This 6-inch chip (top image) is made using under-bump metallization that puts solder onto intricately patterned surfaces to encapsulate the circuitry (magnification below). Photos courtesy Milara.
Subtractive process
Currently, the traditional method of semiconductor manufacture is a subtractive process. That is, successive layers of metal are first deposited on the wafer surface to create the multilayer electronic circuitry. With the patterning of each new surface the unwanted materials are removed by etching.
Only a small amount of the raw materials used in the process actually ends up in the final product. Chemical engineers have focused on reducing the waste by developing innovative ways to increase the recycling and reuse of raw materials.
Additive process
Newer additive processes that require fewer steps are also being designed. Manufacturers can selectively place metal, silicon, or other materials on the chip surface just where they are needed to create the desired circuitry. This method not only decreases the amount of materials required but also the amount of waste material produced during manufacturing.
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