Excimer laser-induced temperature field in melting and resolidification of silicon thin films

TLDR

The temperature response, melt propagation, and recrystallization evolution differ fundamentally between partial‑melting and complete‑melting regimes. In situ nanosecond electrical conductance, optical reflectance/transmittance, and thermal emission measurements of 50‑nm Si films on fused quartz reveal that latent‑heat balance keeps partial‑melting temperatures near the amorphous Si melting point, while complete melting permits >200 K supercooling and spontaneous nucleation. Recrystallized polycrystalline Si exhibits grain enhancement in the near‑complete‑melting regime, and its melting occurs near the crystalline Si melting point, roughly 140 K above the amorphous Si melting point.

Abstract

The liquid/solid interface motion and temperature history during excimer laser annealing of 50-nm-thick Si films on fused quartz substrates are investigated by in situ nanosecond time-resolved electrical conductance, optical reflectance, and transmittance at visible and near-IR wavelengths, combined with thermal emission measurements. The temperature response, melt propagation and evolution of the recrystallization process are fundamentally different in the partial-melting and the complete-melting regimes. Because it is necessary to balance the latent heat across the propagating phase-change interface, the maximum induced temperature in the partial-melting regime remains close to the melting point of amorphous Si. The peak temperature rises in the complete-melting regime, but the nonparticipating nature of the liquid Si/fused quartz interface allows substantial supercooling (>200 K), followed by spontaneous nucleation into fine-grained material. These phase transformations are consistent with the recrystallized polycrystalline Si morphologies that indicate grain enhancement in the near-complete-melting regime. It is also found that melting of polycrystalline Si occurs close to the melting point of crystalline Si. This temperature is by approximately 140 K higher than the melting point of amorphous Si.