Compound wafers, etching

For production of micro-mechanic devices etching paths parallel to the wafer substrate surface are often required. Bromine trifluoride (BrF3) is used for this special kind of anisotropic etching. Because of the extreme reactivity of this compound, electrical excitation and plasma formation is not necessary. 

Aluminum is often used as an alloy with a few atomic % Si and/or Cu to reduce electromigration (Fig. 1). This alloy is difficult to etch because copper does not form readily volatile compounds [73]. Fleating of the wafer to some 200 °C and intense ion bombardment to sputter off involatile products are then necessary to effect etching. Residual chlorine remaining on the wafer after aluminum etching can be deleterious because it can promote corrosion, especially in Al-Cu alloys. Hence wafer rinsing with DI water is common. Dry passivation by exposure to a fluorocarbon plasma has... 

Molecular acids Fluorides, chlorides, bromides, sulfates, phosphates, nitrogen/oxygen compounds Etch chambers, diffusion furnaces, CVD processes, buffered oxide etch, wet benches using HCl, HF Forms haze crystals on reticles, wafers, and exposure tool optical elements, causes corrosion of A1 and Cu metal lines... 

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... 

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