Advanced cyclopentadienyl precursors for atomic layer deposition of ZrO2 thin films

Abstract

ZrO₂ thin films were grown onto silicon (100) substrates by atomic layer deposition (ALD) using novel cyclopentadienyl-type precursors, namely (CpMe)₂ZrMe₂ and (CpMe)₂Zr(OMe)Me (Cp = cyclopentadienyl, C₅H₅) together with ozone as the oxygen source. Growth characteristics were studied in the temperature range of 250 to 500 °C. An ALD-type self-limiting growth mode was verified for both processes at 350 °C where highly conformal films were deposited onto high aspect ratio trenches. Signs of thermal decomposition were not observed at or below 400 °C, a temperature considerably exceeding the thermal decomposition temperature of the Zr-alkylamides. Processing parameters were optimised at 350 °C, where deposition rates of 0.55 and 0.65 Å cycle⁻¹ were obtained for (CpMe)₂ZrMe₂/O₃ and (CpMe)₂Zr(OMe)Me/O₃, respectively. The films grown from both precursors were stoichiometric and polycrystalline with an increasing contribution from the metastable cubic phase with decreasing film thickness. In the films grown from (CpMe)₂ZrMe₂, the breakdown field did not essentially depend on the film thickness, whereas in the films grown from (CpMe)₂Zr(OMe)Me the structural homogeneity and breakdown field increased with decreasing film thickness. The films exhibited good capacitive properties that were characteristic of insulating oxides and did not essentially depend on the precursor chemistry.