Tuning the Dimension\nof Ge Confined Cavity on Dielectric\nLayer through\nControlled Exposure of Si Ring

Epitaxial lateral overgrowth (ELO) is a crucial technique\nin semiconductor\nfabrication, particularly for applications that require precise control\nover material properties and structure at the nano/microscale. For\nthe free-standing dielectric layer on the micrometer scale, the formation\nof cavities occurs during ELO as the lateral growth fronts encounter.\nIn this paper, we report that, by controlling the width of the exposed\nSi ring, the dimension of the formed cavities can be manipulated,\nwhich effectively avoids the vertical epi-growth on unwanted areas\nand thus is particularly beneficial for applications that require\na compact and integrated layout of cavities. To formulate a consistent\nmodel for lateral epitaxial and cavity formation, we adopt a phase-field\nmethod to simulate the epitaxial film growth of Ge on a SiO<sub>2</sub>-patterned Si substrate. Our dimensional analysis reveals that the\nfinal cavity size is governed by surface energy and scales with the\nSi ring size. The simulations further reveal that the inward ELO determines\nthe cavity size through surface diffusion, proven by varying surface\ndiffusion mobility. Additionally, we find that the curvature differences\nbetween the inner and outer rims of the Si-ring affect the preferential\ndirection of the ELO, thereby controlling the inward or outward growth.\nThe results reported here provide a simple but effective strategy\nfor the controllable fabrication of nanocavities, enhancing design\nflexibility for devices that require a tunable and compact cavity\nstructure.