Metallorganic Chemical Vapor Deposition of Sr-Ta-O and Bi-Ta-O Films for Backend Integration of High-k Capacitors

Abstract

Dielectric layers with high dielectric constant, low leakage, and high breakdown strength are of great interest for application in devices such as Dynamic random access memory, decoupling capacitors, or impedance matching capacitors. However, some applications require complementary metal oxide semiconductor backend integration of those capacitors, with low-temperature processing. In this work, we prepare Pt/Sr-Ta-O/Pt and Pt/Bi-Ta-O/Pt capacitors on silicon, where dielectrics are deposited at 360°C by metallorganic chemical vapor deposition ͑MOCVD͒. After capacitor fabrication, a minimal leakage is obtained for a recovery anneal at a temperature of 500°C for Pt/Sr-Ta-O/Pt and 300°C for Pt/Bi-Ta-O/Pt. We show that both types of dielectrics are promising for incorporation in backend integrated high-k capacitors. Particularly, their leakage level is lower than reported for other dielectrics, which constitutes a significant advantage for memory application. The results also suggest that MOCVD is a suited technique to obtain very thin Sr-Ta-O and Bi-Ta-O films which are dense, smooth, and with good interfacial quality.Dielectric layers with high dielectric constant, low leakage, and high breakdown strength are of great importance and have a wide range of applications in semiconductor devices. High-k dielectrics are being extensively developed for gate dielectric replacement in complementary metal oxide semiconductor ͑CMOS͒ technology, as well as for application in dynamic random access memory ͑DRAM͒. In the latter case, capacitance densities of 10 F/cm 2 together with low leakage ͑Ͻ10 −9 A/cm 2 ͒ are attainable using thin crystalline films prepared by metallorganic chemical vapor deposition ͑MOCVD͒. 1 However, that approach requires process temperatures exceeding 500°C, which is not suitable for integrated passive applications. The need for high capacitances integrated in the wiring level of circuitry is increasing. For example, decoupling capacitances are needed on logic integrated circuits for high-frequency operation to decrease the inductance between the source of charge and the clocking transistor, while application-specific integrated circuits ͑ASIC's͒ used in radio-frequency applications require high capacitances with low loss for impedance matching. 2 Some ASIC's also need memories having high capacitance and low leakage integrated in the upper wiring layers. For those applications, process temperatures should be lower than 400°C if Cu/low k interconnects are used.Several materials such as Al 2 O 3 , 3,4 Ta 2 O 5 , 5-7 ZrO 2 , 8 Y 2 O 3 , 9 or HfO 2 ͑Ref. 10͒ have been recently studied for these applications. In the present work, we investigate the electrical properties of metalinsulator-metal ͑MIM͒ capacitors using Sr-Ta-O and Bi-Ta-O dielectrics that are deposited by MOCVD as amorphous layers on Pt substrates at 360°C. We discuss their advantages over other materials and their potential applications. ExperimentalThe capacitors were realized as follows. The Pt bottom electrode was sputtered on an IrO 2 /Ir/Ti...

Nonlinear capacitance variations in amorphous oxide metal-insulator-metal structures

“…This force enhances the restoring force, which decreases the entropy and dielectric susceptibility. [21][22][23] In conclusion, we have derived analytical expressions to explain capacitance variations with applied electric field and temperature ͑quadratic V cc and T cc ͒ for amorphous oxidebased MIM capacitors. Model predictions were consistent with experimental CV data for many amorphous oxides, SiO 2 included.…”

High performance metal-insulator-metal capacitor using a SrTiO3/ZrO2 bilayer

“…Therefore, the traditional dielectrics, SiO 2 and Si 3 N 4 , were forsaken because of their low dielectric constant ͑ Ͻ 10͒ and there is a lot of ongoing effort to develop high-materials ͑ Ͼ 15͒ such as Ta 2 O 5 , HfO 2 , and ZrO 2 , to name a few. [1][2][3][4][5][6][7][8][9][10] An important issue regarding capacitor performances is the voltage linearity, which shows the dependence of capacitance ͑C͒ on the applied bias ͑V͒. For high-oxides it is usual to observe a quadratic voltage dependence of capacitance, ͓C͑V͒-C 0 ͔ / C 0 = ␣V 2 + ␤V, where C 0 is the capacitance at zero bias, and ␣ and ␤ are the quadratic and linear coefficients.…”

“…For most of the high-dielectrics the coefficient ␣ is in the 100-1000 ppm/ V 2 range and the coefficient ␤ is in the 100 ppm/V range. [1][2][3][4][5][6][7][8][9][10][11] As a consequence, for usual working voltages ͑1-3 V͒ the quadratic contribution prevails ͑␣V 2 Ͼ ␤V͒ and the most important parameter that must be controlled is the quadratic coefficient ␣. Usually ␣ is observed to increase dramatically with decreasing oxide thickness.…”

Investigation of the leakage mechanism in Sr–Ta–O and Bi–Ta–O thin film capacitors

“…Figures 3͑a͒ and 3͑b͒ show the current density as a function of the field measured at 25°C respectively for BT and ST capacitors having different dielectric thicknesses. 2 The absence of leakage increase for a given field with the thickness decrease down to 20 and 15 nm for BT and ST capacitors, respectively, suggests that the field is uniformly distributed in the film thickness and that the bands are straight, confirming in turn excellent insulating properties. On the other hand, in the nonlinear region the leakage is clearly field dependent whatever the BT thickness down to 20 nm ͓Fig.…”