Plasma Etching of Aluminum

Chlorine-based plasma etching of aluminum films causes serious degradation of photoresist materials. To some extent, these effects are a result of the etch product, AICI3. Aluminum trichloride is a Lewis acid used extensively as a Friedel-Crafts catalyst. Therefore, it is hardly surprising that this material reacts with and severely degrades photoresists (74). 

C.J. Tracy and R. Mattox, "Mask considerations in the plasma etching of aluminum," Solid State Technol. 25 6, 83 (1982)... 

It is well known that ionic contaminations on the surface of electronic components impair their functioning [221,222]. Corrosion of aluminum after etching, for example, is regarded to be one of the major problems in the dry, chlorine gas-based plasma etching of aluminum. 

Initial studies of the dry-etch resistance of these resists showed that PFEMA had an etching rate in a CCl plasma (p = 0.2 torr, P = 600 W) about threeotimes lower (i.e. 380 X/min) than that of aluminum (i.e. 1200 A/min). 

It is always interesting to know the fate of the Fe species remaining on the surface. For the W plug application, after W CMP, the subsequent relevant processes are the deposition, patterning and etch of the Ti-Al (aluminum)-TiN stack. The Fe residuals on the surface will not cause any problem for the metal deposition because the entire surface is covered by metals. However, a problem may occur in the metal etch process because the BCI3 plasma chemistry can not etch away Fe. The reaction products between Fe and BCI3 are FeCl complexes, which are nonvolatile [22]. They... 

Bauer S, Wolfe I, Wemer N, et al. 1992. Toxicological investigations in the semiconductor industry 1. Studies on the acute oral toxicity of a complex mixture of waste products from the aluminum plasma etching process. Toxicol Ind Health 8 141-156. 

Corrosion. Aluminum is a not a noble metal and is attacked by both alkali and acidic solutions. Because of the presence of a surface A1203 film, the metal is protected against corrosion [Diggle et al.136, Borgmann et al.137]. This oxide film, however, is easily penetrated, for instance, by the presence of chlorine ions which remain in the resist after a chlorine based plasma etch. Also, the presence of Cu in the aluminum weakens the corrosion resistance of the alloy by the presence of an unfavorable electrochemical couple (A1/Cu2+). 

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. 

In plasma etchers, specific radicals are selected from the mix of the species generated within the chamber to effect the etching action. For the specific case of species generated from CF4 gas within a plasma chamber, for example, the fluorine radical (F) is selected by means of an appropriately configured perforated aluminum shield or other contraption that blocks the other species from reaching the wafer. In this way, etching of the wafer proceeds only by the reaction of the fluorine radical. Substrates such as silicon, silicon dioxide, and silicon nitride are readily etched by this technique. ... 

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. 

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