Diffusion barrier layer

There are various theories on how passive films are formed however, there are two commonly accepted theories. One theory is called the oxide film theory and states that the passive film is a diffusion-barrier layer of reaction products (i.e., metal oxides or other compounds). The barriers separate the metal from the hostile environment and thereby slow the rate of reaction. Another theory is the adsorption theory of passivity. This states that the film is simply adsorbed gas that forms a barrier to diffusion of metal ions from the substrata. 

The interconnecting holes are narrow and deep (at times less than 0.25 im wide and up to 2 im or more in depth) and, after a diffusion-barrier layer is applied, it must be filled completely with a high-conductivity metal (usually aluminum or tungsten) to provide the low-resi stance plug for inter-layer connections. Typically, CVD provides better step coverage and conformity than sputtering and other physical-vapor deposition processes. 

Franco T, HoshiarDin Z, Szabo P, Lang M, and Schiller G. Plasma sprayed diffusion barrier layers based on doped perovskite-type LaCr03 at substrate-anode interface in solid oxide fuel cells. J. Fuel Cell Sci. Technol. 2007 4 406-412. 

In electronic applications, where it is common to deposit copper and/or copper alloy and tin in sequence, with a nickel diffusion barrier layer, 0.5 fim thick, between the layers present, no failure occurs. Without the nickel layers between bronze/-copper/tin layers themselves, for instance, intermetaUic brittle layer(s) and Kirkendall voids are formed, leading eventually to separation of the coated system and substrate. 

Figure 9.8 SNMS depth profile of the matrix components of a barium strontium titanite (BST) perovskite layer on Si with a Pt/Ti02/Si02 diffusion barrier layer measured using SIMSLAB 410 (FISONS Scientific, iOkeV, Ar+ primary ions). (]. S. Becker and H. ]. Dietze, Int. /. Mass Spectrom. Ion Proc. 197, 1(2000). Reproduced by permission of Elsevier.)...

The relative contribution of these two processes is controlled by the average pore size. It is therefore possible to optimize the temperature sensitivity by the judicious choice of the porosity of the diffusion barrier layer (Vacek et al., 1986). The temperature coefficient of the sensor with 0.1-0.2 pm average pore diameter is 0.04%/°C between 640°C and 800°C. 

Koike J, Wada M. Self-forming diffusion barrier layer in Cu-Mn alloy metallization. Appl Phys Lett 2005 87(4)... 

As mentioned previously, we include reports and discussions of CVD processes for metallic electrodes and diffusion barrier layers. The diffusion barrier layer is interposed between the electrode and poly-Si plug to prevent chemical reaction between them. It becomes quite clear that all these CVD processes should be developed simultaneously because of the structural complexity of capacitors and process integration requirements. 

One method to achieve this goal is to deposit very thin metal electrodes just to form the interfacial potential barrier and then deposit the diffusion barrier layer with the necessary thickness. These two factors make a CVD process for barrier layer necessary. 

Partially coated monolith with diffusion barrier layer... 

The effect of a diffusion barrier layer on combustor performance is evident in the model calculations shown in Fig. 8. Temperatures at the monolith inlet are dramatically lower than those presented for the... 

Fig. 8 Axial temperature and methane conversion distributions in a catalytic combustor with alternate channels coated and a diffusion barrier layer deposited on top of the wash-coat. The thickness of the diffusion barrier layer decreases exponentially downstream from the inlet. Thirty percent of the total gas flow passes through catalytic channels. Curves are calculated solving Eqs. (1), (2), and (5) for the conditions presented in Table 1, after substituting Eq. (7) in the heat balance Eq. (5). Gas and wall temperatures are close to those in Figure 7 except for the inlet wall temperature, which is much lower now because the diffusion barrier layer limits the diffusion rate of methane to the washcoat. (View this art in color at www.dekker.com.)...

Diffusion barrier layers are an integral part of the fabrication of copper interconnects (Figs. 3 and 4). Barrier films isolate (encapsulate) Cu interconnects from adjacent dielectric materials. The diffusion barriers most studied to date are Ti, and TiN. ... 

