Conventional semiconductor processing requires patterning of an aluminum or aluminum alloy layer to define conductors, referred to as interconnect lines, between various locations on the device. In order to define the interconnects, a photosensitive organic polymer layer referred to as the photoresist layer is applied over the aluminum and selectively hardened by photolithographic techniques. The non-hardened areas are then removed by selective solvents, forming a desired pattern in the photoresist layer. The exposed portions of the aluminum layer are then etched, typically using a liquid etchant or chlorine plasma, to define the interconnect lines. Often, a layer of titanium-tungsten is provided intermediate the aluminum and silicon layers to prevent migration of the aluminum into the silicon.
The titanium-tungsten layer must be patterned corresponding to the overlying aluminum layer, typically by etching with a liquid oxidant such as hydrogen peroxide. A problem arises, however, due to the fact that chlorides remain on the semiconductor wafer surface as by-products of the plasma aluminum etch process. These chlorides cause the aluminum to be prone to corrosion in air and in chemical environments (e.g., during subsequent etching steps). Corrosion of the aluminum can result in immediate electrical failure of the device or cause long-term reliability problems due to failure of the device after it has been in operation for some time.
For these reasons, it would be desirable to provide a convenient method which would allow completion of the interconnect process through wet etching of the titanium-tungsten layer without corrosion of the aluminum leads.