Planar Deposition of Aluminum by RF/DC Sputtering with RF Bias

Abstract

Planarization of multilevel interconnection is most effective for achieving a higher packing density. However, it is shown by computer simulation that degradation of metallization step coverage becomes serious as the via aspect ratio increases. Conventional deposition methods, in which emitted particles flow onto the substrate and usually do not migrate, are shown to be inadequate for maintaining sufficient step coverage. A new deposition technique, RF/dc sputtering with RF bias for metal, is developed and found to provide sufficient step coverage and, moreover, planarity. In an application of the technique to aluminum film deposition, the existence of a resputtering effect was confirmed. Aluminum particles were found to deposit primarily near the bottom of the depressions and to fill up the depressions completely, through sputtering at a high bias. Steep, deep grooves and vias with aspect ratios up to 3 were found to be completely filled with the aluminum film by deposition at resputtering rates higher than 50%. It was also found that substrate biasing has a decisive effect on giving aluminum films an almost complete (111) crystallographic texture.