Highly conformal ZrO2 deposition for dynamic random access memory application

Abstract

ZrO 2 is investigated in this work to replace SiO 2 as the dielectric material in metal–oxide–metal capacitors in dynamic random access memory (DRAM) devices for its high dielectric constant, good thermal stability, excellent conformality, and large band gap. ZrO 2 films were deposited on planar Si (100) wafers and patterned amorphous silicon cylinders by rapid thermal chemical vapor deposition process using a zirconium (IV) t-butoxide Zr(OC 4 H 9 ) 4 precursor and oxygen. At substrate temperature below 300 °C, no significant deposition was observed. At temperatures between 300 and 400 °C, the reaction is thermally activated with an activation energy of 29 kcal/mol, consistent with a β-hydride elimination mechanism leading to ZrO 2 deposition. In this regime, one atomic layer of ZrO 2 can be deposited after each alternating exposure to the precursor and oxygen, ideal for achieving conformal coverage of ZrO 2 over high aspect ratio features. At temperatures above 400 °C, the deposition rate is less sensitive to temperature with an apparent activation energy of 4 kcal/mol due to decomposition and desorption of the precursors. Stoichiometric, uniform, and amorphous ZrO 2 was obtained at all temperatures investigated. Highly conformal step coverage of the deposited ZrO 2 was achieved on 300 nm×600 nm cylindrical features with an aspect ratio of 4. The dielectric constant of ZrO 2 achieved in this work ranges from 15 to 18 depending upon process conditions and small capacitance–voltage hysteresis is observed, ideal for DRAM application.