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 the 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 CMOS device structures, induces wrinkles on the surface and may be an issue for subsequent processes. In this study, UV-NLA is performed in thermally-grown SiO2/Si structures to systematically investigate the formation of wrinkles. A classical analytical model adopted from literature shows a good agreement with our experimental results if a fitting coefficient is involved. Interestingly, its value is rapidly increasing for a thinner (roughly less than 50 nm) SiO2 film, whereas it becomes closer to unity for a thicker (roughly greater than 50 nm) SiO2 film. This might infer a possible discrepancy of the material properties taken from literature and those of real industrial thin SiO2 films. The impact of the as-grown SiO2 film stress on the growth of wrinkles is also investigated, improving the statistics of the measurements. The results do not show any significant impact possibly because of the degree of the as-grown SiO2 film stress being negligible compared to the SiO2 shear modulus.