Epitaxial growth of highly stacked SiGe(:B)/Si multilayers without strain relaxation for vertically stacked device applications

Abstract

The increasing demand for vertically stacked semiconductor devices has necessitated the fabrication of highly stacked epitaxial multilayers of SiGe/Si without crystalline defects. We propose a scheme that incorporates boron atoms into SiGe layers, yielding SiGe/Si multilayers with misfit-dislocation-free structures and no strain relaxation. The boron atoms are introduced in situ using ultra-high vacuum chemical vapor deposition, obtaining epitaxial multilayers consisting of boron-doped SiGe layers and undoped Si layers. The microstructures and strain states of the multilayers are observed using X-ray diffractometry, atomic force microscopy, and transmission electron microscopy. The relaxation thresholds increased with increasing incorporation of boron in both the single layers and multilayers. Incorporation of 0.6 % boron into the Si_0.8Ge_0.2 layers realizes a fully strained 110-period multilayer with a total thickness of 10.6 μm. Based on the kinetically limited critical thickness derived from the single-layer results, we successfully interpret the observed metastability limit in multilayer structures. This physical interpretation explains the substantially higher metastability of boron-doped SiGe/Si multilayers than of their undoped counterparts. This study demonstrates that boron-doping approach clearly enhances the strain retention in high-period multilayers, highlighting its potential in vertically stacked device applications.