SilicideTechnology for Integrated Circuits
This detailed text provides guidance on the development and application of metal silicide technology as it emerges from the scientific to the prototype and manufacturing stages.
TABLE OF CONTENTS SilicideTechnology for Integrated Circuits
5.7: HIGH TEMPERATURE LIMITATIONS
5.7 HIGH TEMPERATURE LIMITATIONS
The initial sections of this chapter described the properties, the formation mechanisms and characteristics of Ni silicide phases that are stable at room temperature. As the low resistivity monosilicide phase is the relevant one for microelectronics applications, the unexpectedly large anisotropy in the thermal expansion and the texture of films were carefully analysed in Sections 5.5 and 5.6. The current section deals with the degradation of NiSi films at high temperature. It is crucial for the film to retain its integrity and low resistance to as high a temperature as possible to allow for further anneals after silicide formation. There are two mechanisms by which the NiSi film can degrade at high temperature. In the first one, the NiSi film transforms to NiSi 2. In the second one, the film suffers morphological degradation through grain boundary grooving and agglomeration.
5.7.1 Formation of NiSi 2
As can be seen on the Ni/Si phase diagram (FIGURE 5.1), the NiSi phase is not at equilibrium with Si. At high temperature, it is expected that the NiSi film will react with Si to form NiSi 2. Fortunately, the ? H for the reaction of NiSi and Si is very small resulting in a high nucleation barrier for the formation of NiSi 2. This formation is observed with XRD in FIGURES 5.4 and 5.5 through the appearance of the NiSi 2(220) diffraction line at about 800 C. The sudden appearance of the phase at high temperature is...
Copyright The Institution of Electrical Engineers 2004 under license agreement with Books24x7
