MOCVD of SrTa₂O₆Thin Films for High-k Applications

Abstract

SrTa2O6 thin films with thickness between 6 and 150nm were deposited in a multi-wafer planetary MOCVD reactor combined with a TRIJET® liquid delivery system using a single source precursor, strontium-tantalum-(methoxyethoxy)-ethoxide dissolved in toluene. A rather narrow process window for the deposition of stoichiometric SrTa2O6 was found for this precursor at low pressures and a susceptor temperature around 500°C. Films were grown on Pt/TiO2/SiO2/Si, TiNx/Si, and SiO2/Si substrates. The as-deposited films were X-ray amorphous and could be crystallized by post-annealing at a temperature ≥700°C. The SrTa2O6 phase was dominating within a broad range of compositions (Sr/Ta: 0.4–0.7) and a perovskite type phase was observed for Sr/Ta > 0.7. The electrical properties have been investigated with MIM and MIS capacitors after sputter deposition of Pt top electrodes. The amorphous films had a relative permittivity, ε, in the range of 25–45, and low leakage currents. Crystallized films were investigated with Pt MIM capacitors. For stoichiometric SrTa2O6 the dielectric permittivity reached values of ε = 100–110, but the leakage currents were increased. Remarkably, the permittivity is not very sensitive to deviations from the exact stoichiometry of the SrTa2O6 phase (Sr/Ta: 0.40.7), but a decrease to values of ε = 30–40 is observed along with the phase transition at high Sr contents.

SrTa 2 O 6 thin films for high-K dielectric applications grown by chemical vapor deposition on different substrates

“…3 Different phases of STA, which contain perovskitelike building blocks, are known for some time, but the processing of ceramics needs high temperatures and quite complicated processing strategies. 4 However, along with the development of chemical deposition methods for thin films of ferroelectric SrBi 2 Ta 2 O 9 , precursors became available, which allow for a straightforward deposition of STA thin films by chemical solution deposition ͑CSD͒, 4-6 metalorganic chemical vapor deposition ͑MOCVD͒, 7,8 and atomic layer deposition ͑ALD͒. 3,9,10 Films have been deposited on Pt/Si by CSD, 4 MOCVD, 8 and ALD ͑Ref.…”

“…4 However, along with the development of chemical deposition methods for thin films of ferroelectric SrBi 2 Ta 2 O 9 , precursors became available, which allow for a straightforward deposition of STA thin films by chemical solution deposition ͑CSD͒, 4-6 metalorganic chemical vapor deposition ͑MOCVD͒, 7,8 and atomic layer deposition ͑ALD͒. 3,9,10 Films have been deposited on Pt/Si by CSD, 4 MOCVD, 8 and ALD ͑Ref. 3͒ and on SiO x /Si͑100͒ by CSD, 5,6 MOCVD, 7,8 and ALD.…”

“…3,9,10 Films have been deposited on Pt/Si by CSD, 4 MOCVD, 8 and ALD ͑Ref. 3͒ and on SiO x /Si͑100͒ by CSD, 5,6 MOCVD, 7,8 and ALD. 9,10 Considering the dependence of the electrical properties of the films on stoichiometry and annealing temperature, the results obtained after deposition by the different chemical methods on Pt/Si seem very consistent.…”

“…9,10 Considering the dependence of the electrical properties of the films on stoichiometry and annealing temperature, the results obtained after deposition by the different chemical methods on Pt/Si seem very consistent. 3,4,8 For the films grown on Si the interfacial layer of SiO x is important and reduces the effective dielectric constant dependent on the film thickness, 5,9 this interfacial layer growth can be reduced by an oxygen diffusion barrier of oxinitride, SiON. 5,6 Nevertheless, an astonishing high capacity, as characterized by the equivalent oxide thickness ͑EOT͒ of a capacitor with a SiO 2 dielectric, of ϳ1 nm has been reported for 5-nm thick STA layers independent of the interlayer.…”