Effects of La₂O₃ capping layers prepared by different ALD lanthanum precursors on flatband voltage tuning and EOT scaling in TiN/HfO₂/SiO₂/Si MOS Structures

The use of thin capping layers that are inserted between the gate metal and dielectric layers have been shown to simultaneously cause a negative flatband voltage (V_fb) shift and to stabilize low threshold voltage (V _TH). A major challenge with capping layers is to achieve adequate effective work function shifts without large increases in equivalent oxide thickness (EOT) (EOT). In this work, the effects of La₂O₃ cap layers prepared by different ALD Lanthanum precursors, La(fAMD)₃ and La(thd)₃, on flatband voltage tuning and EOT scaling in TiN/HfO₂/"SiO"₂/Si metal oxide semiconductor (MOS) structures was investigated. Experimental results showed that V _fb and EOT as high as 0.45 V and 0.055 nm, caused by dipoles at the lower interface between HfO₂ and "SiO"₂ interlayer and the diffusion of La and Hf atoms to the "SiO" ₂ interlayer, were achieved by a 1 nm thick La₂O ₃ capping layer using a La(fAMD)₃ precursor, while a relatively smaller V_fb and EOT of -0.7 V and 1.27 nm were obtained from the noncap TiN/HfO₂/"SiO"₂/Si MOSCAP sample. The use of a La(fAMD)₃ precursor for the La₂O ₃ capping layer deposition has been shown being much superior to La(thd)₃ due to lower atomic layer deposition (ALD) process temperature and shorter O₃ oxidant pulse duration.