Sequential Infiltration Synthesis of Electronic Materials: Group 13 Oxides via Metal Alkyl Precursors

The sequential infiltration synthesis (SIS) of group 13 indium and gallium oxides (In2O3 and Ga2O3) into poly(methyl methacrylate) (PMMA) thin films is demonstrated using trimethylindium (TMIn) and trimethylgallium (TMGa), respectively, with water. In situ Fourier transform infrared (FTIR) spectroscopy reveals that these metal alkyl precursors reversibly associate with the carbonyl groups of PMMA in analogy to trimethylaluminum (TMAl), however, with significantly lower affinity. This is demonstrated to have important kinetic consequences that dramatically alter the synthetic parameters required to achieve material growth. Ab initio density functional theory simulations of the methyl methacrylate monomer with group 13 metal alkyls corroborate association energy that is 3× greater for TMAl than for either TMIn or TMGa. As a consequence, the kinetics of activated diffusion within the film is observed to be far more rapid for TMIn and TMGa than for TMAl. Spectroscopic ellipsometry and scanning electron microscopy, in combination with Hall effect measurements of SIS-derived In2O3 films, demonstrate that SIS enables rapid growth of thin films with continuous electrically conductive pathways after postannealing. Notably, SIS with TMIn and water enables the growth of In2O3 at 80 °C, well below the onset temperature of atomic layer deposition (ALD) using these precursors.