Compatibility of silicon gates with hafnium-based gate dielectrics

D. C. GilmerCorresponding Author Contact Information, E-mail The Corresponding Author, R. Hegde, R. Cotton, J. Smith, L. Dip, R. Garcia, V. Dhandapani, D. Triyoso, D. Roan, A. Franke, R. Rai, L. Prabhu, C. Hobbs, J. M. Grant, L. La, S. Samavedam, B. Taylor, H. Tseng and P. Tobin

Digital DNA Laboratories, Advanced Products Research and Development Laboratory, Motorola, 3501 Ed Bluestein Boulevard, Austin, TX 78721, USA

Available online 11 June 2003.


Silicon gate compatibility problems with hafnium-based gate dielectrics are reported. It generally can be stated that chemical vapor deposition (CVD) silicon gates using silane deposited directly onto polycrystalline HfO2 at conventional temperatures (near 620 °C) results in (1) a low density of large inhomogeneous polycrystalline-silicon (poly-Si) grains, (2) electrical properties much worse compared to similar HfO2 films using metal gates or silicon gates with low temperature deposition. However, depositing conventional CVD poly-Si gates directly onto Al2O3-capped, hafnium–silicate-capped, or physical vapor deposition (PVD) silicon-capped HfO2 resulted in the absence of large inhomogeneous poly-Si grains and well behaved capacitors with leakage reduction greater than 103 times compared to the poly-Si/HfO2 and poly-Si/SiO2 controls of similar electrical thickness. The two observed adverse phenomena for conventional poly-Si deposited directly on HfO2 are attributed to a partial reduction of the HfO2 by the poly-Si deposition ambient. In the first case (1) the partial reduction occurs locally on the HfO2 surface, forming Hf–Six bond(s) which act as nucleation points for crystalline silicon growth while in the second case (2) the partial reduction occurs along grain boundaries resulting in electrical traps that increase film leakage. In addition, it is postulated that similar adverse interactions with conventionally deposited CVD poly-Si may occur with any transition metal oxide whose metal can form stable silicides.

Author Keywords: HfO2; Al2O3; Hafnium silicate; Hafnium aluminate; Dielectric

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