Approaches for patterning of aluminum

In semiconductor technology, aluminum is the preferred metallization. Sophisticated structures use a sandwich layer consisting of a Ti/TiN or TiW barrier layer, the aluminum itself, and Ti/(TiN) on top (ARC, electromigration enhancement, adhesion layer). For the patterning of these sandwiches, dry etching (RIE - Reactive Ion Etching) methods based on chlorine and bromine chemistries an commonly used. Etching tools are standard parallel-plate reactors, Hexode-systems, MERIE-systems, and, recently, inductive-coupled plasma sources. In this paper the different chemistries including the new aluminum/iodine system are discussed, as well as the different etching equipment. New approaches try to substitute RIE by chemical mechanical polishing (CMP), also called 'Damascene'. In this process sequence, the isolation oxide is deposited first, and the aluminum structure is etched into the oxide by RIE methods using a photoresist mask. After oxide etching and resist removal, the aluminum is filled in the structures and the residual aluminum is polished away by CMP. Finally, a second isolation layer is deposited. This paper will analyze this new approach and will compare it to the existing RIE methods.