Oxide growth

During immersion in the FPL etch bath, the oxide film that is formed during the fabrication process, and some of the metal itself, are dissolved. The FPL oxide is grown during the etch and results from the balance of oxide formation and dissolution according to the reactions 

FIGURE 6. AES sputter depth-profiles of 2024 aluminum surface before and after an FPL etch. Multiplication factors Al x 1 Mg, Cu, Ca, C x 2 O x 0.25. (From Reference 9.) 

FIGURE 7. Cross-section micrograph of a CAA oxide after TAA pretreatment. Note the thick, porous, CAA-induced oxide under the thin, smooth, TAA oxide film. 

FIGURE 8. Schematic diagram of a wedge-crack propagation test for bond durability. 

FIGURE 9. AlOOH (boehmite) cornflake structure formed during the hydration of the aluminum adherend surface (a) stereo micrograph (b) isometric drawing. (From Reference 41.) 

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Figure C2.8.7. Principal oxide growth rate laws for low- and high-temperature oxidation inverse logarithmic, linear, paralinear and parabolic.

Sihcon dioxide properties depend on the techniques used for oxide growth. The index of refraction for dry oxides decreases when higher processing temperatures are used whereas the oxide density increases. 

Fig. 9. Fabrication sequence for an oxide-isolated -weU CMOS process, where is boron and X is arsenic. See text, (a) Formation of blanket pod oxide and Si N layer resist patterning (mask 1) ion implantation of channel stoppers (chanstop) (steps 1—3). (b) Growth of isolation field oxide removal of resist, Si N, and pod oxide growth of thin (<200 nm) Si02 gate oxide layer (steps 4—6). (c) Deposition and patterning of polysihcon gate formation of -source and drain (steps 7,8). (d) Deposition of thick Si02 blanket layer etch to form contact windows down to source, drain, and gate (step 9). (e) Metallisation of contact windows with W blanket deposition of Al patterning of metal (steps 10,11). The deposition of intermetal dielectric or final...

Electron tunnelling through the stable oxide film to the adsorbed oxygen which sets up a potential and causes ion drift, thus resulting in logarithmic oxide growth. 

Small additions of Ce have been shown to have a favourable influence on oxide growth of several Fe-Cr alloys by improving scale adherence and acting as nucleation sites for CrjO, . Levels of Ce as low as 0.024% reduce the carbon uptake of steels in carbonaceous atmospheres by several orders of magnitude. Trace concentrations of As and Sn have been found to improve the breakaway properties of mild and low alloy steels in CO/COj, whereas Cu has been found to be detrimental. ... 

Fig. 7.7 Oxide growth stresses on curved surfaces (after Hsueh and Evans...

A wide variety of in situ techniques are available for the study of anodic hhns. These include reflectance, eUipsometry, X-ray reflectivity, and SXRD. X-ray reflectivity can be used to study thick surface layers up to 1000 A. The reflectance technique has been used to study oxide growth on metals, and it yields information on oxide thickness, roughness, and stoichiometry. It the only technique that can give information on buried metal-oxide interfaces. It is also possible to get information on duplex or multiple-layer oxide hhns or oxide hhns consisting of layers with different porosity. Films with thicknesses of anywhere from 10 to 1000 A can be studied. XAS can be used to study the chemistry of dilute components such as Cr in passive oxide hhns. 

At room temperature and in the presence of oxygen the colloidal dispersion stabilized by glucose is less stable than the PVA stabilized ones owing to the slow glucose aerobic oxidation growth of particles from 2.7 to 3.5 nm has been observed in a few hours. 

Jerkiewicz G, Vatankhah G, Lessard J, Soriaga MP, Park YS. 2004. Surface-oxide growth at platinum electrodes in aqueous H2SO4 Reexamination of its mecharusm through combined cyclic-voltammetry, electrochemical quartz-crystal nanobalance, and Auger electron spectroscopy measurements. Electrochim Acta 49 1451-1459. 

Figure 9.6 Visual representation of the platinum oxide growth mechanism, (a) Interaction of H2O molecules with the Pt electrode occurring in the 0.27 V < < 0.85 V range, (b) Discharge of 5 ML of H2O molecules and formation of 5 ML of chemisorbed oxygen (Ochem)- (c) Discharge of the second ML of H2O molecules the process is accompanied by the development of repulsive interactions between (Pt-Pt) -Ofi m surface species that stimulate an interfacial place exchange of Ochem and Pt surface atoms, (d) Quasi-3D surface PtO lattice, comprising Pt and moieties, that forms through the place-exchange process. (Reproduced with permission...

Harrington DA. 1997. Simulation of anodic Pt oxide growth. J Electroanal Chem 420 101-109. 

Moreover, novel techniques of thin-film analysis (EXAFS, RBS, XPS, etc.) and improved sensitivity of traditional techniques (e.g., IR spectroscopy) have afforded a better understanding of anodic oxide growth and have even led to a reconsideration of commonly accepted concepts. 

A more detailed discussion of the problem, including some approximate solutions for the time dependence of oxide growth, is available in Ref. 46. 

The fact is that, on the one hand, a significant field strength, E9 is needed to provide significant current. On the other hand, once in the practical current density range between 0.1 and 10 mA/cm2, a relative insensitivity of the field to the current density is found. In fact, an inverse field of 1.3 to 1.8 nm/V is accepted in the literature as characteristic of the oxide growth, without mention of the current density used. 

In a number of works, a potentiostatic regime has been used for the experimental and theoretical study of the anodization of aluminum and other valve metals.80 Upon the application of a constant potential step, Va, barrier-forming electrolytes are characterized by a sharp increase in the anodic current to a certain maximum. Both the slope and the maximum are determined by the impedance of the cell circuit. Subsequently, there is a continuous decrease in the anodic current, which is due to oxide growth. The decay of the anodic current can be described by the expression81... 

In conclusion, one can say that most anodic oxide films are of a duplex, or even triplex, character, with only the inner portion being composed of a pure anhydrous oxide. In the duplex films, the outer layer contains anions and often a degree of hydration. There could exist a third thin oxide layer at the surface, again with somewhat different properties, which may have a role in the kinetics of oxide growth. 

Data on anion incorporation into a growing porous oxide were obtained Fukuda and Fukushima.165,166 Their study was the first to demonstrate a correlation between the kinetics of accumulation of oxalate165 or sulfate166 anions and the change of porous oxide growth stages. The results of galvanostatic and potentiostatic... 

Figure 31. Correlation of the kinetics of oxide growth with kinetics of sulfate incorporation into the oxide during galvanostatic (a) and potentio-static (b) anodization of A1 in Ff2S04 solutions.166...

When the results for oxide growth and anion incorporation172,160 are compared with the kinetics of space charge accumulation in barrier and porous alumina films [see Section IV(1)], it can be concluded that anion incorporation modifies the electrostatics of the external oxide interface, thus influencing oxide dissolution and pore formation.172... 

A number of researchers have assumed that oxide growth involves inward migration of OH- groups from the electrolyte and... 

The apparent large differences in the activation energy of hydration for oxides formed in acidic and alkaline solutions reflect the basic differences in the mechanism of oxide growth in these two cases. 

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