Capping a low resistivity
metal conductor line or via with a
refractory metal allows for effectively using chemical-mechanical
polishing techniques because the hard, reduced wear, properties of the
refractory metal do not scratch, corrode, or smear during chemical-mechanical
polishing. Conductive lines and vias are created using a combination of both
physical vapor deposition (e.g.,
evaporation or collimated
sputtering) of a low resistivity metal or
alloy followed by
chemical vapor deposition (CVD) of a
refractory metal and subsequent planarization. Altering a ratio of SiH4 to WF6 during application of the refractory metal cap by CVD allows for controlled incorporation of
silicon into the
tungsten capping layer. Collimated
sputtering allows for creating a refractory metal liner in an opening in a
dielectric which is suitable as a
diffusion barrier to
copper based metalizations as well as CVD
tungsten. Ideally, for faster diffusing metals like
copper, liners are created by a
two step collimated
sputtering process wherein a first layer is deposited under relatively
low vacuum pressure where directional deposition dominates (e.g., below 1 mTorr) and a second layer is deposited under relatively high
vacuum pressure where scattering deposition dominates (e.g., above 1 mTorr). For
refractory metals like CVD
tungsten, the liner can be created in one step using collimated sputtering at higher vacuum pressures.