of the pure Ti initial layer into mixture layer composed of Ti, O, and N. Local contamination of Ti layers by fluorine atoms is also pointed out, as well as rupture of TiN thin barrier layer

Network hydration, ordering and composition interplay of chemical vapor deposited amorphous silica films from tetraethyl orthosilicate

The chemical or mechanical performance of amorphous SiO2 films depend on intrinsic physicochemical properties, which are intimately linked to atomic and molecular arrangements in the Si–O–Si network. In this context, the present work focuses on a comprehensive description of SiO2 films deposited from a well-established chemical vapor deposition process involving tetraethyl-orthosilicate, oxygen and ozone, and operating at atmospheric pressure in the range 400–550 °C. The connectivity of the silica network is improved with increasing the deposition temperature (Td) and this is attributed to the decreased content of hydrated species through dehydration-condensation mechanisms. In the same way, the critical load of delamination increases with increasing Td thanks to the silicon substrate oxidation. The utilization of a O2/O3 oxidizing atmosphere involving the oxidation of intermediates species by O2, O3 and O., allows increasing the deposition rate at moderate temperatures, while minimizing carbon, H2O and silanol contents to extremely low values (4.5 at.% of H). The SiOx stoichiometry and Td interplay reveals two distinct behaviors before and above 450 °C. The best corrosion resistance of these films to standard P-etching test is obtained for the minimum silanol content and the best network molecular ordering, with an etching rate of 4.0 ± 0.1 Å/s at pH = 1.5. The elastic modulus and hardness of the films remain stable in the investigated range of deposition temperature, at 64.2 ± 1.7 and 7.4 ± 0.3 GPa respectively, thanks to the low content in silanol groups

On the coupling between precipitation and plastic deformation in relation with friction stir welding of AA2024 T3 aluminium alloy

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Atomic scale characterization of deformation induced interfacial mixing in a Cu/V nanocomposite wire

International audienceThe microstructure of a Cu/V nanocomposite wire processed by cold drawing was investigated by high resolution transmission electron microscopy and atom probe tomography. The experimental data clearly reveal some deformation induced interfacial mixing where the vanadium filaments are nanoscaled. The mixed layer is a 2nm wide vanadium gradient in the fcc Cu phase. This mechanical mixing leads to the local fragmentation and dissolution of the filaments and to the formation of vanadium super saturated solid solutions in fcc Cu

Friction stir diffusion bonding of dissimilar metals

International audienceThis paper reports on a new method based on the friction stir welding process to join dissimilar metals in butt joint configuration. Two different systems were considered: AA1050 H16 aluminium/ASTM A284 steel and AA1050 H16/UNS C12200 H01 copper. The unthreaded steel tool pin was positioned in the aluminium plate so that it was tangential to the opposing metal. Bonding was accompanied by interfacial chemical reactions with no significant mechanical mixing. This new solid state welding process is called friction stir diffusion bonding. Room temperature cross-weld tensile strengths up to 82 MPa were obtained for both metal combinations. Microstructure characterisation suggested that higher joint strengths were associated with thinner, <1 μm thick intermetallic reaction layers at joint interfaces

Interfacial Reaction during Friction Stir Welding of Al and Cu

International audienceCommercially pure copper was joined to a 1050 aluminum alloy by friction stir welding. A specific configuration where the tool pin was fully located in the aluminum plate was chosen. In such a situation, there is no mechanical mixing between the two materials, but frictional heating gives rise to a significant thermally activated interdiffusion at the copper/aluminum interface. This gives rise to the formation of defect-free joints where the bonding is achieved by a very thin intermetallic layer at the Cu/Al interface. Nanoscaled grains within this bonding layer were characterized using transmission electron microscopy (TEM). Two phases were identified, namely, Al2Cu and Al4Cu9 phases. The nucleation and growth of these two phases are discussed and compared to the standard reactive interdiffusion reactions between Cu and Al

Complementary use of TEM and APT for the investigation of steels nanostructured by severe plastic deformation

International audienceThe properties of bulk nanostructured materials are often controlled by atomic scale features like segregation along defects or composition gradients. Here we discuss about the complimentary use of TEM and APT to obtain a full description of nanostructures. The advantages and limitations of both techniques are highlighted on the basis of experimental data collected in severely deformed steels with a special emphasis on carbon spatial distribution