Chemically Conformal ALD of SrTiO[sub 3] Thin Films Using Conventional Metallorganic Precursors

Abstract

SrTiO 3 ͑STO͒ thin films were grown on Si wafer, Pt-and Ru-coated Si wafers, respectively, by an atomic layer deposition ͑ALD͒ technique using conventional metallorganic precursors, Sr͑C 11 H 19 O 2 ͒ 2 ͑Sr͑thd͒ 2 ͒ and Ti͑Oi-C 3 H 7 ͒ 4 ͑TTIP͒ as Sr-and Tiprecursors, respectively, with a remote-plasma activated H 2 O vapor as the oxidant at a wafer temperature of 250°C. Patterned Si wafers with contact holes having a diameter of 0.13 and 1 µm depth ͑aspect ratio of 8͒ was used in order to test the film-thickness and cation-composition conformalities over the contact hole surface. The ALD behavior of the STO film was critically dependent on the Sr͑thd͒ 2 source heating temperature. When the Sr source temperature was Ͻ ϳ200°C ͓Sr͑thd͒ 2 melting temperature͔ stoichiometric STO films were deposited with a good process reliability. Excellent film thickness and cation composition conformalities ͑nonuniformity Ͻ3%͒ over the severe contact hole structure were obtained by the optimized precursor supply and deposition conditions. It was also observed that most of the input TTIP precursor molecules did not chemically adsorb on the SrO surface, possibly due to oversaturation of the SrO surface by the Sr͑thd͒ 2 molecules or thermally modified Sr͑thd͒ 2 molecules as a result of the heating process of the Sr͑thd͒ 2 when the Sr-source temperature was Ͼ ϳ200°C. This difficulty resulted in a nonuniform cation composition ratio along the contact hole.High-dielectric constant thin films such as SrTiO 3 ͑STO͒ and ͑Ba,Sr͒TiO 3 ͑BSTO͒ 1-5 have attracted great interest as the capacitor dielectrics of dynamic random access memory ͑DRAM͒ devices. Recently, these materials have also been actively studied for the high-frequency tunable devices, 6,7 decoupling capacitors, 8 and gate dielectric 9,10 applications. Among these, the DRAM capacitor applications require conformal deposition over a 3-dimensional structure with a feature size Ͻ0.1 m in terms of film thickness and composition, which is not required in other applications.The low-temperature ͑Ͻ500°C͒ metallorganic chemical vapor deposition ͑MOCVD͒ process has been extensively studied for producing STO and BSTO thin films for DRAM applications due to its good film step coverage over a severe 3D surface topology, and nondamaging deposition on the underlying electrode stack. 11,12 However, conformal deposition over the entire surface area of such an extreme geometry in terms of the chemical composition as well as the thickness has not necessarily been confirmed even for lowtemperature MOCVD processes. The authors have reported extensive experimental results on the composition and thickness variations of the MOCVD STO and BSTO films deposited at wafer temperatures ranging from 420 to 440°C on a capacitor hole pattern with dimensions of 0.15 ϫ 0.40 ϫ 0.57 ͑depth͒ m 3 where two shower-head-type and one dome-type MOCVD chamber with two different precursor sets were used. 13,14 From the study, it was found that obtaining a conformal composition and film thickness over the 3D geometry using th...

Band Engineering of Ru/Rutile-TiO2/Ru Capacitors by Doping Cobalt to Suppress Leakage Current

“…There are peaks that originated from Ru-O bonding as well as Ru-Ru bonding. Furthermore, we can identify RuO 2 16 from the shift in these peaks. Thus, we found that RuO 2 was formed at the surface of the Ru electrode.…”

“…• C, the vapor pressures of strontium such as Sr(thd) 2 are insufficient being less than 1 Torr. 2 Therefore, it is still difficult to commercialize SrTiO 3 .…”

“…2 Therefore, it is still difficult to commercialize SrTiO 3 . However, there are precursors of TiO 2 such as titanium tetraisopropoxide (TTIP) that have vapor pressures higher than that of strontium.…”

Synthesis of Heteroleptic Strontium Complexes Containing Substituted Cyclopentadienyl and β-Diketonate Ligands

“…The most common volatile precursors of strontium were synthesized using β-diketonates like 2,2,6,6-tetramethyl-3,5-heptanedione 7,8 and highly substituted cyclopentadienes.…”

Growth and thermal oxidation of Ru and ZrO2 thin films as oxidation protective layers

“…86 Oxygen transport studies have also been reported for Pt and Re protective layers, considered also as bottom gate electrodes for MOS-like devices. 87,88,89 In the case of gate dielectric layers for CMOS and memory (DRAM) devices, several (usually high-K) binary oxides such as Ta2O5, 90,91 Y2O3, 92,93 Al2O3, 91,94,95,96 HfO2, 97,98,99,100 ZrO2, 34,101,102,103 and TiO2, 104,105,106 and also perovskite materials such as SrTiO3 and (Ba,Sr)TiO3 have been investigated, 107,108 according to their electrical and/or other physical properties after/or during growth. Apart from the characterization of the grown layers, in some of these oxide studies, oxygen diffusion through the gate dielectric towards deeper layers has also been investigated.…”