With a semiconductor device having a multi-layer wiring structure, the diffusion of copper to the interlayer dielectric film is prevented by forming a barrier film, which is made from tantalum or the like, below the copper wiring This kind of tantalum barrier film is generally formed by sputtering a tantalum target.
In recent years, in line with the advancement of miniaturization of the wiring pursuant to the higher level of integration of semiconductor devices, there are demands for forming a barrier film with a uniform film thickness on narrow wiring grooves or fine via holes, and additionally demanded is the reduction in the variation of the resistance value (sheet resistance value) of the barrier film associated with the foregoing miniaturization.
A tantalum target is generally produced as follows; specifically, an ingot or a billet obtained by subjecting a tantalum raw material to electron beam melting and casting is forged, annealed, rolled, heat-treated, and subject to finish processing. Here, the following techniques are known in relation to a tantalum target and a production method thereof.
For example, Patent Document 1 describes that, by producing a tantalum target comprising a crystal structure in which the crystal orientation positioned at the center plane of the target is preferential to (222), it is possible to improve the structure of the crystal orientation of the target, improve the uniformity of the film upon performing sputtering, improve the quality of sputter deposition, and considerably improve the production yield.
Patent Document 2 describes that, by producing a tantalum target in which the area ratio of crystals having one orientation among (100), (111), and (110) does not exceed 0.5 when the sum of the overall crystal orientation is 1, it is possible to achieve superior deposition characteristics such as increased deposition rate, improved film uniformity, and lower generation of arcing and particles, and further possible to achieve favorable utilization efficiency of the target.
Patent Document 3 describes that, by adopting a production method including the step of clock-rolling a metal material, it is possible to reduce the texture band, and obtain a grain structure that is uniform across the entire surface and thickness of the metal material. Patent Document 3 further describes that the true strain resulting from the forging process can be made to be approximately 0.75 to approximately 2.0.