Comparative study of thermal behavior of a series beta-diketonate precursors for chemical vapor deposition of lithium-containing films

Abstract

Five volatile lithium beta-diketonates: Li(tmhd) (1), Li(pta) (2), LiL (3), LiLF (4), Li(tmha) (5) (tmhd = 2,2,6,6-tetramethyl-heptane-3,5-dionate, pta = 1,1,1-trifluoro-5,5-dimethyl-hexane-2,4-dionate, L = 2-methoxy-2,6,6-trimethyl-heptane-3,5-dionate, LF = 1,1,1-trifluoro-5-methoxy-5-methyl-hexane-2,4-dionate, tmha = 2,2,6,6-tetramethyl-heptane-3-imino-5-onate) and lithium alkoxide Li(OtBu) (6) were examined by combination of several complementary methods to study their thermal behavior in solid and gas phase and to check their suitability as precursors for chemical vapor deposition of Li-containing films. The best storage stability was observed for 3 and 4. Thermal gravimetric analysis and vacuum sublimation test were used to compare stability of the complexes under vaporization. In situ mass spectrometry was used to study the gas phase composition and the surface decomposition chemistry. Diketonate complexes 1, 3-5 passed into the gas phase as tetranuclear particles. Upon further heating, they split into binuclear species. The binuclear species thermolysis is responsible for the film deposition. The vapor thermal stability in oxygen increases in the row 3 > 1>5 > 2>4 > 6. CVD films obtained at 500 °C in the presence of oxygen using 1, 3 and 5 consisted of Li2CO3. LiF films can be obtained using 2, while 4 allow one to obtain the Li metal films in the oxygen presence on both Si and Pt/Si substrates.