Takuji Hosoi

Formation Kinetics and Work Function Tuning of Pd2Si Fully Silicided Metal Gate

The formation kinetics of Pd2Si for fully silicided (FUSI) gate formation and the work function tuning of a Pd2Si FUSI gate by impurity predoping were investigated. It has been found that the morphology and phase of a formed FUSI layer depend not only on the silicidation annealing temperature but also on the heating ramp-up rate and the presence of impurities. Fast ramp-up annealing was necessary to avoid defect formation, such as voids in the silicide film at the oxide interface, and to obtain a homogeneous silicide film containing only Pd2Si phase. The most severe effect on the silicidation reaction, that is the increase in defect formation, was brought about by As predoping. The work function of the Pd2Si FUSI gate was modulated by impurity pileup at the Pd2Si/SiO2 interface, as in the case of the NiSi FUSI gate. However, the work function shifted in the opposite direction to that of the NiSi FUSI gate for As, P, Sb, and BF2. A wide range of work function shift, comparable to that of the NiSi FUSI gate, has been obtained for a Pd2Si FUSI gate.

Photoemission study of fully silicided Pd2Si gates with interface modification induced by dopants

Work function shifts for fully silicided (FUSI) Pd2Si gates with BF2 and P predoping, originally observed as the flatband voltage shifts in metal-oxide-semiconductor (MOS) diodes, were also reproducible for backside x-ray photoelectron spectroscopy measurements. The Pd composition ratios of FUSI layers were reduced in the vicinity of the gate SiO2 layer, which directly affects apparent work function in the MOS system. However, other non-negligible changes, such as pileup of predoped elements and Pd precipitation, were also found for the predoped cases. The work function shift by predoping should be considered to be a result of interaction of such multiple factors.

Characterization of Sb-Doped Fully-Silicided NiSi/SiO/sub 2//Si MOS Structure

X-ray photoelectron spectroscopy (XPS) measurement of Sb-doped fully-silicided (FUSI) NiSi/SiO2 interface has been carried out to evaluate location of Sb pileup and to discuss its role for workfunction shift. The XPS result revealed Sb encroachment into SiO2. Workfunction characterization by XPS implied that NiSi workfunction was identical to its original value without Sb pileup located inside the gate oxide. The impact of predoping on silicidation reaction was also investigated.

Importance of heat-up ramp rate for palladium-silicide fully-silicided-gate structure formation

Silicidation process for fully-silicided (FUSI) Pd2Si gate formation has been investigated. Two types of heating equipment was used for siliciding palladium deposited on a poly-Si/SiO2/Si MOS structure. One is lamp heating in a sputtering chamber and another is hot-plate heating. The former provide slower heat-up ramp because of relatively large thermal capacity. In this case, metal-rich phase was formed in the first stage of silicidation and it changed to Pd2 Si phase by additional heating after completion of silicidation reaction. FUSI utilizes impurity pre-doping to poly-Si to modulate workfunction. Pre-doping to poly-Si sometimes resulted in needle structure formation on a top of silicided film and voids at the interface between silicide and SiO2. These defects were reduced by silicidation with hot plate heating. In addition, Pd2 Si phase was obtained at the early stage of silicidation. Palladium and silicon reacts even at temperatures lower than 250degC. Therefore, in the case of the lamp heating, silicidation during heating is not negligible. These results are explainable considering change of major diffusion species during silicidation