Paper TF2-TuM5
Growth of GeTe Films by MOCVD and PE-MOCVD for Phase Change Memory

Tuesday, October 19, 2010, 9:20 am, Room Ruidoso

Phase-Change Memory (PCM) is one of the promising candidates for next-generation nonvolatile memory thanks to their low cost, low programming voltage and their excellent scalability to the nanoscale cell size [1]. This technology is based on fast and reversible phase change effect in the chalcogenide materials but suffers of the inherent lack of amorphous state stability which affects archival life of the memory cell. This proble is critical for embedded applications where a high retention time at high working temperature is required. In this case, binary compound GeTe material has been shown to be a good candidate since a phase transition temperature higher than the usual Ge₂Sb₂Te₅ material has been found and 10 years-fail time at 105°C has been estimated [2]. Moreover the reduction of the current pulse needed to change material from crystal phase to amorphous phase implies the confinement of phase change materials at dimensions below 100 nm [3]. In this case the growth of GeTe materials by chemical vapour deposition (CVD) or Plasma Enhanced CVD is required in order to fill confined structures.

For this purpose, this work investigates the deposition of GeTe materials by a pulsed liquid injection Metal Organic CVD system allowing storing the precursor at ambient temperature. The deposition is made in a 200 mm MOCVD tool that can be assisted by a Low Frequency as well as Radio Frequency plasma. The liquid precursors are injected into a heated evaporator where flash evaporation occurs. A sequential injection leads to a precise control of the deposited material stoichiometry. Furthermore deposition in amorphous or crystalline state is performed by setting the substrate temperature. This chamber is connected to a cluster tool which allows quasi in situ analysis of the deposited films crystalline state by Spectroscopic Ellipsometry (SE) and of the growth mechanisms by angle-resolved X-ray Photoelectron Spectroscopy (ARXPS). Impact of process parameters on the films properties are then evaluated in the MOCVD and PECVD mode. In the case of plasma assistance the impact of the Low to Radio Frequency ratio on the thin film deposition is also studied. Direct informations on Ge/Te ratio and carbon contamination are given by the plasma analysis thanks to optical emission spectrometry. In addition to the chemical and physical properties investigations, the phase change performances and the electrical properties of the deposited materials are evaluated.

[1] S. J. Hudgens, J. Non-Crys. Solids, 354, 2748 (2008)

[2] L. Perniola et al., IEEE Electron Device Lett., 31, 5 (2010), pp. 488-490.

[3] S. L. Cho et al., Symp. VLSI Tech. Dig. (2005), p. 96