The interface between sputter-deposited gold thin films and ion-bombarded sapphire substrates

Abstract

Pull-tests show that the adhesion strength of gold film sputter-deposited onto annealed and pre-sputtered sapphire is over 15 times higher than that of the film deposited onto as-received sapphire. The effects of ion beam bombardment on the sapphire substrate were investigated in situ with AES. Metallic aluminum was detected on the surface of sapphire substrates after irradiating for 3 min with 7 keV Ar+-ions. These results agree with TRIM calculations that yield preferential ion-beam etching. No metallic aluminum was formed at the surface when the ion bombardment was done at 3 keV for 3 min. The Au/Al2O3 interface was investigated using a new technique that takes advantage of the variable film thickness in the vicinity of a sputter-etched crater. This method not only allows for a non-destructive search of the interface but it also avoids a substantial ion damage to this region. Higher energy Auger peaks, which have higher Auger electron escape depth, revealed that a Au-Al-O compound formed at the interface. Formation of this compound, which is responsible for the strong metal-ceramic bonding, is due to ion-induced cleaning and reduction of the sapphire surface prior to gold film deposition.