Aluminum masking

In one approach" " thin-film aluminum is vapor deposited or sputtered onto the silicon wafer and photoetched to form a mask to etch the vias. The vias are plasma etched using fluorine or a gaseous fluoride compound such as carbon tetrafluoride but etching is stopped short of going completely through the silicon. The aluminum mask is then removed and silicon dioxide is deposited over the entire wafer to isolate the silicon from subsequent deposition of copper. A tie layer of Ti/W is generally deposited prior to copper deposition. The vias are then filled with either a conductive... 

Another lamination approach is the bonding of a film of thermoplastic liquid crystal polymer (LCP) to glass. The LCP layer can be structured with microchannels dry etched in oxygen plasma using an aluminum mask. After removal of the aluminum mask, the LCP can be laminated onto glass, silicon, or a metal under pressures at temperatures around 260-270 °C [9]. Again, the temperature is too high for biomolecule pre-deposition. 

Reactive Ion Etching (RIE), Fig. 4 Mierranasking horn aluminum mask... 

The surface QDs are visible as small brighter dots on the micrograph, showing that in such a mesa there are still many QDs. Samples with openings in a metaUic mask were prepared in the following way polystyrene nanobeads with diameters of 300 nm were dispersed on the sample, on which 100-nm aluminum were then deposited. The removal of the beads thus leaves circular openings in the aluminum mask [47]. 

Destruction of the masking ligand by chemical reaction may be possible, as in the oxidation of EDTA in acid solutions by permanganate or another strong oxidizing agent. Hydrogen peroxide and Cu(II) ion destroy the tartrate complex of aluminum. 

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

Ma.rine. In the presence of an electrolyte, eg, seawater, aluminum and steel form a galvanic cell and corrosion takes place at the interface. Because the aluminum superstmcture is bolted to the steel bulkhead in a lap joint, crevice corrosion is masked and may remain uimoticed until replacement is required. By using transition-joint strips cut from explosion-welded clads, the corrosion problem can be eliminated. Because the transition is metaHurgicaHy bonded, there is no crevice in which the electrolyte can act and galvanic action caimot take place. Steel corrosion is confined to external surfaces where it can be detected easily and corrected by simple wire bmshing and painting. 

Binder formulas for carpet backing, aluminum foil to paper, vinyl flooring, tire cord, paper labeling, masking tape, and oriented polypropylene tape applications are available from Midgley and Rea in Skiest [215]. 

Fig. 34. PAA aluminum surface covered with a thin layer of grease that masks the oxide morphology.

The enantioselective inverse electron-demand 1,3-dipolar cycloaddition reactions of nitrones with alkenes described so far were catalyzed by metal complexes that favor a monodentate coordination of the nitrone, such as boron and aluminum complexes. However, the glyoxylate-derived nitrone 36 favors a bidentate coordination to the catalyst. This nitrone is a very interesting substrate, since the products that are obtained from the reaction with alkenes are masked a-amino acids. One of the characteristics of nitrones such as 36, having an ester moiety in the a position, is the swift E/Z equilibrium at room temperature (Scheme 6.28). In the crystalline form nitrone 36 exists as the pure Z isomer, however, in solution nitrone 36 have been shown to exists as a mixture of the E and Z isomers. This equilibrium could however be shifted to the Z isomer in the presence of a Lewis acid [74]. 

Woodward s strychnine synthesis commences with a Fischer indole synthesis using phenylhydrazine (24) and acetoveratrone (25) as starting materials (see Scheme 2). In the presence of polyphosphor-ic acid, intermediates 24 and 25 combine to afford 2-veratrylindole (23) through the reaction processes illustrated in Scheme 2. With its a position suitably masked, 2-veratrylindole (23) reacts smoothly at the ft position with the Schiff base derived from the action of dimethylamine on formaldehyde to give intermediate 22 in 92% yield. TV-Methylation of the dimethylamino substituent in 22 with methyl iodide, followed by exposure of the resultant quaternary ammonium iodide to sodium cyanide in DMF, provides nitrile 26 in an overall yield of 97%. Condensation of 2-veratryl-tryptamine (20), the product of a lithium aluminum hydride reduction of nitrile 26, with ethyl glyoxylate (21) furnishes Schiff base 19 in a yield of 92%. 

Since double bonds may be considered as masked carbonyl, carboxyl or hydroxymethylene groups, depending on whether oxidative or reductive methods are applied after cleavage of the double bond, the addition products from (E)-2 and carbonyl compounds can be further transformed into a variety of chiral compounds. Thus, performing a second bromine/lithium exchange on compound 4, and subsequent protonation, afforded the olefin 5. Ozonolysis followed by reduction with lithium aluminum hydride gave (S)-l-phenyl-l,2-ethanediol in >98% ee. 

TV-aluminum imines are another example of masked inline derivatives of ammonia. They are easily synthesized by partial reduction of nitriles with diisobutylaluminum hydride (D1BAL-H)6. Addition of lithium organic reagents to /V-aluminum iniines 7 derived from O-protected cyanohydrins 6 provides a-amino alcohols 8a and 8b in moderate yields and low to good diastereo-selectivities n 12. 

The use of aluminum-based masks in photolithography has been proposed.347 According to the scheme employed, aluminum is deposited onto a polished glass sheet. The regions of the mask that should be light transparent are then converted into porous oxide. As the operation of aluminum anodization exhibits a much better vertical anisotropy than chemical etching, the masks obtained reproduce the parameters of standard masks more precisely than the chromium masks usually used. 

Both characteristic X-ray line and continuous spectra were used to evaluate the performances of the resists. To determine exposure parameters (i.e. sensitivity and contrast) irradiations were carried gut in this study using the aluminum Kot- 2 emission line at 8.3t A generated by means of a modified Vacuum Generators Limited model EG-2 electron beam evaporation gun. The resist samples were exposed through a mask (A) consisting of a range of aluminum foils of different thicknesses supported on an absorbing nickel frame in order to vary the X-ray flux. 

The polymers were dissolved in methylisobutylketone (MIBK) and spin-coated on oxjdized silicon wafers (1100 X thick Si02 layers) to form 5000 A thick films. After a prebaking to improve adhesion to the substrate, the resist samples were irradiated 0 through the mask (A) using the Al K 152 emission line at 8.3 A as X-ray source. The electron beam gun was operated at a 300 W power and the source to sample distance was U.9 cm. Taking into account the absorption of the aluminum foil mask,the different X-ray fluxes available on the sample were calculated from the relation given by (9) ... 

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