Metals used for fabrication in ICs in each layer

Hi,
I would like to know which all metals are used in each routed layer while fabricating the ICs. As the power and ground nets are routed in the higher layers where the resistance is less, I guess different metals are used for different layers.
Can somebody please throw some light upon this matter.

Thanks in advance.:|

Either Al (for processes >≈ 180nm) or Cu (for smaller process sizes). Higher layers where the resistance is less are thicker.

Initially metalization was done using aluminum for all the layers. But aluminum suffers a serious problem of electromigration. Electromigration reduces the width of metal layers in high current density areas with the time which in turn reduces long term reliability of chip. Aluminum has small grain boundaries so electromigration can happens easily. Mixing copper can prevent electromigration up to some extent. But as the technology shrinks down so width of metal layers. This leads to high current densities which in turn causes electromigration in aluminium base metalization. This also cause increase in metal layer resistance. This will increase RC delay which limits speed. So in sub-micron technology copper is used as interconnect material. To get less less resistance layers can be made wider. Generally width of metal layers increases as we go up..