Location-Controlled Ge Grain Growth via Nanoscale Cooling-Hole-Assi-sted Laser Crystallization for Low-Thermal-Budget Monolithic 3D Integration

Abstract Monolithic three-dimensional (M3D) integration requires high-performance channel materials processed under strict thermal budgets (<400 °C). While germanium (Ge) is a promising candidate, the stochastic nature of grain boundaries (GBs) in conventionally crystallized films severely degrades carrier transport and device uniformity. In this work, we demonstrate a deterministic location-controlled grain (LCG) growth technique for Ge thin films utilizing a nanoscale “cooling hole” architecture combined with green nanosecond laser crystallization (GNSLC). Transient thermal simulations and microstructural analyses reveal that the nanoscale cooling holes act as localized thermal sinks, inducing lateral crystallization while maintaining the underlying substrate temperature below 240 °C. Furthermore, the incorporation of a silicon nitride (SiNx) capping layer modulates thermal dissipation and exerts stress-mediated growth, yielding highly ordered, single-crystal-like Ge domains up to 1.2 μm with GBs precisely confined between the nanoscale cooling holes. Back-end-of-line (BEOL)-compatible FinFETs fabricated within these deterministic grains exhibit superior electrical characteristics and significantly tightened performance distributions. Notably, the standard deviation of the subthreshold swing (SS) is reduced by more than 50% compared to conventional polycrystalline devices. By effectively eliminating random GB scattering from the active channel, this LCG platform significantly suppresses device-to-device variability. Ultimately, it provides a robust nanoscale material engineering solution for advanced heterogeneous M3D integration.