Influence of Substrates on the Nucleation and Growth Behaviors of Ge2Sb2Te5 Films by Combined Plasma-Enhanced Atomic Layer and Chemical Vapor Deposition

This study concerned the effect of the substrate on the nucleation and growth behavior of Ge2Sb2Te5 (GST) thin films deposited by a combination of plasma-enhanced chemical vapor deposition (for Sb and Te) and plasma-enhanced atomic layer deposition (for Ge) processes at wafer temperatures ranging from 100 to 200 °C using Ge(i-C4H9)4, Sb(i-C3H7)3, and Te(i-C3H7)2 as the Ge, Sb, and Te precursors, respectively. Several oxide and nitride layers that were formed on the Si substrate were concerned as substrates. The nucleation of the GST films on the SiO2, Si3N4, and ZrO2 substrates was seriously retarded (long incubation cycles) compared to those on the TiN and TiO2 substrates, where smooth film growth with negligible incubation cycles was achieved. The GST film did not grow at all on the HfO2 substrate. The reason for the enhanced nucleation and growth properties of GST on the TiO2 and TiN (partially oxidized) substrates was related to the formation of a GeO2 phase and the charge exchange effect of a partially reduced Ti oxide. On the other hand, the SiO2 surface remained insulating during deposition, which inhibited GST nucleation. The different nucleation behaviors also influenced the crystallization behavior of the film, which in turn altered the saturated film growth rates. It is believed that the crystallized GST surface reduced the activation energy for the chemisorption of the precursors, which enhanced the saturated growth rate.