Study of bismuth alkoxides as possible precursors for ALD

Abstract

While searching for bismuth precursors for thin film preparation by atomic layer deposition (ALD) three bismuth alkoxides Bi(O^tBu)₃ (1), Bi(OCMe₂ⁱPr)₃ (2), Bi(OCⁱPr₃)₃ (3), bismuth β-diketonate, Bi(thd)₃ (4), and bismuth carboxylate, Bi(O₂C^tBu)₃ (5), were synthesized and evaluated. The compounds were characterized by CHN, NMR, MS, and TGA/SDTA. Earlier unknown crystal structures of compounds 1 and 3 were solved. Compound 1 forms dimeric and loose polymeric structures in the solid state while 3 is strictly monomeric. For compound 2 crystals suitable for complete structure solution could not be grown. Crystallization trials of 2 from hexane and toluene resulted in oxygen bridged tetramer [Bi₂O(OCMe₂ⁱPr)₄]₂ (6). Compound 4 has dimeric structure and compound 5 forms loose tetramers as reported earlier. The structure of toluene solvated crystal [Bi(O₂C^tBu)₃]₄·2MeC₆H₅ (7) was solved. All compounds studied showed relatively good volatility and thermal stability. They were all tested in ALD deposition experiments, in which compound 2 was found to be the most suitable for ALD growth of Bi₂O₃. It exhibited a clear improvement over Bi precursors studied earlier.