Spectroscopy: a new route towards critical-dimension metrology of the cavity etch of nanosheet transistors

Nanosheet Field-Effect Transistors (FETs) are candidates to replace today’s finFETs as they offer both an enhanced electrostatic control and a reduced footprint. The processing of these devices involves the selective lateral etching, also called cavity etch, of the SiGe layers of a vertical Si/SiGe superlattice, to isolate the future vertically stacked Si channels. In this work, we evaluate the capabilities of various conventional Critical Dimension (CD) and alternative spectroscopic techniques for this challenging measurement of a buried CD. We conclude that Raman and energy-dispersive X-ray spectroscopies are very promising techniques for fast inline cavity depth measurements.