Deposition of extremely thin (Ba,Sr)TiO3 thin films for ultra-large-scale integrated dynamic random access memory application

Abstract

(Ba,Sr)TiO3 (BST) thin films with thicknesses ranging from 15 to 50 nm are prepared by a rf magnetron sputtering on Pt/SiO2/Si substrates. The dielectric constants of BST thin films increase with increasing deposition temperature and thicknesses. The leakage current increases with increasing deposition temperature and this prevents the deposition temperature of the 20 nm thick BST thin film from being increased to a value more than 640 °C. The leakage current is also critically dependent upon the postannealing temperature and atmosphere after the top electrode fabrication. The dielectric constant increases with increasing postannealing temperature which further reduces the SiO2 equivalent thicknesses of the BST thin films. A 20 nm thick BST thin film deposited at 640 °C and postannealed at 750 °C under N2 atmosphere for 30 min, shows a SiO2 equivalent thickness of 0.24 nm, dielectric dissipation factor less than 1%, and leakage current of about 40 nA/cm2 at ∓1.5 V.

(Ba,Sr)TiO3 Thin Films for Dram’s

“…The capacitance density is limited by ttXb: making it the most important factor in achieving a high capacitance density. The small interface capacitance reported by Kuroiwa et al [27] was not replicated by Hwang et al [26] even though the top and bottom electrode, deposition technique, substrate temperature and composition (BaiSr ratio) were nomin'ally identical.…”

“…C EoE Eo x 3.9 Figure 7 by Hwang et al [26] (sputtered BST with either 550°C or 750 °C post top electrode anneal) or for comparison by Kuroiwa et al [27] (sputtered BST at 660°C for with BaiSr ratio either 50/50 or 75/25). …”

“…An outstanding example of the capacitance density versus thickness for sputtered BST is shown in Figure 7 [26]. The best capacitance density measured to date is 0.24 nm teq, or 144 f}1/J.Ull2.…”

“…By annealing the BPSG at 800-850°C, local planarization occurs and the step between the cell array and the periphery becomes gradual. Unencapsulated BST has very little degradation after an 800°C 30 min N2 anneal [122,124] or even an 850°C 30 min N2 anneal [26]. Unfortunately, the use of a BPSG for local planarization results in poor leakage current [122,124].…”

Barium Titanate-Based Materials – a Window of Application Opportunities

“…As mentioned earlier, barium strontium titanate is an extensively investigated ferroelectric material due to its good electrical properties in bulk and thin film form being a leading candidate for applications in many electronic devices. Barium strontium titanate is currently considered as an attractive material in sensing, memory, capacitor and RF and microwave applications (Kirchoefer et al, 2002;Acikel et al, 2002;Hwang et al, 1995;Zhu et al, 2004;Tissot, 2003). But many important issues, such as improving dielectric constant values, dielectric loss and leakage, still need further attention in order to improve film quality and device performance.…”