A Novel Method to Fabricate Multiple-layer SOI - Single-Crystal Si Nanomembrane Transfer and Stacking

摘要

Multiple-layer SOI, in which there are multiple device layers per unit area, is of great interest because it potentially enables fully 3D integration. It also offers the prospect of more complete integration between optics and microelectronics than is possible with purely 2D structures. Here we present a technique for transfer and stacking of multiple single crystal Si nanomembranes with intervening oxide layers, enabling fabrication of multiple-layer SOI. We explain how to overcome transfer challenges, the most important of which is unintentional bonding of nanomembranes to their host substrate during lift-off. We examine the surface roughness of the membranes using atomic force microscopy (AFM). Intriguingly, the intermediate spin-on-glass layers used in this work are rougher than the silicon layers above and below, indicating that membrane transfer can ameliorate roughness introduced by such layers. We have used this process to create multilayer Si/SiO_2 heterostructures, i.e., multiple-layer SOI. These structures naturally function as Bragg reflectors, and thus their optical reflectivity can be used as a measure of structure quality. The reflectivity of one, two, and three membrane structures has been measured, and reflectivity above 99% has been achieved for three-layer samples.