Atomic layer deposition of aluminum phosphate layers using tris(dimethylamino)phosphine as P-precursor

Metal phosphates are gaining attention as versatile functional materials with a wide range of applications. Depositing these materials as thin conformal layers with atomic layer deposition requires a phosphorous precursor. Here, the use of tris(dimethylamino)phosphine (TDMAP) is explored by reporting the characterization of an aluminum phosphate process using TDMAP, the well-known aluminum precursor trimethylaluminum (TMA), and O2-plasma as precursors. Films grown with a four-step process (TDMAP–O2-plasma–TMA–O2-plasma) at 300 °C have a stoichiometry of Al1P0.51O2.9 and are amorphous, but do contain [PO4]3− units. Comparing the four-step process with three-step processes omitting one of the two O2-plasma steps provides insights into the reactivity of precursors. TMA is able to react with a TDMAP terminated surface but not vice versa. TDMAP has low inherent reactivity and requires the use of a coreactant to remove the ligands of the adsorbed TMA molecules and render the surface reactive for TDMAP adsorption. By implementing a supercycle approach using the (TDMAP–O2-plasma) sequence and the (TMA–O2-plasma) sequence as subcycles, more phosphorous rich films can be obtained. The phosphorous content of the deposited aluminum phosphate is shown to have a significant effect on its performance as a battery coating material.