Comparison of the diffusion barrier properties of tungsten films prepared by hydrogen and silicon reduction of tungsten hexafluoride

Abstract

We have made a comparative study of the thermal stability with respect to aluminum and silicon of tungsten films prepared by two different chemical vapor deposition processes. The first set of films were prepared via the direct reduction of WF6 by the silicon substrate whereas the second set were deposited by hydrogen reduction of WF6. The latter layers have a metallurgical behavior comparable with that of tungsten films deposited by other techniques while the former exhibit a very high thermal stability with no reactions between tungsten and aluminum or silicon detected up to temperatures as high as 625°C. This results from the high oxygen content of these films which allows the formation of interfacial oxides and thereby inhibits further interreactions. In the absence of oxygen, the barrier begins to fail at 550°C, leading eventually to the formation of a hexagonal silicide structure of the form W(Si,Al)2. The role of aluminum in enhancing the formation of the silicide and the nature of the hexagonal aluminum-containing silicide are discussed in some detail. © 1989.