Requirements for Chip Metallization

The metal lines connecting transistors or other components on a Si chip must meet many, partially conflicting, requirements. Below is a list, including some materials that do not meet the particular requirement very well.
Can you guess the winner?

Desired Property Materials not meeting requirement
Very good conductivity All but Ag, Cu
High eutectic temperature with Si
(> 800 oC would be good)		 Au, Pd, Al, Mg
Low diffusivity in Si Cu, Ni, Li
Low oxidation rate; stable oxide Refr. Metals, Mg, Fe, Cu, Ag
High melting point Al, Mg, Cu
Minimal interaction with Si substrate Pt, Pd, Rh, V, Ni , Mo, Cr (form silicides easily)
Minimal interaction with poly Si Same as above
No interaction with SiO2 Hf, Zr, Ti, Ta, Nb, V. Mg, Al
But must stick well to SiO2 ?
Must also comply with other substrates, e.g. TiN ? (see example for Al)
Chemical stability, especially in HF environments Fe, Co, Ni, Cu, Mg, Al
Easy structuring Pt, Pd, Ni, Co, Au
Electromigration resistant Al, Cu
.... and many more,...

The winner is: Aluminum (with <1% of Si and Cu added).
Al, in fact, is pretty bad - but all others are worse!
Presently (2001) a switch to Cu takes place (the better conductivity is definitely needed). The industry will pay several 109 Dollars to develop the new material technology and change the production facilities.
 

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go to 2.3.1 General Applications

go to 2.2.3 Non-Metals

go to Al Grain Structure on Different Substrates

© H. Föll (Advanced Materials B, part 1 - script)