Lithium phosphate, Li3PO4, has been considered a potential electrolyte material for lithium ion batteries and CO2 sensors in particular if the films can be made dense and of high quality already at low thickness. In this work, Li3PO4 thin films were deposited by atomic layer deposition (ALD) between 225 and 350 degrees C using trimethyl phosphate and either of the two lithium sources, namely lithium hexamethyldisilazide or lithium tert-butoxide. The deposited films showed slightly crystalline Li3PO4 structure in X-ray diffraction and the elastic recoil detection analysis confirmed this stoichiometry with some carbon and hydrogen impurities. The crystallinity and thermal stability of the films at elevated temperatures in N-2 were also examined. The long term stability of the deposited Li3PO4 films under ambient air may be an issue for the applicability of these processes.