Conformal Step Coverage of (Ba,Sr)TiO₃ Films Prepared by Liquid Source CVD Using Ti(t-BuO)₂(DPM)₂

Abstract

We study the application of (Ba,Sr)TiO 3 (BST) films prepared by chemical vapor deposition (CVD) method to ∼0.13-µm-scale devices, for example, 4Gbit dynamic random access memories (DRAMs), whose minimum feature size and height of storage nodes are around 0.13 and 0.36 µm, respectively. It is necessary for these devices to obtain a conformal step coverage of the BST films of more than 80% at an aspect ratio of 3–5, along with an equivalent SiO 2 thickness ( t eq ) of 0.5 nm. Recently, a new Ti source, Ti( t -BuO) 2 (DPM) 2 [bis ( t -butoxy) bis (dipivaloylmethanato) titanium], whose Ti ion is surrounded by four large organic ligands, was developed. It is more stable in THF (tetrahydrofuran; C 4 H 8 O) solution and in the vapor phase than conventional Ti sources such as TiO(DPM) 2 [oxo bis (dipivaloylmethanato) titanium]. In fact, the step coverages of the BST films using Ti( t -BuO) 2 (DPM) 2 were found to be 80% and 70% at aspect ratios of 3.3 and 5, respectively, which were much better than those of films using TiO(DPM) 2 . Moreover, the electrical properties of the BST films using Ti( t -BuO) 2 (DPM) 2 were t eq =0.44 nm and a leakage current J L of 2.8× 10 -8 A/cm 2 (+1.1 V) for a film of 24 nm thickness after post-annealing. These characteristics meet the requirements of the 4Gbit DRAM capacitors.