A method of forming a passivation layer on a substrate includes providing a substrate in a processing chamber. The substrate includes a metallic surface which is a copper, tin or silver surface, or an alloyed surface of one or more of copper, tin or silver. The method further includes depositing at least one organic layer onto the metallic surface by vapour deposition, the organic layer formed from an organic precursor. The organic precursor includes a first functional group including at least one of oxygen, nitrogen, phosphorus, sulphur, selenium, tellurium, or silicon, and a second functional group selected from hydroxyl (—OH) or carboxyl (—COOH). The first functional group is adsorbed onto the metallic surface. The method further includes depositing at least one inorganic layer onto the organic layer by vapour deposition, wherein the second functional group acts as an attachment site for the inorganic layer.