Interfacial reactions between WNx and poly Si1−xGex films

Abstract

The interfacial reactions at the WNx/poly Si interface and at the WNx/poly Si0.4Ge0.6 interface with the annealing conditions were investigated using high resolution transmission electron microscope (HR-TEM) and x-ray photoelectron spectroscopy (XPS). In the WNx/poly Si system, after a short period of annealing, an island-type precipitation was clearly observed under the Si–N layer, which was formed between WNx and poly Si. HR-TEM image and XPS analysis indicated that the island-type precipitation is composed of W, Si, and N. With increasing annealing time, the Si–N layer became thinner and island-type precipitation became continuous layer. However, in the WNx/poly Si0.4Ge0.6 system, the formation of precipitation was obviously prevented after annealing and the island-type precipitation remained between the WNx films and the poly Si1−xGex films in spite of long time annealing. These results are attributed to the fact that the Si in poly Si0.4Ge0.6 reacts preferentially with N, produced in the decomposition of WNx films, due to lower Gibbs free energy of the Si compound than the Ge compound and unreacted Ge atoms accumulate at the WNx/poly Si1−xGex interface.