Effect of aluminum seed layer on the crystallographic texture and electromigration resistance of physical vapor deposited copper interconnect

Abstract

The effects of an Al underlayer with respect to texture control and electromigration (EM) resistance of Cu films are investigated in this study. The Al underlayer enhances the (111) texture of Cu films and the surface smoothness of the annealed Cu film. The same cubic crystal structure (face-centercd cubic) and small difference of the nearest interatomic distance of the (111) plane between Cu and Al result in the increase of the peak ratio I((111))/I-(200) of Cu films. The thicker the Al film, the more preferred the Cu (111) orientation. The resistivity of the Cu/AI bilayer film, which increases at about 0.2 mu Omega .cm per 1-nm-thick Al underlayer, is smaller than the reported value of single phase Cu(Al) solution. The EM resistance of Cu interconnects is also improved when the Al underlayer is present. The mean time to failure (MTF) of Cu interconnects with a 5-nm-thick Al underlayer is longer by one order of magnitude than that without an Al underlayer at 240 degreesC and 12 MA/cm(2).