Nucleation and growth study of atomic layer deposited HfO ₂ 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 + H2 O. 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 + H2 O shows a surface dependence. Rutherford backscattering shows that HfCl4 + H2 O 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 >9 g cm3, and bulk Hf-O bonding after 15 cycles [physical thickness (Tphys) =1.2±0.2 nm] even on H-terminated Si(100). Conversely, on H-terminated Si(100), HfCl4 + H2 O requires 50 cycles (Tphys ∼3 nm) for continuous films and bulk Hf-O bonding. TEMAHf+ O3 ALD was implemented in HfO2 TiN transistor gate stacks, over the range 1.2 nm≤ Tphys ≤3.3 nm. Electrical results are consistent with material analysis suggesting that at Tphys =1.2 nm HfO2 properties begin to deviate from thick film properties. At Tphys =1.2 nm, 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 1.2 nm. This improvement may be attributed to reduced charge trapping and Coulomb scattering in thinner films. Scaled HfO2 enables 1 nm equivalent oxide thickness and 82% of universal SiO2 mobility.