wafer bonding/fusion

Hi all,
I am interested in bonding two Si wafers (coated with several microns of oxide, embedded with small features of silicon) with high alignment accuracy.  Does anyone have experience with this?  I assume the evbond would be suited for this, but the wiki only describes bonding between Si and glass.  I assume a post bond anneal would improve the bond b/w silicon features.  EVG website specs 2um (3sigma) alignment tolerances for backside alignment on the EVG620 aligner.  Is this level of precision important for others and has anybody actually observed the tool performing to these specs?
Thanks,
Chris