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

The tungsten-stacked via structure will be widely used in future generation s of semiconductors to increase the density of aluminum wiring. One problem with this structure is that film separation is sometimes observed at the i nterface between the aluminum wiring and the oxide layer. This separation o ccurs only in the specific stacked via structure, and it carries a risk of a potential reliability of via open problem. Some experiments aimed at solv ing this separation problem revealed that the stress induced by insufficien t TiAl3 formation during the heat cycle of metal annealing is strongly rela ted to the film separation. The occurrence of the insufficient TiAl3 format ion is highly dependent on the condition of the interface between the titan ium 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 optimiz ed properly, the stress value of TiAl3 formation indicates the position of the maximum stress point during metal annealing. It was demonstrated that m onitoring of the maximum stress point is one method for determining whether the TiAl3 is fully formed.