LS-MOCVD of BSTO Thin Films Using Novel Ba and Sr Precursors
- PDF / 112,076 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 170 Views
D3.22.1
LS-MOCVD of BSTO Thin Films Using Novel Ba and Sr Precursors Hyun Goo Kwon, Youngwoo Oh, Jung Woo Park, Young Kuk Lee, Chang Gyoun Kim, Yunsoo Kim Thin Film Materials Laboratory, Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejeon 305-600, Korea ABSTRACT We report the synthesis of new precursors Ba(thd)2(tmeea) and Sr(thd)2(tmeea), where tmeea = tris[2-(2-methoxyethoxy)ethyl]amine, and the LS-MOCVD of barium strontium titanate (BSTO) thin films using these precursors. Thin films of BSTO were grown on Pt(111)/SiO2/Si(100) substrates by LS-MOCVD using the cocktail source consisting of the conventional Ti precursor Ti(thd)2(OiPr)2 and the new Ba and Sr precursors. As-grown films were characterized by SEM, XRD, XRF, and C-V measurement. BSTO films grown at 420 °C were stoichiometric barium strontium titanate with very smooth surface morphology and their dielectric constants were found to be as large as 320. The dependence of composition, microstructure and the electrical properties of the BSTO films on the growth temperature, annealing temperature, and working pressure will be discussed. INTRODUCTION Dynamic random access memory (DRAM) capacitor technology faces a new challenge of introducing new storage capacitors due to the drastic increase of memory density. There are two different solutions to overcome the challenge, one is to explore a new material with high dielectric contant and low leakage current including barium titanate and the other is to change the structure of DRAM itself [1]. Barium strontium titanium oxide (BSTO) has widely been studied as one of promising candidate materials for multi-giga bit DRAM capacitors from the late 1980s’ [2]. BaTiO3 and SrTiO3 form a complete solid solution, resulting in BaxSr1-xTiO3, in the whole range of Ba composition (0 ≤ x ≤1) and there is morphotrophic phase transition from tetragonal to cubic structure when x is larger than 0.7. The dielectric constant of BSTO is known to increase from several hundreds to several thousands with the increase of Ba composition. Thin films of BSTO have been fabricated with techniques such as rf-sputtering [3], laser ablation [4], sol-gel process [5], and metalorganic chemical vapor deposition (MOCVD) [6]. For the successful fabrication of BSTO thin films by MOCVD, however, each precursor should have not only high volatility but also an extended chemical or thermal stability at the vaporization temperature. In addition, the precursors should decompose completely at the deposition temperature in order to avoid carbon incorporation in the film. Conventional Ba and Sr precursors for BSTO thin films are β-diketonate complexes, such as M(thd)2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) and M(hfac)2 (1,1,1,5,5,5-hexafluoro-2,4-pentanedionate) [M = Ba and Sr]. Although M(hfac)2 has good volatility at low temperatures in comparison with M(thd)2, metal fluorides such as BaF2 and SrF2 with low dielectric constants remain in the thin films. M(thd)2 precursors sublime around 200 °C and decompose around thei
Data Loading...
