Enhanced adhesion and thermal stability of Al/Cr film on indium-tin-oxide (ITO)-coated glass

Metallization of indium-tin-oxide (ITO)-coated glass using an Al/Cr composite thin film is a common practice for chip-on-glass packaging. However, the reliability of the Cr/ITO interface is always a problem because of poor adhesion due to the chemical inertness of ITO. In this study, the adhesion strength between a Cr film and ITO coated glass was enhanced by forming an intermediate oxide layer at the interface. To find out the optimal interface condition, various amounts of oxygen were doped at the interface. The results show that the adhesion strength and thermal stability are both enhanced by the interfacial doping of oxygen. This enhancement is found to be related to the flow rate of oxygen and, therefore, to the oxide thickness. Maximum improvement occurs when the flow rate of oxygen is set at 6 sccm during doping, and at this rate the interface oxide thickness also reaches its maximum value. Under this condition, the Cr/ITO interface also shows the best thermal stability. Wire bond testing shows that the wire pull strength is affected by the thickness of Al film. The results of this study show that the Al film should not be thicker than 1 μm.