Aluminum etchants

Figure 1 A. AFM images (tapping mode) of a sapphire surface before it was annealed in the tube furnace. The image is 5.0 pm x 5.0 pm, with units on the vertical cross sections in nm. B. AFM image of sapphire after it was annealed and etched in Aluminum Etchant A The image is 1.0pm x TO pm, units on the vertical cross section are in nm.

Aluminum Etchant A is an acid cocktail consisting of phosphoric, acetic, nitric, and water in the following ratios 16 1 1 2. Reference L.B. Goetting, T. Deng, and G.M. Whitesides, 1999,15, 1182. 

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... 

After removal of the native aluminum oxide layer, molecular chlorine (CI2) can etch pure, clean aluminum without a plasma (84,52), Indeed, CI2 may be the primary etchant species for aluminum in a glow discharge, perhaps due to a higher concentration of CI2 than chlorine atoms in the discharge (74). 

Fig. 2, Process steps used to produce the structure shown in Fig. 1 (a) A film of SiO > lias been formed by oxidizing the silicon and a layer of photoresist has been deposited on the SiCd (b) Shading shows a region of the photoresist that has been exposed to light and thereby made more soluble, (c) The exposed photoresist has been removed. (cl) An etchant that reacts with the SKF. but not with the photoresist, lias been removed, (e) Anodier solvent has been used to remove the unexposed photoresist, (f) Donor atoms have diffused into the silicon through the opening in the SiCr to produce an a-type region, fg) Additional masking steps, not shown, have permitted aluminum to be evaporated onto the diode in a pattern that forms a contact to the n region of the diode. (See Fig. 1 for legend)...

As indicated above, Mason et al. [13] found that the pretreatment affected the surface acidity of Ti-6,4. They found that surfaces treated with a basic etchant had an isoelectric point between 7.3 and 9.2. A phosphate-fluoride etch left the surface acidic with an isoelectric point between 5.4 and 7.3. As noted above, Finlayson and Shah [12] also found that the pretreatment affected the acidity of oxidized aluminum surfaces. 

Usually, dry etching of polyimide is performed by RIE with O2, CF, or their mixtures as an etchant gas, utilizing positive photoresist (2), metals such as aluminum (3), spin-on-glass (4), or SiN (5) as an etching mask. However, in the former case, it is difficult to define a fine via-hole as small as 2 pm or less because the resist thickness must be two or more times that of the polyimide as a result of the equal etching rates between photoresist and polyimide. In the latter case, though the fine pattern can be obtained the additional pattern transformation from the photoresist to the masking layer is necessary. 

Then the anodic alumina layer formed was removed chemically in the selective etchant composed of phosphoric (6 wt.%) and chromic (1.8 wt.%) acids at 60 C. Hemispheric etching pits - replica of the alumina cell bottoms - remain on the surface of the aluminum foil. The second porous anodization of aluminum was made. At this stage, the pores on the aluminum foil surface arise not in random way but at the sites of primary alumina cell Imprints to repeat the cell size. The pore diameter and spacing are dictated by the parameters of the anodization process, specifically by the electrolyte composition and the anodization voltage. The alumina film thickness is defined by the anodization time and the anodization current density. The second stage provides a continuous development of the alumina film. Total etching process takes 10-20h to get pores of approximately 100 pm lengths. 

Then the samples were rinsed in distillated water at 40 C with further rinsing in the running de-ionized water and drying at 90-95°C in an oven. The masking layer was removed from the back side and the rest of aluminum foil was etched in the etchant consisted of hydrochloric acid and copper chloride to get free-standing films of porous alumina. We found that the additional removal of alumina bottoms in pores can be reasonable to get hollow cylindrical pores throughout the sample. 

Tetramethyl Ammonium Hydroxide (TMAH). TMAH, (CH3)4NOH, etchant has been developed more recently for anisotropic etching of silicon. It is relatively safe to use and presents no special disposal issues. It has a very low oxide etch rate and does not attack aluminum if the soluhon contains a certain amount of silicates. However, hillocks tends to develop in this solution. ... 

Wet chemical etching is also a commonly used process to pattern the metallic film structure. In these cases, a suitable solvent for the metallic film is used to dissolve or etch away the exposed area of the metallic film. This wet etching technique has been used for various metallic films, such as gold, copper, aluminum, and others. However, there are cases where chemical etching of the metal can be difficult. For instance, the etching of the platinum film is not easy because of the required etchant for the platinum film. One of the patterning processes to overcome the potential... 

Plasma etchants are available for most of the films commonly used in micromachining. Etching of oxide, nitride, and silicon is usually done with fluorine-containing compounds such as SiF4, CF4, and SF6. Aluminum and other metals can be etched in chlorine plasmas such as SiC l4 and BC13. In certain conditions, better results can be obtained by combining several gases. 

Teflon and other fluorocarbon surfaces may be altered by chemical treatments using solvent solutions of sodium naphthalene complex or molten sodium. Teflon etchants, for example, Tetra-Etch , a tradename and product of W. L. Gore Associates, are effective in improving adhesion to Teflon. Oxidation treatments for metals such as copper or aluminum also produce highly polar oxide surfaces that are more easily bondable. The reader is referred to several sources for a more comprehensive... 

Uses Mfg. of acetic anhydride, cellulose acetate, vinyl acetate monomer acetic esters prod, of plastics, pharmaceuticals, cosmetics, aroma chems., dyes, insecticides, photographic chemicals, food additives solvent reagent acidifier solvent for electronic materials etchant (semiconductor mfg.) aluminum brightener laundry sour boiler water additive coagulant for latex buffer in cosmetics buffer, acidifier in textile baths preservative, acidity regulator in foods flavor, solvent, vehicle in foods, pharmaceuticals color diluent sanitizing solutions for food contact... 

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