Non-Equilibrium Growth of Surface Wrinkles Emerging in an SiO₂/Si Stack during Si Melting Induced by UV Nanosecond Pulsed Laser Annealing

Abstract

UV nanosecond pulsed laser annealing (UV-NLA) is demonstrating clear benefits in emerging 3D-integrated electronic devices, where the allowed thermal budget is strictly limited to preserve underlying device performance. A possible drawback of UV-NLA is that melting a solid substrate covered by a dielectric layer, which can be found in typical electronic device structures, induces wrinkles on the surface and may be an issue for subsequent processes. In this study, UV-NLA is performed in SiO2/Si structures to systematically investigate the emergence of wrinkles. A classical analytical model shows good agreement with our experimental results if a fitting coefficient is involved. Interestingly, its value rapidly increases for a thinner SiO2 film, whereas it becomes closer to unity for a thicker SiO2 film. This might infer a possible discrepancy of the material properties taken from literature and those of real industrial thin SiO2 films. The degree of the initial SiO2 film stress being negligible compared to the SiO2 shear modulus, its impact on the growth of wrinkles is not significant in our experiment.

Use of Nanosecond Laser Annealing for Thermally Stable Ni(GeSn) Alloys

“…Wrinkles appearance is related to a stress relaxation of the TiN capping layer, this layer having a compressive stress of about -6 GPa (We calculated the TiN film stress from wafer bow measurements before and after TiN deposition). When the GeSn underneath layer reaches the melting threshold, the stress of the TiN layer is released through deformation by wrinkles formation [44]. This unwanted phenomenon is relatively well known.…”