(Beta)-Barium borate thin film formation on silicon through metal organic decompostion of two novel precursors, barium dimesitylborinate and barium (18-crown-6) Cyclotriboroxane

Two novel precursors, barium dimesitylborinate and barium (18-crown-6) cyclotriboroxane, were synthesized to produce thin films of p-barium borate (P-Ba3B60i2) via the metal organic decomposition (MOD) process. The two precursor reagents were characterized by nuclear magnetic resonance, infrared spectroscopy, differential thermal analysis (DSC), thermal gravimetric analysis (TGA), and elemental analysis. The MOD process was initially used to produce P-barium borate powders. The powders were heated for 1 hour under oxygen flow at various temperatures. The formation of p-barium borate was confirmed by powder X-ray diffraction of the products of thermolysis of both precursors, p-barium borate formation occurred at 800 C and 550 C for barium dimesitylborinate and barium (crown ether) cyclotriboroxane, respectively. Thin films of both precursor compounds were produced by a spin coating process. The substrates used were silicon wafers with a (100) orientation. Tetrahydrofuran was found to be a good solvent for the barium dimesitylborinate precursor. Ethanol was used for barium (crown ether) cyclotriboroxane. Again, the MOD process was used. The films were heated to various temperatures for various times under flowing oxygen. The films were then analyzed by thin film X-ray diffraction to determine if p-barium borate was formed. Due to substrate interaction thin films produced from the barium dimesitylborinate precursor did not contain P-barium borate. However, monophasic P-barium borate films were produced from heating the barium (crown ether) cyclotriboroxane precursor to temperatures between 600 and 700 C for 1 hour. The six membered anionic borate ring is the key structural unit in p-barium borate. Since the ring unit is already present in the barium (crown ether) cyclotriboroxane precursor lower temperature processing is needed, and substrate interaction becomes less likely. Ellipsometry was used to measure the index of refraction of the films. The index of refraction, measured by ellipsometry, was 1.51 for the film produced from barium dimesitylborinate. The index of refraction was 1.68 for the film produced from barium (crown ether) cyclotriboroxane.