In situ characterization of titanium silicide formation: The effect of Mo interlayer, temperature ramp-rate, and annealing atmosphere

Abstract

The formation of titanium silicides has been studied using simultaneous in situ x-ray diffraction with millisecond time resolution and sheet resistance measurements. The effect of a Mo interposed layer between Ti films and Si substrate was investigated by varying the thickness of the Mo interlayer from 0 (Ti/Si) to 1.8 nm (Ti/Mo/Si). The thickness of Ti was kept to 55 nm for all samples. Both isothermal annealing and ramp annealing in helium were performed in order to study the mechanism of silicide formation. While C49 TiSi2 was the only disilicide found after annealing Ti/Si at 650 °C for 20 min, C54 TiSi2 was readily formed in the presence of Mo. The formation of C49 TiSi2 was not observed with a 1.8 nm thick Mo interlayer. Instead, there was indication that C40 (Mo,Ti)Si2 was formed. In addition, broad diffraction peaks, weak in intensity, could be all assigned to Ti5Si4. However, the presence of Ti5Si4 alone did not induce the formation of C54 TiSi2. Even with a 20 °C increase in isothermal annealing temperature to 670 °C for 20 min, the presence of Mo was found to be a necessity for the formation of C54 TiSi2. When annealed in nitrogen, instead of helium, the formation of surface titanium nitride competes with the formation of silicides. The formation of C54 TiSi2 was even suppressed in the sample with a 1.8 nm Mo interlayer when annealed at 650 °C in nitrogen. The formation of Ti5Si4 and the role it plays in the formation of other silicides (C40, C49, and C54) are discussed on the basis of simple crystallographic considerations. The effect of a Mo interlayer and/or ramp-rate on the formation of C40 (Mo,Ti)Si2 and C49 TiSi2 is discussed in conjunction with variations of the preferential orientation of C54 TiSi2 films.