Evaluation of aluminum film properties and microstructure for replacement metal gate application at 28nm technology node

The fundamental film properties and microstructures of the different aluminum (Al) metal layers are evaluated to fabricate a replacement metal gate (RMG) device for the high-k metal gate (HKMG) application at 28 nm node. A PVD Al fill-in metal deposition process, called one step hot Al (HAL), was found the resistivity increases with increasing the thickness of the Ti wetting layer. The higher pinhole density with the preferred (111) crystal orientation in the HAL layers indicate the film properties with lower reflectivity, higher resistivity and lower removal rate of the Al chemical mechanical polishing (AlCMP). In contrast, the other PVD Al deposition approach, called two steps cold hot Al (CHAL), was identified to possess lower resistivity and higher reflectivity without pinhole structures than the HAL. The smaller grain sizes with the preferred (220) orientation in the CHAL could effectively prevent the formation of pinhole and enhance the removal rate of the AlCMP. The non-uniform with crystallized TiAl3 phase detected in the bottom of the as-deposited HAL and CHAL films could obviously impact the removal rate of the AlCMP. An optimized CHAL fill-in metal deposition process with a larger than 40 Å Ti wetting layer are needed to simultaneously meet the process requirements of the Al gapfill and AlCMP planarization for achieving a reliable RMG structures.