Surface Morphologies and Electrical Properties of (Ba, Sr)TiO₃ Films Prepared by Two-Step Deposition of Liquid Source Chemical Vapor Deposition

Abstract

Protrusions of (Ba, Sr)TiO3 (BST) crystallites were found to appear on BST film surfaces prepared by liquid source chemical vapor deposition (CVD) at a substrate temperature T s=420° C and a reactor pressure P=1.5 Torr. Such protrusions were successfully suppressed by two-step deposition, where BST films consisted of a buffer layer and a main layer; the buffer layer was a CVD-BST film about 60 Å thick annealed in N2 ambient. By this two-step deposition on Pt electrodes, the BST film properties of equivalent SiO2 thickness t eq=0.56 nm, leakage current J L=1.2×10-8 A/cm2 at +1.1 V and dielectric loss tan δ=0.011 were achieved at a total film thickness of 230 Å, along with a coverage of 80% at a trench of aspect ratio 0.65 and sufficiently low absorption current.

Electrical properties of (Ba,Sr)TiO3 thin films revisited: The case of chemical vapor deposited films on Pt electrodes

“…There is generally quite good agreement with published values of the dielectric constant ͑DK͒ of as-deposited films, 3,11,12,25,[30][31][32][33] however, a detailed comparison is reasonable only for larger thickness series. In addition, the limited range of the linear 1 / C behavior, which has been observed by different groups, corroborates this comparison; a flatting of the slope of the 1 / C curve is observed at larger thickness 11,33 as well as an increase of the slope.…”

(Ba,Sr)TiO3 Thin Films for Dram’s

“…Even further improvements were achieved by using a four step process of deposition of an ultrathin seed layer (6 nm), N2 rapid thermal anneal, deposition of the rest of the BST, followed by a final N2 thermal anneal [56]. The properties obtained these different approaches are shown in Figure 22 [56]. The capacitance density is basically the same but the reported l~age current densities are lower for two deposition steps compared to just one.…”

“…This process achieved following the properties teq = 0.51 nm, J(1.1V) = 6.6 10-8 A/cm 2 , tan(8) = 0.007, and step coverage = 0.8 [54]. Even further improvements were achieved by using a four step process of deposition of an ultrathin seed layer (6 nm), N2 rapid thermal anneal, deposition of the rest of the BST, followed by a final N2 thermal anneal [56]. The properties obtained these different approaches are shown in Figure 22 [56].…”

“…A) Equivalent oxide thickness versus BST film thickness. B) Leakage current density at 1.6 V versus film thickness (redrawn from [56]). …”

Internal Microstructure and Formation Mechanism of Surface Protrusions in Pb-Ti-Nb-O Thin Films Prepared by MOCVD

“…For example, Kawahara et al observed many surface protrusions in dielectric bismuth strontium titanate (BST) films prepared by CVD. [10] The origin of these surface defects was ascribed to insufficient crystallization during the film deposition, and a two-step deposition process was proposed to hinder defect formation. Kim and Lee reported on significantly improved dielectric constant and leakage current density in a hillock-free BST film.…”