5.1 SCOPE OF THE CHAPTER

In this chapter, we present nickel silicide as the next material for contact to microelectronic CMOS devices. After briefly introducing the main advantages and challenges, we will describe the material properties of NiSi with an emphasis on characteristics that are different from the prior CoSi ₂ and TiSi ₂ contacts. Section 5.4 covers the in situ measurements of the phase formation sequence, putting emphasis on the presence of multiple metal-rich phases, on the very low formation temperature and on formation mechanisms. The following two sections (5.5 and 5.6) cover interesting properties of Ni monosilicide that are either new or hardly known in the microelectronics field, namely the large anisotropy in the thermal expansion and the unexpected texture in NiSi films formed on single crystal silicon. It is anticipated that the negative thermal expansion along one crystal axis together with the crystal alignments during NiSi formation (axiotaxy) will be of importance for the degradation of the film at high temperature. Section 5.7 covers thin film degradation at high temperature either through the formation of NiSi ₂ or through grain grooving and agglomeration. We also present several material improvements that have been reported to delay the degradation of films at higher temperature. The last section (5.8) contains some examples of electrical and physical characterisation from state-of-the-art devices.