Copper-based chips

Copper-based chips are semiconductor integrated circuits which use copper for interconnections in the metalization layer, the BEOL. Since copper is a better conductor than aluminium, chips using this technology can have smaller metal components, and use less energy to pass electricity through them. Together, these effects lead to higher-performance processors. They were first introduced by IBM, with assistance from Motorola, in 1997.

The transition from aluminium to copper required significant developments in fabrication techniques, including radically different methods for patterning the metal as well as the introduction of barrier metal layers to isolate the silicon from potentially damaging copper atoms.

Although some form of volatile copper compound has been known to exist since 1947, with more discovered as the century progressed, none were in industrial use, so copper could not be patterned by the previous techniques of photoresist masking and plasma etching that had been used with great success with aluminium. The inability to plasma etch copper called for a drastic rethinking of the metal patterning process and the result of this rethinking was a process referred to as an additive patterning, also known as a "Damascene" or "dual-Damascene" process by analogy to a traditional technique of metal inlaying.

In this process, the underlying silicon oxide insulating layer is patterned with open trenches where the conductor should be. A thick coating of copper that significantly overfills the trenches is deposited on the insulator, and chemical-mechanical planarization (CMP) is used to remove the copper (known as overburden) that extends above the top of the insulating layer. Copper sunken within the trenches of the insulating layer is not removed and becomes the patterned conductor. Damascene processes generally form and fill a single feature with copper per Damascene stage. Dual-Damascene processes generally form and fill two features with copper at once, e.g., a trench overlying a via may both be filled with a single copper deposition using dual-Damascene.

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