Method for preventing Al-Cu bottom damage using TiN liner

A semiconductor device, comprising:

• a plurality of conductive columns extending from an insulating base layer and each comprising a respective lower barrier layer on the insulating base layer, a respective conductive layer on the respective lower barrier layer, and a respective overlying upper barrier layer on the respective conductive layer, wherein the conductive columns are electrically insulated from each other;
• wherein the conductive layer in each of the conductive columns is tapered creating an undercut region at an interface between the conductive layer of each conductive column and the respective overlying upper barrier layer;
• and
• a plurality of conductive liner layers, each respective over portions of a sidewall of the conductive columns, wherein each liner layer includes a first thickness portion over the undercut region, and a second thickness portion substantially adjacent to an interface between the lower barrier layer and the conductive layer;
• wherein the first thickness portion is greater than the second thickness portion.