High-reliability tungsten-stacked via process with fully converted TiAl3 formation annealing

The tungsten-stacked via structure will be widely used in future generations of semiconductors to increase the density of aluminum wiring. One problem with this structure is that film separation is sometimes observed at the interface between the aluminum wiring and the oxide layer. This separation occurs only in the specific stacked via structure, and it carries a risk of a potential reliability of via open problem. Some experiments aimed at solving this separation problem revealed that the stress induced by insufficient TiAl₃ formation during the heat cycle of metal annealing is strongly related to the film separation. The occurrence of the insufficient TiAl₃ formation is highly dependent on the condition of the interface between the titanium and aluminum, and it is also dependent on the ambient gas used for the ramp-up step in the metal annealing process. If these processes are optimized properly the stress value of TiAl₃ formation indicates the position of the maximum stress point during metal annealing. It was demonstrated that monitoring of the maximum stress point is one method for determining whether the TiAl₃ is fully formed