Nickel silicides in semiconductor processing: thermal budget considerations

Abstract

Nickel silicide (NiSi) is emerging to be the choice material for contact application in semiconductor device processing for 65 nm technology node and beyond. However, process integration issues are yet to be completely understood and addressed. The focus of present work is to facilitate better understanding of the influence of thermal budget on nickel silicide solid-state reaction. The reaction couple consists of single-crystal silicon wafers with nickel layers deposited on them. Requirements for low temperature anneal and improved within wafer sheet resistance uniformity pose challenges for conventional lamp-based rapid thermal processing (RTP) due to lamp response effects on temperature controllability. Extendibility of such a system is presented with emphasis on process chamber technology. Low temperature “spike” anneal is demonstrated for temperatures <250 °C. Evolution of the nickel-rich silicide phase as a function of temperature is recorded using X-ray reflectance (XRR) and X-ray diffraction (XRD) techniques. Crystallographic orientation of Ni 2Si changes as a function of thermal exposure during the first anneal step; this plays an important role in determining the thermal stability of the low resistance mono-silicide during integration. It is postulated that lowering the Ni 2Si/Si interface energy favors the delay (in temperature) of the agglomeration of the NiSi. RTP performance stability of less than 1 °C is presented for a sub-300 °C process. Understanding and resolving the issues around process monitoring methodologies for low temperature anneal are important. The ability to monitor the total thermal exposure down to sub-200 °C regime may be necessary for successful integration of nickel silicide in device manufacturing flow.