Tuning the Dimension of Ge Confined Cavity on Dielectric Layer through Controlled Exposure of Si Ring

Abstract

Epitaxial lateral overgrowth (ELO) is a crucial technique in semiconductor fabrication, particularly for applications that require precise control over material properties and structure at the nano/microscale. For the free-standing dielectric layer on the micrometer scale, the formation of cavities occurs during ELO as the lateral growth fronts encounter. In this paper, we report that, by controlling the width of the exposed Si ring, the dimension of the formed cavities can be manipulated, which effectively avoids the vertical epi-growth on unwanted areas and thus is particularly beneficial for applications that require a compact and integrated layout of cavities. To formulate a consistent model for lateral epitaxial and cavity formation, we adopt a phase-field method to simulate the epitaxial film growth of Ge on a SiO₂-patterned Si substrate. Our dimensional analysis reveals that the final cavity size is governed by surface energy and scales with the Si ring size. The simulations further reveal that the inward ELO determines the cavity size through surface diffusion, proven by varying surface diffusion mobility. Additionally, we find that the curvature differences between the inner and outer rims of the Si-ring affect the preferential direction of the ELO, thereby controlling the inward or outward growth. The results reported here provide a simple but effective strategy for the controllable fabrication of nanocavities, enhancing design flexibility for devices that require a tunable and compact cavity structure.