Analytics and metrology of strained silicon structures by raman and nano-raman spectroscopy

Abstract

Straining the active regions in MOSFET devices is one of the key contributors to increase device performance in present and future technology nodes. Since dedicated strain on the transistor level is required with opposite sign for NMOS and PMOS transistors, the need to measure strain locally has become a challenge for analytics and metrology. Raman spectroscopy is capable of obtaining strain information non-destructively on the sub-μm scale, and therefore, this technique has been considered for process monitoring. In this paper it will be shown for silicon-germanium thin films, how both strain and composition can be determined independently by measuring two phonon modes of the film. This technique enables fast measurement of mechanical strain and chemical composition with high accuracy on the μm-scale. Thus, the micro-Raman technique is well suited for metrology of strained silicon test structures. Furthermore, it is shown that mechanical strain close to silicon-germanium structures can be measured with near-field resolution utilizing tip-enhanced Raman scattering (TERS). For device characterization, first steps of Raman-based approaches towards nano-Raman strain measurement in transistor channels have been done. However further development of this technique for improved deep submicron spatial resolution and for metrology applications is required. © 2007 American Institute of Physics.