(A) study on $SrTiO_3$ thin films deposited by plasma-enhanced atomic layer deposition for DRAM capacitor dielectric

Abstract

The downscaling of the DRAM device is necessary to achieve higher speed with less power consumption. It is getting difficult to meet the new requirements with the existing $SiO_2$ or $Si_3N_4$ due to their low dielectric constants and tunneling leakage currents through the thin layers. For this reason, high-$\textit{k}$ materials enabling high-k and low leakage currents with physically thicker film have received considerable attention. Among the candidate for DRAM capacitor dielectrics, $SrTiO_3$ is a promising candidate for giga-bit scale dynamic random access memory (DRAM) capacitors because of its high dielectric constant, high breakdown strength and good thermal stability. $SrTiO_3$ films were deposited on 20 nm-Ru/25 nm-TiN/p-type Si (100) substrates by plasma-enhanced atomic layer deposition at a deposition temperature of 225℃ and a deposition pressure of 3 Torr using 0.2M $Sr(DPM)_2$ dissolved in butyl acetate and TTIP as precursors and $O_2$ plasma as an oxidant. SrO and $TiO_2$ films were grown separately to investigate the ALD characteristics. The thickness per cycle of SrO and $TiO_2$ are saturated to 0.054 nm/cycle 0.036 nm/cycle at 225℃, respectively. The composition of STO films was controlled by changing the number of each precursor cycles, and stoichiometric $SrTiO_3$ films were obtained when one super-cycle consisted of six $TiO_2$ cycles and seven SrO cycles. The deposited-$SrTiO_3$ films were crystallized after annealing at 600℃ for 10min under $N_2$ ambient and the dependence of the dielectric constant on $SrTiO_3$ film thickness was investigated for less 50 nm-thick $SrTiO_3$ films after the annealing process at 600℃ for 10 min under $N_2$ ambient. The dielectric constants of the films having thickness higher than 20 nm were not as sensitive to the film thickness with a relatively constant value of about 65. However, the dielectric constants of the films with thickness under 15 nm were dramatically decreased with decreasing the fil...