Combined synchrotron x-ray diffraction and wafer curvature measurements during Ni–Si reactive film formation

Abstract

Combined x-ray diffraction and wafer curvature measurements during annealing of Ni thin films (13 nm) deposited on Si (001) reveal distinct stages in stress development and silicide growth. Thanks to this unique experimental setup, a clear correlation is established between force extrema at distinct temperatures and the appearance of new silicides. It is shown that the transient formation of Ni3Si2 has a strong influence on the overall stress development.

Exploring Ni–Si thin-film reactions by means of simultaneous synchrotron X-Ray diffraction and substrate curvature measurements

“…This curve is very similar to those obtained by Tsai [11], Liew [13] or Steegen [18]. The force evolution has been already described in five main stages [19,20] In this experiment, X-ray diffraction spectra are recorded at the same time. It allows for a very clear identification of different phases present at each stage.…”

“…This could be explained partly by the Ni 2 Si compressive stress relaxation, but the force becomes clearly positive at 230 • C, at variance with a simple stress relaxation. An explanation of this behavior may be found in the origin of the stress in the Ni 3 Si 2 layer as discussed in [19,20]. Briefly, the motion of one Ni atom results in two nearly simultaneous reactions a) at the interface Ni 2 Si/Ni 3 Si 2 : one Ni atom is released from Ni 2 Si resulting in Ni 3 Si 2 formation, which causes a 22% volume decrease in the Ni 3 Si 2 layer; (b) at the Ni 3 Si 2 /Si interface: following the previous reaction, the released Ni atom diffuses into Ni 3 Si 2 to form Ni 3 Si 2 , via Ni-Si reaction, which causes a 30% volume increase at the Ni 3 Si 2 /Si interface.…”

“…One should, however, note that a bell shape behavior may be obtained from a change in the sign of the growth stress. We effectively showed ( [19,20] and this work) for the Ni 3 Si 2 phase that the growth stress may change from compressive to tensile after complete Ni consumption and thus depends on the growth kinetics of each phase. Nevertheless, we did not explain why the strain does not increase continuously with the Ni 2 Si growth, or why the strain variation of Ni 3 Si 2 changes its sign when this phase is transformed into NiSi.…”

“…This means that the Ni 2 Si layer grows (i) under a high compressive stress and (ii) this compressive stress increases until complete Ni consumption. Beyond 215 • C, the stress decreases and is relaxed at 260 • C. The compressive stress buildup is probably related to the huge 62% volume expansion occurring during the transformation of one Si atom into one Ni 2 Si molecule [19,20]. B.…”

Kinetics of silicide formation over a wide range of heating rates spanning six orders of magnitude

“…For instance, NiSi formation starting from 13 nm Ni on single-crystalline Si is preceded by a mixture of Ni 2 Si and Ni 3 Si 2 phases. 5 In the present study, we focus our analysis on the reaction between Pd and Si, since only one stable phase forms below 800 C. [6][7][8] Overall mechanisms of silicide formation: diffusion plus reaction, and their activation energies are relatively well described in isothermal annealings or moderate temperature up scans for a variety of silicides. However, the dependence on ramp rate is not at the same level of maturity and further investigations are required.…”