Uniform TiN-Capped Co Buried Bit Lines for 4F ² DRAM Vertical Channel Transistors: Mitigating Agglomeration with Co Nitridation

Recently, due to the high demand for high-density memory, the cell architecture of the vertical transistors has been continuously shrunk from 6F2 to a more compact 4F2. The bit lines (BLs) play an important role in fulfilling the functions of such scaled, vertically stacked arrays. Here, we report the formation of conformable Co-linear films covering the vertical structures with a high aspect ratio (AR), i.e., ∼8:1, using the chemical vapor deposition (CVD) technique. A detailed microscopic analysis was performed on the comfortable Co layers capped by TiN films by using a transmission electron microscope (TEM). The Co layers were damaged after the deposition of TiN layers, which resulted in the agglomeration of the Co layers. A nitridation process of Co layers was introduced to form a uniform and continuous Co layer. Our work paves a new way for forming well protected and highly uniform Co silicide-based buried BLs interconnecting the arrays of vertical transistors.