Nucleation and growth study of atomic layer deposited HfO2 gate dielectrics resulting in improved scaling and electron mobility -: art. no. 023508

HfO2 films have been grown with two atomic layer deposition (ALD) chemistries: (a) tetrakis(ethylmethylamino)hafnium (TEMAHf)+O-3 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+O-3 growth is independent of surface preparation, while HfCl4+H2O shows a surface dependence. Rutherford backscattering shows that HfCl4+H2O coverage per cycle is 13% of a monolayer on chemical oxide while TEMAHf+O-3 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+O-3 ALD shows continuous films, density > 9 g/cm(3), and bulk Hf-O bonding after 15 cycles [physical thickness (T-phys)=1.2 +/- 0.2 nm] even on H-terminated Si(100). Conversely, on H-terminated Si(100), HfCl4+H2O requires 50 cycles (T(phys)similar to 3 nm) for continuous films and bulk Hf-O bonding. TEMAHf+O-3 ALD was implemented in HfO2/TiN transistor gate stacks, over the range 1.2 nm <= T-phys<= 3.3 nm. Electrical results are consistent with material analysis suggesting that at T-phys=1.2 nm HfO2 properties begin to deviate from thick film properties. At T-phys=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 T-phys 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. (c) 2006 American Institute of Physics.