Atomic Layer Deposition of Hexagonal-Phase Ta[sub 2]O[sub 5] Using TaF[sub 5] and H[sub 2]O

The results of atomic layer deposition of Ta 2 O 5 on silicon using the precursors Ta F 5 and H 2 O are reported. The films are stoichiometric Ta 2 O 5 at the surface, becoming Ta-rich as the interface is approached. For deposition temperatures from 400 to 450 ° C and chamber pressures from 0.5 to 5 Torr , the deposition rate exhibits two growth regimes, postulated to be due to differences in the densities of hydroxyl species on the chemically cleaned Si substrates and on the deposited Ta 2 O 5 layer. Growth rate in the “converged” regime, in which Ta 2 O 5 has completely covered the substrate, is more strongly affected by the partial pressure of the Ta F 5 than by that of the H 2 O . A comparison is made between the growth rate and the surface coverage of Ta F 5 calculated with a simple Langmuir model. The deposited phase changes from amorphous to crystalline (hexagonal) in the same interval of pressure and temperature. The controlling factor for formation of the hexagonal polymorph is the partial pressure of the Ta F 5 precursor. The extent of surface coverage of Ta F 5 alone does not adequately account for the dependence of the extent of crystallization on pressure and temperature, and it is likely that there are additional important surface reaction components.