Effect of Pt addition on growth stress and thermal stress of NiSi films

Abstract

We have studied the effect of the addition of Pt on the growth stress and thermal stress of NiSi films. Platinum was added in the form of an interlayer (Ni/Pt/Si), capping layer (Pt/Ni/Si), and as an alloying element within the as-deposited Ni film (Ni–Pt/Si). The evolution of film stress during the solid-state reaction was monitored using in situ curvature measurements. The large transient compressive growth stress observed during the reaction of pure Ni with Si was significantly reduced for samples with a Pt interlayer or alloy. Based on in situ XRD measurements, this reduction in the compressive growth stress could be related to the disappearance of Ni rich phases from the phase sequence and an overall increase in the silicidation temperature during ramp anneals. Pt was also found to affect the buildup of thermal stress while cooling down the sample after Ni1−xPtxSi formation. The presence of Pt as a solute in the monosilicide causes a significant increase in the stress relaxation temperature, and therefore, in the total thermal stress as observed at room temperature. For a Pt interlayer, we observed a faster buildup of thermal stress, which could be related to a preferred epitaxial orientation of the monosilicide grains in this film as revealed by pole figure measurements.