migration between the cap 120 and the bulk copper layer 110 the barrier layer 170 enhances the electomigration lifetime reduces migration of the conductor 110 which also reduces so called stress migration in comparing the two different cap layers 120 formed in fig7 and in fig1 while in fig1 the cap layer 120 may be reduced in thickness because of the provision of barrier layer 170 the cap layer 120 cannot be eliminated entirely or reduced in thickness beyond a given amount e g 300 angstroms because of lithographic misalignments that can arise in the formation of the via 148 for instance instead of forming via 148 in the ideal manner shown in fig8 misalignments may give rise to the micro trench 188 shown in fig1 and 14 when ild 130 is etched if the cap layer 120 is either too thin or not present at all that is a micro trench 188 may be formed adjacent the copper layer 105 if the cap layer 120 is too thin to serve as an etch stop because once the cap layer 120 is etched through the ild 105 is etched at a high etching rate because there is no etching selectivity between ild 130 and ild 105 that is if the cap layer 120 is too thin or not present the etching step used to form the via 148 may inadvertently continue through the ild 105 thereby creating the micro trench 188 because the degree of misalignment is likely to be small the micro trench 188 will generally be relatively narrow in the lateral direction because of its narrowness the micro trench 188 can be difficult to fill or otherwise eliminate accordingly despite the use of a barrier layer 170 in the conventional process the cap layer.