Atomic layer deposition of transition metals for silicide contact formation: Growth characteristics and silicidation

The atomic layer deposition (ALD) is a promising thin film deposition technique in the fabrication of nanoscale semiconductors devices. In this paper, the results on the ALD of transition metals are reviewed for their applications as silicide contact of nanoscale semiconductor devices, especially focusing on the growth characteristics of ALD Co (and Ni) and comparison between plasma-enhanced ALD (PE-ALD) and thermal ALD (TH-ALD). For most of metal organic precursors, NH₃ plasma is a good choice as a reactant to produce highly pure Co or Ni films, while H₂ or N₂ plasma does not produce high quality film. At optimal conditions, highly pure Co films were deposited with low resistivity down to 10 μΩ cm. Relatively good quality metal film formation by thermal ALD was possible by limited range of precursors including Co(iPr-AMD)₂. Even for these precursors, the resistivity and other film properties were inferior to those of PE-ALD films. However, for PE-ALD using NH₃ plasma, the conformality was not good enough for high aspect ratio nanoscale via structures, which necessitates the development of thermal ALD process. The formation of silicide by rapid thermal annealing of ALD Co thin films was also investigated showing different behavior for PE- and TH-ALD Co thin films.