Nano-focused Raman spectroscopy for stress and compositional metrology

In advanced nanoelectronics transistor structures, strain can be used as a concept to enhance the mobility of electrons (or holes) in the channel region and thereby increasing the channel conductivity and overall device performance. At the same time, novel transistor channel materials such as compound III-V semiconductors are introduced in 3D integration schemes. Strain and composition measurements for process optimization on these structures generally require TEM-based techniques such as nano-beam diffraction (NBD) and convergent beam electron diffraction (CBED), or X-ray techniques like high-resolution X-ray diffraction (HRXRD). The main drawback of these approaches is that the measurement is destructive in nature and/or requires lengthy or large-scale integration using complex metrology tools. In this topic, the use and optimization of advanced micro-Raman spectroscopy is investigated for measuring the local stress and composition in next-generation semiconductor architectures. Specifically, nano-focused Raman, where a dramatic enhancement of the Raman response occurs under certain experimental conditions, will be employed for compositional and strain measurements in group IV and III-V finFETs, nanowires and multistacks. The focus of the topic will be on a detailed understanding of the active Raman modes in the materials of interest and their dependency on strain and composition in nanoscale semiconductors. Through cross-validation with other characterization tools from the imec metrology portfolio such as NBD and HRXRD, a non-destructive and quantitative metrology concept will be developed that is of paramount importance for future CMOS technology. Building on extensive in-house know-how, the PhD candidate will develop and optimize Raman measurement approaches and explore their interpretation for deep-subwavelength semiconductor structures, paving the way for re-enabled Raman stress and composition measurements at the nanoscale.