A new Au etch, recently developed for selective Au etching on Ti/Pt/Au metallization of optoelectronic devices, has been tested on Au wires bonded on Al films. Contrary to theoretical expectations, Au wires are removed without Al damage, except for a very localized area around the bond interface. The role of the native Al oxide is discussed in preserving Al and allowing Au lift off.

A specific problem in failure analysis of InGaAs/ AlGaAs laser diodes asked for a deprocessing tool able to selectively etch gold from a Ti/Pt/Au triple metal layer. Attempts made by the usual I2/KI etch confirmed the damage that it causes to the crystal stack, and non-uniform attack of gold. A new etch, indicated as Epta-Methyl-bis-diodine, has been successfully employed. Careful time control and detailed characterization of the complex metallization pattern of the devices allowed not only to properly expose the Pt layer, but also to preserve the overall electrical connection, thus maintaining the capability of both measuring the electrical characteristics at low current injection and collecting the EBIC signal from the etched device.