Effects of Ti Interlayer on Ni/Si Reaction Systems

Abstract

The effects of Ti interlayer on the formation of Ni silicides on Si͑100͒ substrate was investigated. The phase and microstructure of Ni silicides during isochronal annealing treatment are monitored in situ by curvature measurement and characterized ex situ by other measurements. The addition of a thin Ti layer which formed an amorphous layer with the Si substrate acted as a diffusion barrier for the Ni atom in the early phase transformation process. The transformation temperature for the NiSi is significantly increased in an isochronal annealing process. When the NiSi phase is formed, the Ti-related layer moves to the surface of the silicide film. The temperature for the transformation of NiSi to NiSi 2 is relatively irrelevant to the presence of the Ti interlayer. A preferential orientation of ͑200͒ and ͑002͒ was found in the NiSi phase formed via the Ti interlayer, which significantly improved the epitaxial quality of NiSi 2 on Si͑100͒ substrate with a stepwise interface bounded by ͑111͒ and ͑100͒ planes. The top continuous Ti-related layer causes the incomplete accommodation of the thermal stress for the system. Upon disintegration of the Ti-related layer, the thermal stress of the system could be completely accommodated by relaxation of the NiSi layer.Metal silicides have been widely used in ultralarge scale integrated ͑ULSI͒ circuits to reduce the contact resistance of source/ drain in complementary metal-oxide-semiconductor ͑CMOS͒ devicess. Currently, the most commonly used silicides are TiSi 2 and CoSi 2 . For TiSi 2 , the transformation from the high-resistivity C49-TiSi 2 phase to the low-resistivity C54-TiSi 2 phase is nucleation limited, 1-3 causing linewidth dependence of the sheet resistance for gate lines narrower than submicrometer dimension. Therefore, CoSi 2 and NiSi have emerged as the most promising candidates to replace C54-TiSi 2 in self-aligned silicide ͑salicide͒ technology. However, as the lateral dimension continues to shrink, the junction depth of the device also decreases. The requirement of the shallow junction makes the silicon consumption by the silicidation process an important issue. For 0.1 m technology, even CoSi 2 is not a satisfactory material. Hence, NiSi is being investigated as a candidate for future device technologies because the same sheet resistance can be obtained with less Si consumption compared to CoSi 2 . 4 NiSi is not the final stable phase for the Ni/Si reaction system. Once the processing temperature goes higher than 800°C, NiSi transforms into NiSi 2 phase. Realization of the ULSI application for NiSi demands that the thermal stability of the phase be extended as much as possible. 4-7 Recently, great efforts have been made to study the thermal stability of NiSi, reportedly being improved by use of a thin Pt, [8][9][10][11][12][13][14][15]16 and Co 16 interlayer between the Ni film and Si substrate. The sheet resistance of the reaction system remains at the same low level in a wide temperature range. In general, the exploration of different interlayers on a react...

Impact of an ultra-thin Ti interlayer on the formation of NiSiGe/SiGe

“…This layer may contain Ti, Ni, Si, Ge and O elements (noted as Ti-related layer). Similar results have been already reported in the Ni/Ti/Si systems [15]. Considering the Ge two peaks distribution in Fig.…”

Thermal stability of Ni(Pt) silicide films formed on poly-Si

“…After selective etching (to remove the unreacted metal), bubble formation was not observed as in the 350°C sample, indicating full consumption of metal layers. This temperature range is similar to that of Chiu et al [10] observed for c-Si, and larger than layer inversion starting at 550°C, observed by Nygren et al [7] for pure Ni on poly-Si. At temperatures above 700°C, an increase in the sheet resistance is observed mainly due to the start of silicide/poly-Si layer inversion and agglomeration.…”

“…High R s values above 10 X/sq. was again observed for the sample obtained at the silicidation temperature of 350°C, probably due to the uncompleted formation of the Ni(Pt)Si alloy [9,10]. Post-annealing treatments confirm this assumption as the sheet resistance diminishes to half of the initial value (Fig.…”

“…First, the metal is not completely consumed at 350°C, noticed by the strong reaction of this sample in the H 2 SO 4 solution. To fully convert 15 nm of Pt into PtSi at 300°C requires around 120 s [9], moreover, the transition of Ni 2 Si to NiSi occurs at about 350°C [10]. In the experimental conditions of this sample, Ni x Pt y Si could be formed (x and y > 1), with a high resistance of 22 X/sq.…”

Improvement of Thermal Stability of Nickel Silicide Using Co-sputtering of Ni and Ti for Nano-Scale CMOS Technology

“…Based on the results of XRD in Fig. 5, the majority of Ti atoms appear near the surface of the film and it can be assumed that Ti does not combine with Ni or Si to form a compound [10]. Moreover, there was a thin surface Ti-related layer (maybe Ti w Ni x Si y O z or a mixture of compounds containing these elements) above the NiSi layer.…”