Nucleation and growth study of atomic layer deposited $HfO2$ gate dielectrics resulting in improved scaling and electron mobility

$HfO2$ films have been grown with two atomic layer deposition (ALD) chemistries: (a) tetrakis(ethylmethylamino)hafnium $(TEMAHf)+O3$ and (b) $HfCl4+H2O$⁠. The resulting films were studied as a function of ALD cycle number on $Si(100)$ surfaces prepared with chemical oxide, HF last, and $NH3$ annealing. $TEMAHf+O3$ growth is independent of surface preparation, while $HfCl4+H2O$ shows a surface dependence. Rutherford backscattering shows that $HfCl4+H2O$ coverage per cycle is l3% of a monolayer on chemical oxide while $TEMAHf+O3$ coverage per cycle is 23% of a monolayer independent of surface. Low energy ion scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy were used to understand film continuity, density, and chemical bonding. $TEMAHf+O3$ ALD shows continuous films, density $>9g∕cm3$⁠, and bulk $Hf–O$ bonding after 15 cycles [physical thickness $(Tphys)=1.2±0.2nm$] even on H-terminated $Si(100)$⁠. Conversely, on H-terminated $Si(100)$⁠, $HfCl4+H2O$ requires 50 cycles $(Tphys∼3nm)$ for continuous films and bulk $Hf–O$ bonding. $TEMAHf+O3$ ALD was implemented in $HfO2∕TiN$ transistor gate stacks, over the range $1.2nm⩽Tphys⩽3.3nm$⁠. Electrical results are consistent with material analysis suggesting that at $Tphys=1.2nm$ $HfO2$ properties begin to deviate from thick film properties. At $Tphys=1.2nm$⁠, electrical thickness scaling slows, gate current density begins to deviate from scaling trendlines, and no hard dielectric breakdown occurs. Most importantly, $n$-channel transistors show improvement in peak and high field electron mobility as $Tphys$ scales from 3.3 to $1.2nm$⁠. This improvement may be attributed to reduced charge trapping and Coulomb scattering in thinner films. Scaled $HfO2$ enables $1nm$ equivalent oxide thickness and 82% of universal $SiO2$ mobility.