Low Temperature Chemical Vapor Deposition of (Ba, Sr)TiO3 Thin Films for High Density Dynamic Random Access Memory Capacitors

Abstract

(Ba, Sr)TiO3 (BST) films are deposited on 8-inch wafers by the metal organic chemical vapor deposition (MOCVD) technique at a temperature as low as 400°C to obtain conformal step coverage and prevent oxidation of the diffusion barrier of simple stacked capacitors. The problems of low temperature process (formation of protrusions, titanium deficiency, severe thickness deviation) could be successfully overcome by proper modification of the CVD system and process conditions. Retrofitting the vaporizer to obtain flash evaporation of the liquid chemical source and introducing N2O gas as an oxidant were highly effective for reducing the thickness deviation and titanium deficiency. The Pt/BST/Pt capacitor with BST films deposited at 400°C and post-annealed at 700°C for 30 min under nitrogen ambient shows excellent electrical properties (Tox∼6.6 Å, J∼1×10-7 A/cm2 @±1 V), which are satisfactory for application to high density dynamic random access memory (DRAM) capacitors beyond 256 Mbit generation.