O-3-based atomic layer deposition of hexagonal La2O3 films on Si(100) and Ge(100) substrates

The hexagonal phase of La2O3 is obtained upon vacuum annealing of hydroxilated La2O3 films grown with atomic layer deposition at 200 degrees C using La((PrCp)-Pr-i)(3) and O-3. A dielectric constant value of 24 +/- 2 and 22 +/- 1 is obtained on Si-based and Ge-based metal-oxide-semiconductor capacitors, respectively. However, the relatively good La2O3 dielectric properties are associated with significant interface reactivity on both semiconductor substrates. This leads to the identification of a minimum critical thickness that limits the scaling down of the equivalent oxide thickness of the stack. These findings are explained by the spontaneous formation of lanthanum silicate and germanate species which takes place during the growth and also upon annealing. Although the ultimate film thickness scalability remains an unsolved concern, the use of an O-3-based process is demonstrated to be a suitable solution to fabricate La2O3 films that can be successfully converted into the high-k hexagonal phase.