A systematic investigation of work function in advanced metal gate-HfO2-SiO2 structures with bevel oxide

This paper presents for the first time the work function extraction for chemical vapor deposition (CVD)-TiN and poly-Si work functions on atomic layer deposition (ALD)-HfO 2 and high temperature SiO 2 (HTO) for a wide range of EOT values. The measurements were performed on bevel oxide structures with various SiO 2 thicknesses from 0 to 12 nm. Our results reveal that the work functions of both TiN and poly-Si gates highly depend on the underlying dielectrics especially in the case of TiN on HTO films. It is found that the leakage current also depends on the dielectric stacks. When TiN is formed on the HTO film, its work function has two distinct values depending on the HTO thickness; this indicates that Ti-Si bonds strongly affect the work function variation. Both TiN on HTO and poly-Si on HfO 2 show the work function shifts to about 4.3 eV, suggesting a pinning level in both structures.