(A) study on the plasma-enhanced atomic layer deposition of $SrTiO_3$ thin films

Abstract

$SrTiO_{3}$ 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 have been deposited by plasma-enhanced atomic layer deposition (PEALD) at 200~300℃ from $Sr(DPM)_{2}$ and TTIP (titanium tetra-isopropoxide) as precursors with $O_{2}$ plasma. To control the film composition, after one precursor was injected and converted to films completely, the other was injected into the reactor. Therefore we define sub-cycle as follows: precursor pulse, $Ar/O_{2}$ purge pulse, $Ar/O_{2}$ plasma and $Ar/O_{2}$ purge pulse. And super-cycle is consisted of sum of each precursor sub-cycles. 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 0.48Å/cycle 0.35Å/cycle at 275℃, respectively. This saturation behavior results from the number of available adsorption sites. Therefore, the growth of SrO and $TiO_{2}$ films at 275℃ followed the self-controlled growth mechanism typical of PEALD. STO films were deposited based on the obtained results. When super-cycle consisted of sum of one Ti sub-cycle and one Sr sub-cycle, thickness per super-cycle was 0.61Å /super-cycle and STO films with Ti contents of 0.55 were deposited. It shows that adsorption probability of precursor onto heterogeneous film surface is low and adsorption probability of TTIP onto SrO-terminated surface is higher than that of $Sr(DPM)_{2}$ onto $TiO_{2}$-terminated surface. Also, it is possible to increase or decrease the composition of wanted element by changing the number of each precursor sub-cycles. Stoichiometric $SrTiO_{3}$ films were obtained when super-cycle consisted of 11 times Ti sub-cycle and 10 times Sr sub-cycle. As a result, Ti rich film that the composition ratio of Ti to Sr is 0.51 to 0.49 was obtained from AES analysis. The crystal structure of as-depos...