Suppression of electronic defects induced by GeO _x at the high- k gate oxide/SiGe interface is critical for implementation of high-mobility SiGe channels in complementary metal-oxide-semiconductor (CMOS) technology. Theoretical and experimental studies have shown that a low defect density interface can be formed with an SiO _x-rich interlayer on SiGe. Experimental studies in the literature indicate a better interface formation with Al₂O₃ in contrast to HfO₂ on SiGe; however, the mechanism behind this is not well understood. In this study, the mechanism of forming a low defect density interface between Al₂O₃/SiGe is investigated using atomic layer deposited (ALD) Al₂O₃ insertion into or on top of ALD HfO₂ gate oxides. To elucidate the mechanism, correlations are made between the defect density determined by impedance measurements and the chemical and physical structures of the interface determined by high-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. The compositional analysis reveals an SiO _x rich interlayer for both Al₂O₃/SiGe and HfO₂/SiGe interfaces with the insertion of Al₂O₃ into or on top of the HfO₂ oxide. The data is consistent with the Al₂O₃ insertion inducing decomposition of the GeO _x from the interface to form an electrically passive, SiO _x rich interface on SiGe. This mechanism shows that nanolaminate gate oxide chemistry cannot be interpreted as resulting from a simple layer-by-layer ideal ALD process, because the precursor or its reaction products can diffuse through the oxide during growth and react at the semiconductor interface. This result shows that in scaled CMOS, remote oxide ALD (oxide ALD on top of the gate oxide) can be used to suppress electronic defects at gate oxide semiconductor interfaces by oxygen scavenging.

Joanna Cheung

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