A by-product of dry etching metal is a thin film of organic material referred to as a polymer. The polymer is stripped away during photoresist removal (or by a separate cleaning step). Variations in etching conditions or etching time can increase the amount of polymer formed. Failure to remove the polymer results in increased, but very low leakage between metal lines. Additionally, chlorine involved in the metal etch chemistry may be held in the polymer. The trapped chlorine can cause metal corrosion when the wafers are exposed to air.
Example: Corrosion cotton balls
Optical inspection detected abnormalities along edges of aluminum metal strips.
SEM examination confirms globular shaped abnormalities along edges of metal 2. See Fig. (1).
After removal of passivation, smaller, white material remains. This material, a corrosion by-product, is a growth from the exposed side of metal. See Fig. (2). Aluminum consumption is often detectable at larger sites.
Figure (1). SEM image of abnormalities associated with edges of metal lines.
Figure (2). After passivation removal, bright material exists on the edges of metal 2.
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