LAUSR

Dear editor, Three-dimensional monolithic integration (3D-MI) has recently emerged for both “more Moore” and “more than Moore” applications, because of its high integration density, high bandwidth and multi-functions [1]. With 3D-MI, different types of devices can be stacked on the same platform and in a single process flow. A critical issue for 3D-MI is the formation of high-quality channels for the devices on the upper level under the constraints of low thermal budget and low cost. Several efforts have been reported to realize poly-Si thin film channels on SiO2 at low temperature, for example, laser annealing (LA) [2], solid phase crystallization (SPC) [3], and metal-induced lateral crystallization (MILC) [4]. LA can obtain a single-crystallike thin film, but needs extraordinary atomic-level chemical-mechanical polishing (CMP) to reduce surface roughness, which results in high process variation and cost. SPC is a common and simple technique, but its crystallization rate is too slow to efficiently form the active layer, and the random self-nucleation mechanism can lead to large fluctuations in grain size. MILC is another cost-effective method that can improve the crystallization rate, but suffers from serious metal contamination and a large number of dislocation defects in silicon grains because of metal-silicon inter-diffusion. In this study, a novel crystallization technique using low-temperature NiSi2-seed initiated lateral epitaxial crystallization (NiSi2-SILEC) is proposed. Using this technique, we perform an experimental demonstration, in which a 1-nm-thick Al2O3 layer is used to modify Ni diffusion and NiSi2 seed formation. The {111} facets of NiSi2 act as the initial seed window for silicon solidphase epitaxy. Additionally, a two-step annealing scheme is adopted to separate the two processes: NiSi2 formation and silicon epitaxial crystallization. Finally, the mechanism of NiSi2-SILEC is discussed in detail.