Difference Between Atomic Layer Deposition TiAl and Physical Vapor Deposition TiAl in Threshold Voltage Tuning for Metal Gated NMOSFETs

In this work, the influence of TiAl gate electrode fabricated by atomic layer deposition (ALD) and physical vapor deposition (PVD) on threshold voltage ( $\text{V}_{\text {t}}$ ) for metal-gated NMOSFETs is respectively investigated. Compared to ALD TiAl, the 200 mV lower $\text{V}_{\text {t}}$ for PVD TiAl is demonstrated and attributed to the oxidation of TiAl with a strong segregation of Ti near TiAl/TaN interface. It is further revealed that by changing the thickness of the first layer ALD TiAl film, the multi- $\text{V}_{\text {t}}$ can be easily obtained within a range of 200 mV using an ALD TiAl /PVD TiAl double layer gate electrode.