| AVS 62nd International Symposium & Exhibition | |
| Selective Deposition as an Enabler of Self-Alignment Focus Topic | Thursday Sessions |
| Session SD+AS+EM+PS-ThA |
| Session: | Process Development for Selective Deposition and Self-aligned Patterning |
| Presenter: | ByungJoon Choi, Seoul National University of Science and Technology, Republic of Korea |
| Authors: | B.J. Choi, Seoul National University of Science and Technology, Republic of Korea T. Eom, Seoul National University, Republic of Korea C.S. Hwang, Seoul National University, Republic of Korea |
| Correspondent: | Click to Email |
GST Phase changing material, typically GeTe–Sb2Te3 pseudo-binary solid solution, has been extensively studied for rewritable digital versatile optical disks or phase change random access memory (PcRAM), on account of the drastic change of its optical reflectivity or electrical resistivity between amorphous and crystalline phases. As the device size of PcRAM is scaled down, GST materials should be confined into the contact-plug for reducing its programming current, which cannot be achieved by any physical deposition method.
Among the various metal-organic (MO) precursors, the combination of Ge(iBu)4, Sb(iPr)3 and Te(iPr)2 has been extensively studied for plasma enhanced chemical vapor depostion or its variant methods with plasma-activated H2 gas as a reducing agent of the MO-precursors. Plasma-enhanced pulsed CVD was attempted using the precursor pulse sequence consisting of Sb–Te–Ge–Te cycles (each elemental cycle is composed of precursor injection and Ar + H2 plasma reduction steps). The chemical composition of the films was appropriately controlled by the cycle ratio and sequence of each precursor pulse. The linear growth with the number of cycles was shown, and the GPC (growth-per-cycle, i. e. growth rate) was determined to be 0.73 nm/super-cycle from the slope at a wafer temperature of 200◦C.
Strong substrate dependency can be utilized in the selective growth of GST material on a TiN contact-plug formed in the SiO2 inter-layer dielectric (ILD). Higher selectivity (difference of GPC) between TiN contact-plug and SiO2 ILD layer was achieved by pulsed CVD with increasing the amount of Te(iPr)2 injection. The reason for the selective growth was believed to have originated from the adverse interference of the residual gas (unreacted Te(iPr)2 or its derivatives) to the chemical adsorption of Sb nuclei on the SiO2 surface, which functions as a nucleation site for further GST growth. It was reported that amide-based Ge precursors also showed strong selectivity at a particular temperature, enabling Sb and Te precursors to be chemisorbed on the Ge seed layer, which could be utilized for selective growth of GST.
The most feasible explanation for the substrate-dependent growth behavior of the GST film is the electron donation from the substrate, which would enhance the precursor decomposition and removal of ligands from the adsorbed precursor molecules. The nucleation and growth behaviors of the GST films were studied on Si substrates with various nucleation or buffer layers. It turned out that the types of substrates have a crucial impact on the nucleation behaviors and the chemical composition of the film.