Pulsed chemical vapor deposition of conformal GeSe for application as an OTS selector. Issue 5 (3rd February 2021)

• Record Type: Journal Article
• Authors: Haider, Ali; Deng, Shaoren; Devulder, Wouter; Maes, Jan Willem; Girard, Jean-Marc; Khalil El Hajjam, Gabriel; Kar, Gouri Sankar; Opsomer, Karl; Detavernier, Christophe; Givens, Michael; Goux, Ludovic; Van Elshocht, Sven; Delhougne, Romain; Delabie, Annelies; Caymax, Matty; Swerts, Johan
• Is Part Of: Materials advances. Volume 2:Issue 5(2021)
• Page Start: 1635
• Page End: 1643
• Publication Date: 2021-02-03
• Subjects: 620.11
• DOI: 10.1039/d0ma01014f
• Languages: English
• ISSNs: 2633-5409

Abstract

Abstract : Pulsed CVD can be utilized to deposit GeSe in a highly conformal fashion. Abstract : The ovonic threshold switch (OTS) selector based on the voltage snapback of amorphous chalcogenides has received tremendous attention as it provides several desirable characteristics such as bidirectional switching, a controllable threshold voltage, high drive currents, and low leakage currents. GeSe is a well-known OTS selector that fulfills all the requirements imposed by future high-density storage class memories. Here, we report on pulsed chemical vapor deposition (CVD) of amorphous GeSe by using GeCl2 ·C4 H8 O2 as a Ge source and two different Se sources namely bis-trimethylsilylselenide ((CH3 )3 Si)2 Se (TMS)2 Se and bis-triethylsilylselenide ((C2 H5 )3 Si)2 Se (TES)2 Se. We utilized total reflection X-ray fluorescence (TXRF) to study the kinetics of precursor adsorption on the Si substrate. GeCl2 ·C4 H8 O2 precursor adsorption on a 300 mm Si substrate showed under-dosing due to limited precursor supply. On the other hand, the Se precursor adsorption is limited by low reaction efficiency as we learned from a better within-wafer uniformity. Se precursors need Cl sites (from Ge precursor) for precursor ligand exchange reactions. Adsorption of (TMS)2 Se is found to be much faster than (TES)2 Se on a precoated GeCl x layer. Atomic layer deposition (ALD) tests with GeCl2 ·C4 H8 O2 and (TMS)2 Se revealed that the growth per cycle (GPC) decreases with the introduction of purge steps in the ALD cycle, whereas a higher GPC is obtained in pulsed-CVD mode without purges. Based on this basic understanding of the process, we developed a pulsed CVD growth recipe (GPC = 0.3 Å per cycle) of GeSe using GeCl2 ·C4 H8 O2 and (TMS)2 Se at a reactor temperature of 70 °C. The 20 nm GeSe layer is amorphous and stoichiometric with traces of chlorine and carbon impurities. The film has a roughness of ∼0.3 nm and it starts to crystallize at a temperature of ∼370 °C. GeSe grown on 3D test structures showed excellent film conformality.