Study of vertical Si/SiO_2 interface using laser-assisted atom probe tomography and transmission electron microscopy

摘要

Laser-assisted atom probe tomography has opened the way to three-dimensional visualization of nanostructures. However, many questions related to the laser-matter interaction remain unresolved. We demonstrate that the interface reaction can be activated by laser-assisted field evaporation and affects the quantification of the interfacial composition. At a vertical interface between Si and SiO_2, a SiO_2 molecule tends to combine with a Si atom and evaporate as a SiO molecule, reducing the evaporation field. The features of the reaction depend on the direction of the laser illumination and the inner structure of tip. A high concentration of SiO is observed at a vertical interface between Si and SiO_2 when the Si column is positioned at the center of the tip, whereas no significant SiO is detected when the SiO_2 layer is at the center. The difference in the interfacial compositions of two samples was due to preferential evaporation of the Si layer. This was explained using transmission electron microscopy observations before and after atom probe experiments.