T. Kawahara et al., Conformal step coverage of (Ba,Sr)TiO3 films prepared by liquid source CVDusing Ti(t-BuO)(2)(DPM)(2), JPN J A P 1, 38(4B), 1999, pp. 2205-2209
We study the application of(Ba,Sr)TiO3 (BST) films prepared by chemical vap
or deposition (CVD) method to similar to 0.13-mu m-scale devices, for examp
le, 4Gbit dynamic random access memories (DRAMs), whose minimum feature siz
e and height of storage nodes are around 0.13 and 0.36 mu m, respectively.
It is necessary for these devices to obtain a conformal step coverage of th
e BST films of more than 80% at an aspect ratio of 3-5, along with an equiv
alent SiO2 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 (tetrahydrofuranl C4H8O) 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, respec
tively, which were much better than those of films using TiO(DPM)(2). Moreo
ver, the electrical properties of the BST films using Ti(t-BuO)(2)(DPM)(2)
were r(eq) = 0.44 nm and a leakage current J(L) Of 2.8 x 10(-8) A/cm(2) (+1
.1 V) for a film of 24 nm thickness after post-annealing. These characteris
tics meet the requirements of the 4Gbit DRAM capacitors.