Texture and surface morphology improvement of Al by two-stage chemical vapor deposition and its integration in an Al plug-interconnect scheme for sub 0.25 μm metallization

Abstract

A two-stage deposition with successive seed and bulk deposition steps was developed to improve the morphology and texture of chemical vapor deposited (CVD) aluminum on titanium. Dimethylaluminumhydride (DMAH) was used as the precursor. Typically, CVD Al deposited using a single deposition stage showed highly granular structure with surface “defects” resulting in films that become rough with increase in thickness creating integration problems with photolithography and etch. Here, a two-stage deposition process for CVD Al is described that significantly improves the morphology and texture of Al on titanium. In this process, the wafer surface is preconditioned with a short burst of DMAH before stabilizing gas flows or pressure. Such a treatment in the very first step results in a seed layer upon which proceeds the bulk film deposition in a subsequent step after stabilizing pressure, gas flows and equilibrating temperature. The two-stage deposition resulted in reflectivity improvement of CVD Al on Ti from ⩽ 160% to >210% (%Si, 480 nm) for a 3.5 kÅ thick film with complete elimination of surface defects. X-ray rocking curves show a decrease in the full width at half maximum of the Al(111) peak from 5.1° to 2.6°, indicating significantly improved texture. Secondary ion mass spectroscopy analysis of the CVD Al shows a decrease in carbon content using the two-stage deposition. The two-stage deposition for CVD Al was integrated with AlCu sputter process at temperatures below 380 °C, without a vacuum break between the CVD Al and PVD AlCu, to develop sub-0.25 μm technology via fill capability.