As the evolution of microelectronics technology continues to target integrated circuit structures of reduced minimum feature size (line width), high integration density and higher signal processing speed, the flexibility (margin for error) of semiconductor wafer structure parameters has been reduced to the point where most, if not all, components have become constituent and dimension critical. For example, in semiconductor environments where signal processing speed and circuit robustness are important performance criteria, such as in very high speed integrated circuits, electroplated gold, which possesses superior conductivity and external influence immunity properties, has become the predominant choice for the interconnect medium.
The choice of gold electroplate for this purpose, however, is not without a price, as gold does not readily adhere to semiconductor (e.g. silicon dioxide) wafer structures and, consequently, requires the use of an adhesion layer such as titanium between the gold and the underlying material. As a further complication, when formed directly on the titanium layer, gold forms compounds that cannot be readily etched.
To remedy this problem the addition of a diffusion barrier of titanium nitride between the gold electroplate and the titanium layer, together with an additional barrier layer of platinum between the titanium nitride and the gold, has been suggested, as described in Fournier U.S. Pat. No. 3,879,746. In the environment to which the patented scheme is applied, the interconnect methodology involves beam lead structures in which the contact surface area of the interconnect metal and the photoresist used for its' patterning is considerably larger, and therefore less prone to delamination during plating, than the extremely narrow (sub micron) line widths of present day integrated circuit structures. Substitution of the platinum layer by a gold layer reduces the photoresist adhesion problem but introduces a loss of adhesion between the titanium nitride and the gold layers. It has been found that the titanium nitride layer employed in the patented laminate scheme does not possess the necessary adhesion strength to prevent a very narrow width noble metal layer from separating from the nitride layer when subjected to successive temperature cycles. While the adhesion mechanism is not entirely understood it is believed that the fact that the electroplated gold is tensile while the titanium nitride is compressive, together with the extremely narrow (quasi edge) contact area of the noble metal and the nitride, contributes to the tendency of the gold line to separate or peel away from the titanium nitride when subjected to repeated temperature cycling.