|The Damascene technique
By: Sverre Sjøthun, March 23, 2001 Print this article
A few years before those events, a small team of IBM engineers had invented a key technology for patterning thin films of metals, including copper. Called damascene in reference to the metallurgists of old Damascus who produced the finest polished swords in the medieval world, the technique was initially used to form "vias" - the small metal plugs that link separate layers of wiring in chips. In conventional deposition, a layer of metal and a layer of a masking material called photoresist are deposited on a silicon wafer.
Unwanted metal is then etched away with an appropriate chemical, leaving the desired pattern of wires or vias. Next, the spaces between the wires or vias are filled with silicon dioxide (an insulator), and finally the entire wafer surface is polished to remove excess insulator. Damascene patterning involves the same number of steps, but reverses the order of deposition. Etching the oxide first forms the pattern of wires or vias. The metal is deposited second, and the excess is removed by polishing. In both conventional and damascene patterning the process is repeated many times to form the alternating layers of wires and vias which form the complete wiring system of a silicon chip.
In the early 1980s, IBM's 4-megabit DRAM program combined the wire and via damascene process into so-called dual-damascene technology. This process is regarded as one of the critical advances and key enablers in the development of copper technology. The fact that IBM had years of experience in such processing gave the company a significant leg up on the way to copper
Paving the road for a new generation of processors
The Damascene technique
The Damascene technique continued; Dual Damascene
What does the future hold?