Oxidation etchant

The combination of a positive charge and reducibility of tetrazolium salts finds use as anticorrosion agents for metals.634,635 The y are components of an oxidant/etchant bath composition for silicon dioxide corrosion-resistant surfaces.636 They are also used as antistatic agents in polyamide... 

Kim, Y.-K. Kim, G T. Ha, J. S. 2007. Simple patterning via adhesion between a buffered-oxide etchant-treated PDMS stamp and a Si02 substrate Adv. Fund. Mater. 17 2125-2132. 

FIGURE 5.4. Current-potential curve obtained for (a) p-type silicon (0.075-0.125 2cm) and (b) p-type silicon (4-6Qcm) in oxide etchant at a dilution of 0.05 in 6.5% HF + 35% NH4F. (Reprinted from Eddowes. 1980, with permission from Elsevier Science.)... 

K. K. Yoneshige, H. G. Parks, S. Raghavan, J. B. Hiskey, and P. J. Resnick, Deposition of copper from a buffered oxide etchant onto silicon wafers, J. Electrochem. Soc. 142, 671, 1995. 

Etching in buffered oxide etchant (BOE) and in-situ replacement of the etchant... 

BOE . [General CheiiL] Ammonium flumide or hydrofluoric acid blends buffered oxide etchants. 

Nitric acid can also be used as the oxidizing agent. Nitric acid with HF is used to oxidize/etch surfaces such as silicon. Nitric acid together with an oxide etchant such as HF or ammonium bifluoride can be used to simultaneously oxidize and etch oxidizable material such as the silicon in aluminum alloys. 

Most molded plastics have a very smooth, hydrophobic surface that must be modified. Chemical etchants are used to oxidize and roughen the surface. The resultant hydrophilic surface promotes good metal-to-plastic adhesion. The etchant is usually a solution of chromic acid and sulfuric acid pure chromic acid can also be used. 

Many types of chemical treatment are used in industry. Chromic, permanganic, sulphuric, and chlorosul-phonic acids are often used as the oxidants. It has been shown that the adhesion of polyethylene to substrates, such as cellophane, steel, aluminium, and epoxy adhesives, improves upon pretreatment with any of the etchants mentioned previously. 

Nearly all aluminum parts are first treated in an alkaline solution. In some cases, this is only a cleaner for removing grease and soils sometimes it is a mild etchant to remove a layer of metal and its oxides. Frequently, this is all the surface preparation that is necessary. Any further preparation... 

Alkaline etchants are anisotropic. The etch rate for the (111) crystal planes of the Si crystal is smaller by about two orders of magnitude than the etch rate of any other crystal plane. The etch rate ratio between other crystal planes like (100) and (110) depends on etchant concentration and temperature, but doesn t usually exceed a factor of two [Sa6]. Addition of oxidizing agents reduces the anisotropy. The etch rate of (100) Si and Si02 in KOH at different temperatures is shown in Fig. 2.2. 

Etchants for defect and junction delineation are usually composed of HF and an oxidizing agent such as HN03 [Dal, Gr4, Ka4, Nel], K2Cr207 [Se5] or Cr03 [Sil, Jel, Sc7, Ya4, Me5]. Alkaline solutions are rarely used for defect delineation [Mal2], An etch pit will form on a silicon surface if the dissolution rate is enhanced locally. Enhancement of the etch rate may occur for various reasons ... 

Microporous silicon is suitable for sacrificial layer applications because of its high etch rate ratio to bulk silicon, because it can be formed selectively, and because of the low temperatures required for oxidation. PS can be formed selectively if the substrate shows differently doped areas, as discussed in Section 4.5, or if a masking layer is used. Noble metal films can be used for masking as well as Si02, Si3N4 and SiC. Oxidation conditions are given in Section 7.6, while the etch rates of an etchant selective to PS are given in Fig. 2.5 b. 

Mass spectrometer studies of oxidant additions to fluoro- and chlorocarbon gases have demonstrated that the relative reactivity of atoms with unsaturate species in a glow discharge follows the sequence F -- O > Cl > Br (41), Of course, the most reactive species present will preferentially undergo saturation reactions that reduce polymer formation and that may increase halogen atom concentration. Ultimately, determination of the relative reactivity of the plasma species allows prediction of the primary atomic etchants in a plasma of specific composition. 

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