Method for making metal plugs in stacked vias for multilevel interconnections and contact openings while retaining the alignment marks without requiring extra masking steps

摘要

A method for making stacked metal plugs in via holes and contacts was achieved, while retaining alignment marks without using additional masking steps. The method involves the deposition of a barrier layer and a tungsten layer, which fill the via holes or contact openings in an insulating layer. The tungsten is then etched back, without overetching, to the surface of the barrier layer to form tungsten plugs that are coplanar with the surface of the insulating layer. Concurrently the tungsten is removed from the recessed alignment marks, which allows for the replication of the alignment marks in the next level of metal, thereby eliminating additional masking steps. The residual tungsten left on the surface after etch-back is removed by a short chemical/mechanical polishing to eliminate defects. The etch-back also removes the tungsten from the beveled edge of the substrate that can cause peeling and additional defects. The method can be repeated several times to form additional levels of interconnecting metal having stacked vias.