Nondestructive characterization of nanoscale subsurface features fabricated by selective etching of multilayered nanowire test structures using Mueller matrix spectroscopic ellipsometry based scatterometry

Nondestructive measurement of three-dimensional subsurface features remains one of the most difficult and unmet challenges faced during the fabrication of three-dimensional transistor architectures, especially nanosheet and nanowire based field effect transistors. The most critical fabrication step is the selective etching of silicon-germanium subsurface layers. The resulting shape and dimensions of the remaining Si(1-x)Gex structure strongly impacts further processing steps and ultimately the electrical performance of gate-all-around transistors, thus creating the need for accurate inline metrology. In order to demonstrate the ability to characterize this etch, nanowire test structures made from Si(1-x)Gex/Si/Si(1-x)Gex/Si/Si(1-x)Gex/Si multilayers have been characterized using Mueller matrix spectroscopic ellipsometry based scatterometry. Transmission electron microscopy images were used to corroborate the authors' scatterometry measurements. Here, they successfully demonstrate the ability to measure the Si(1-x)Gex etch, providing an industrially viable technique for inline three-dimensional metrology.