Capping diffusion barrier layer Electroless plating... 

Osaka T et al (2002) Electroless nickel ternary aUoy deposition on SiO for application to diffusion barrier layer in copper interconnect technology. J Electrochem Soc 149 C573-C578... 

Yoshino M et al (2006) Fabrication of the electroless NiMoB films as a diffusion barrier layer on the low-k substrate. ECS Trans 1 57-67... 

For the rich or lean A characteristic, plugging of the diffusion barrier leads to a decreasing pumping current, which rotates the characteristic curve around A= 1. In contrast to this, cracks and delamination within the diffusion barrier layers lead to an increased pumping current causing an opposite rotation of the characteristic curve. 

Coating substrates with other C-diffusion barrier layers has also been attempted. A 25 nm thick film of TiN coated on a Fe substrate was found to be sufficient to prevent soot from formation on the Fe substrate and to inhibit C diffusion into the Fe substrate,... 

Recently, Kelner and co-workers [2] obtained a specific ohmic contact resistance of 3.5 x 10 6Qcm2 with a carrier concentration of 4x 10l8cm 3 to 6H-SiC. The contacts were resistively evaporated nickel that was rapidly thermally annealed at 1000°C, for 30 s, in a forming gas atmosphere. Crofton et al [3] recently reported a contact resistance as low as 10 5Qcm2 to p-type SiC. Another problem to be solved is the fabrication of low resistivity Au or Al overlays for device interconnects. These overlays have to be separated from contacts by a diffusion barrier layer (for example, W, Cr, Ti, or conducting nitrides). 

The main commercial use of solid SiO is as a vapor-deposition material for the production of SiOx thin films for optical or electronic applications (antireflective coatings, interference filters, beam-splitters, decorative coatings, dielectric layers, isolation layers, electrodes, thin-film capacitors, thin-film transistors, etc.), for diffusion barrier layers on polymer foils or for surface protection layers.Other uses for SiO have been proposed, such as the substitution of elemental silicon in the Muller-Rochow process for the production of organosilicon halides, because solid SiO can be produced at lower temperatures than elemental silicon. 

Second, a diffusion barrier layer is usually required to prevent intermetallic diffusion between the Pd alloy fllm and the stainless steel support. A strategy used by Pall Corporation to mitigate both of these issues is to deposit an oxide coating on the stainless steel Alter as shown in Fig. 12.4. This creates a diffusion barrier and reduces the surface roughness of the substrate. 

The long-term thermal stability between 350 and 450°C for a composite Pd porous stainless steel membrane with an oxide intermetallic diffusion barrier layer is shown in Fig. 13.7. As shown in the figure, the membrane showed no sign of deterioration after over 6,000 h of continuous testing. 

The thermal postprocessing could lead to a doping of the TiOj layers with aluminum from the electrodes due to the absence of a diffusion barrier layer. But since similar results could be observed for reactive ion beam sputtered titanium dioxide layers (without thermal postprocessing), this influence is insignificant. 

There are two commonly expressed points of view regarding the composition and structure of the passive film. The first holds that the passive film (Definition 1 or 2) is always a diffusion-barrier layer of reaction products—for example, metal oxide or other compound that separates metal from its environment and that decreases the reaction rate. This theory is sometimes referred to as the oxide-film theory. 

Hydrous ferrous oxide (Fe0 nH20) or ferrous hydroxide [Fe(OH)2] composes the diffusion-barrier layer next to the iron surface through which O2 must diffuse. The pH of saturated Fe(OH)2 is about 9.5, so that the surface of iron corroding in aerated pure water is always alkaline. The color of Fe(OH)2, although white when the substance is pure, is normally green to greenish black because of incipient oxidation by air. At the outer surface of the oxide film, access to dissolved oxygen converts ferrous oxide to hydrous ferric oxide or ferric hydroxide, in accord with... 

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