1. Field of the Invention
This invention relates to a method for forming a titanium nitride (TiN) barrier layer having a (111) crystallographic orientation on an integrated circuit structure.
2. Description of the Related Art
In the formation of integrated circuit structures, aluminum is used for forming the electrical connections or wiring between active and/or passive devices comprising the integrated circuit structure. Conventionally this involves the use of aluminum which is electrically connected to underlying silicon in the structure. While the aluminum and silicon are electrically connected together, it has become the practice to use intermediate electrically conductive layers interposed between the silicon and aluminum to respectively provide better electrical connection to the silicon, and to provide a physical (metallurgical) barrier between the silicon and aluminum to prevent spiking of the aluminum into the silicon, i.e., migration of aluminum atoms into the underlying silicon, which can interfere with the performance and reliability of the resulting integrated circuit structure.
Conventionally, one method which has been used to accomplish this has been to deposit a layer of titanium over a silicon surface, e.g., to form a with the silicon, and then to anneal the titanium-coated structure in the presence of nitrogen whereby a titanium silicide layer forms over the exposed silicon to form a good electrical contact with the silicon and titanium nitride forms over the titanium silicide as the surface of the titanium layer reacts with the nitrogen atmosphere.
While this method does accomplish the formation of a good electrical contact to the silicon, by formation of the titanium silicide, it often does not result in a satisfactory formation of a barrier layer of titanium nitride over the titanium silicide. This is because the simultaneous formation of both the titanium silicide and the titanium nitride from the same titanium layer results in competing reactions wherein more of the titanium reacts with the silicon, resulting in the formation of a layer of titanium nitride of insufficient thickness to provide the desired barrier protection against aluminum spiking.
One prior art solution to this problem has been to form the titanium silicide barrier layer first and then to sputter additional titanium nitride over the titanium silicide or titanium silicide/titanium nitride layer. In this way a sufficient thickness of titanium nitride may be formed to provide the desired barrier layer.
While the above method results in satisfactory formation of a titanium silicide contact layer and a titanium nitride barrier layer over the silicide, and beneath the subsequently deposited aluminum, an problem has been encountered involving electromigration of aluminum atoms in the aluminum layer, during subsequent operation of the integrated circuit structure, if the aluminum layer is not formed with a (111) crystallographic orientation. Such electromigration of the aluminum atoms can result in open circuits in the integrated circuit structure and, therefore, such electromigration must be inhibited or eliminated.
Formation of titanium nitride by the nitration of titanium will result in formation of a titanium nitride layer having a (111) crystallographic orientation. However, as discussed above, formation of such a titanium nitride from titanium deposited over silicon does not result in formation of a sufficiently thick titanium nitride barrier layer.
Conversely, while sputter deposition of titanium nitride will form the desired thickness of titanium nitride barrier layer, the crystallographic orientation of sputtered titanium nitride is usually either (200) or polycrystalline.
It would, therefore, be desirable to form a titanium nitride barrier layer over a silicon surface with a titanium nitride surface having a (111) crystallographic orientation, whereby spiking of aluminum through such a titanium nitride layer would be inhibited or eliminated, yet the formation of aluminum of (111) crystallographic orientation would be promoted by the nucleation sites provided by the (111) crystallographic orientation of the underlying titanium nitride surface.