Unveiling strain in future generation transistor technology by Bessel beam electron diffraction method

Abstract

Strain engineering is a common approach for enhancing the mobility of semiconductor materials and improving the performance of conventional and novel transistors. Understanding the strain distribution is important for optimizing device characteristics. Transmission electron microscopy (TEM) is a crucial technique for evaluating strain at the nanoscale. However, due to the ongoing reduction in electronic device dimensions, assessing strain via TEM has become increasingly challenging. Many different techniques have been developed in recent years with the aim of analysing complex structures. In this work, we investigate the capabilities of the recently developed Bessel beam electron diffraction (BBED) method to evaluate strain by TEM in fully processed fin-field effect transistor (FinFET) devices and in cutting edge nano-sheet complementary-FET (NS-CFET) technology. TEM analysis of fully processed devices is challenging due to the presence of artefacts generated by different materials and multiple structures overlapping in projection in TEM images. We demonstrate the capability of the BBED technique to reveal strain in fully processed FinFET while exploring the dependence of strain on layout variations. NS-CFETs are an attractive device architecture for beyond 1 nm logic technology nodes. Strain distribution in these devices is more complex than in FinFETs due to the presence of very thin layers and reduced channel dimensions. We compare the BBED method with the well-known techniques of nano-beam electron diffraction (NBED) and geometric phase analysis (GPA) for analysing strain in these structures. The BBED technique, despite a simple experimental setup, shows good accuracy and spatial resolution, being able to resolve interlayers thinner than 2 nm. Compared to NBED and GPA, the BBED technique offers better performance and is therefore a promising method to study strain in future transistor devices.