(A) study on the $TiO_2/Al_2O_3$ thin film for DRAM capacitor dielectric by plasma-enhanced atomic layer deposition

Abstract

The downscaling of the DRAM devices 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-k materials enabling high-k and low leakage currents with physically thicker film have received considerable attention. $Al_2O_3$ added $TiO_2$ film attracts particular attention as a promising alternative to $SiO_2$ or $Si_3N_4$ from high-k and low leakage current considerations. In this work, $TiO_2$ and $Al_2O_3$ nanolaminated films deposited by plasma enhanced atomic layer deposition (PEALD) using titanium isopropoxide $(TTIP, Ti[OC_3H_7)]_4)$ and tri-methyl-aluminum $(TMA, Al(CH_3)_3)$ as metal precursors, respectively, and $O_2$ plasma as an oxidant were studied. The film characteristics were analyzed by structural, electrical, and compositional points. As the first method for reducing leakage current by addition $Al_2O_3$ to $TiO_2$, $TiO_2-Al_2O_3$ mixed films are deposited. The mixing ratio of $TiO_2$ and $Al_2O_3$ is controlled by unit-cycle number of super-cycle. Dielectric constant and leakage current are increased with increasing $TiO_2$ content in film. However, the maximum dielectric constant of mixed film is only 35.3, even $TiO_2$ content is increased to 86%. And also leakage current values of lower than 27% $Al_2O_3$ composition in mixed film are measured $10^{-4} A/cm^2$ level. In other words, dielectric constant is too low owing to high $Al_2O_3$ content for reducing leakage current by $TiO_2-Al_2O_3$ mixing method. This result presented that mixing method is not proper to reducing leakage current. So, lamination film, on which adding $Al_2O_3$ as a layer, is examined. As the second method for reducing leakage current, deposit $TiO_2/Al_2O_3$ laminated film adding $Al_2O_3$ as a nano-scale-thick layer. At first, finding maximu...