A Study on the Thermal Decomposition of Ba(tmhd) 2 and Sr(tmhd) 2
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ABSTRACT Decomposition of Sr(tmhd) 2 and Ba(tmhd) 2 was investigated by thermogravimetric analysis, in-situ FTIR, and mass spectrometry. Both compounds decomposed following 3 steps: 1) decomposition of the ligands, 2) simultaneous vaporization and partial decomposition of metal-organics, and 3) decomposition of the vaporized metal-organics which existed as the oligomenic species. The Sr source decomposed at lower temperatures and in a narrower temperature range than the Ba source. Also, the gaseous oligomeric species from the Sr source decomposed relatively quickly while the corresponding species from the Ba source decomposed slowly over a long period. Such a difference between the two compounds is due to different bond energies between the metal atom and the ligands, as indicated by our FTIR results.
INTRODUCTION Ferroelectric thin films of barium strontium titanate (BSI) oxides have a potential of application to capacitor for 256Mb and 1Gb dynamic random access memory[l]. Sol-gel, RF-sputtering, co-evaporation, and metal-organic chemical vapor deposition(MOCVD) are investigated as growth techniques for the BST films. Among them, MOCVD attracts much attention because it is the most versatile technique to obtain films of different compositions, thicknesses, and a good step coverage[2]. But a major obstacle to application of the MOCVD method is difficulty in controlling the composition of the
high-dielectric materials[3,4]. To control the fihbn composition, it is necessary to understand the decomposition mechanism of the metal organic sources. In this study, we have investigated then-nal decomposition of Ba(tmhd) 2 (tmhd: 2,2,6,6-tetrarnethyl-3,5-heptadione, (CH 3)3CCOCHCO(CH 3)3) and Sr(tmhd) 2 using thermogravimetry, mass spectroscopy and in-situ FTIR. Steps of the MO compound decomposition have been proposed based on the experimental results.
EXPERIMENTAL Sr(tmhd) 2 and Ba(tmhd)2 were purchased from STREM Chemicals. Thermogravimetry(TG), mass spectroscopy(MS) and infrared spectroscopy(IR) were the experimental methods used to observe the decomposition properties of Sr(tmhd) 2 and Ba(tmhd) 2. Among them, TG is useful for studying volatility and reactivity of the solid compounds, MS for analyzing the gaseous species, and IR for observing changes in specific bonds of both the solid and gas compounds. For temperature-programmed decomposition of the MO compounds, the samples were heated at 10°C/min and the decomposition products in the gas phase were analyzed with a mass spectrometer(JEOL, JMS-AX505WA). The solid and gas compounds were also analyzed by in-situ FTIR(Jasco, FT/IR-300E). The in-situ IR cell was made of an 1-inch O.D. quartz tube. Commercial stainless-steel unions were used to attach KBr windows at 161 Mat. Res. Soc. Symp. Proc. Vol. 415 0 1996 Materials Research Society
both ends of the quartz tube. The IR cell containing the sample disk made by pressing the powder mixture of KBr and the MO compounds could be evacuated to 10-3 Torn and heated up to 800'C.
RESULTS TGA Fig. 1 shows the weight loss of
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