Interface study of thermally driven chemical kinetics involved in Ti/Si3N4 based metal-substrate assembly by X-ray photoelectron spectroscopy

Abstract

Diffusion mediated interaction in metal-substrate assembly during high temperature annealing leads to possible formation of new composite materials. Here, sputtered grown Ti films on Si3N4/Si substrate has been reported to produce titanium nitride and silicide based binary composites while undergoing high vacuum annealing process at temperatures 650°C and above. Diffusion of thermally decomposed Si and N atoms from Si3N4 and their subsequent chemical reaction with Ti have been probed by X-ray photo electron spectroscopy. For annealing at 800°C and above, most of the Si atoms show preferences to stay in elemental form rather than developing silicide phase with Ti. Whereas at lower annealing temperature, silicide becomes the dominant phase for decomposed Si atoms. However, N atoms react promptly with Ti and form TiN which appears as the majority phase for each of the studied annealing temperature. Further, the nitride and silicide phases across the films have been compared quantitatively for various annealing temperature and the maximum silicide formation is observed for the sample annealed at 780°C. Finally, the thermally anchored metal-substrate interaction mechanism can be exploited to fabricate disordered superconducting TiN films where TiSi2 and Si can be used to tune the level of disorder by altering the annealing temperature.

A robust nitridation technique for fabrication of disordered superconducting TiN thin films featuring phase slip events

“…1 , 2 , we have demonstrated the variation of T c & R n with thickness & T a for disordered TiN thin films accompanied by nonsuperconducting minority phases of TiSi 2 and Si 18 . As T a plays a huge role in the decomposition of Si 3 N 4 and diffusion of Si & N elements inside the film 18 , the influential role of T a on particularly the superconducting properties of TiN thin films is also confirmed by the present study. It is noteworthy to mention that the achieved best T c by employing the current synthesis technique can be comparable, and some cases can be even better than, the reported conventional methods [Table S1 in the Supplementary Information (SI)].…”

“…As evident from Fig. 2 c at T a = 820 °C, a majority of the decomposed Si from Si 3 N 4 substrate remains as elemental Si which in turn contribute to the increased resistance in the normal state 18 . However, the change in R n with respect to thickness [Fig.…”

“…Here, R n reduces with decreasing T a from 820 to 750 °C and further reduction in T a leads to increased R n . Unlike T c , the dependence of R n on T a is not straightforward and that is mainly due to the presence of minority phases like TiSi 2 and Si that are generated and modulated by the annealing process 18 . Here, R n varies in the range between 60–87 Ω for T a ranging from 820 to 700 °C with its maximum value of about 87 Ω occuring at T a = 820 °C.…”

“…As the resistivity of TiSi 2 33 is lower than that of TiN 34 and of Si, the reduced R n for T a ≤ 780 °C compared to that of T a = 820 °C can be originated from the amount of TiSi 2 present in the composite film. Further, the relative concentration of minority TiSi 2 phase changes with T a 18 and hence, R n is expected to change with T a . As evident from Fig.…”

“…We demonstrate that by tuning the disorder the superconducting-to-normal state transition in the measured IVCs changes from a single step transition to a transition embedded with multiple steps featuring the formation of PSLs. The tuning of disorder level in TiN films has been achieved by adopting a novel substrate mediated nitridation technique 18 – 20 , which employs high temperature annealing of Ti/Si 3 N 4 based metal/substrate assembly to prepare majority phase TiN thin films accompanied by TiSi 2 and elemental Si as minority phases 18 . Conventionally, TiN films are grown either by using reactive dc sputtering of Ti in presence of Ar/N 2 gas mixtures 21 – 26 or by atomic layer deposition 27 , 28 in presence of N 2 gas etc 29 – 31 .…”