Application of inline high resolution x-ray diffraction in monitoring Si/SiGe and conventional Si in SOI fin-shaped field effect transistor processes

Abstract

This study investigates the application of inline high resolution x-ray diffraction (HRXRD) for process control of Si/SiGe and conventional Si on silicon-on-insulator (SOI) fin-shaped field effect transistors (FinFETs). HRXRD measurements were taken from test pads on production wafers; the process stages under study were pre- and post-fin etch. For the pre-etch stage, HRXRD monitors the Si or Si/Ge thickness, Ge concentration (%), and crystal quality. For thickness, HRXRD results matched the fin height from a corresponding device within 2 Å. When equipped with a 1D detector, the typical measurement time can be as short as 20 min. In the post-etch stage, HRXRD monitors fin pitch with a precision of 3 nm. The choice of diffraction plane has an impact on the signal-to-noise ratio. In particular, the asymmetric 113 reciprocal space map (RSM) has better signal-to-noise than 004 for monitoring Si fins; however, pitch data obtained from these two diffraction planes matches within the measurement precision. The etch process can induce relaxation along the fin height in the Si/SiGe hetero-epitaxial fin and has a deleterious impact on the device’s drive current. Although the RSM is sensitive to such relaxation, a nanobeam diffraction measurement is still needed for quantitative strain measurements. The results show inline HRXRD is a valuable tool for monitoring pre- and post-etch processes during FinFET production. It can track vital fin parameters, including fin height, pitch, and crystal quality, which determine the final device drive current. The measurement is nondestructive and can be taken directly from testing pads in production wafers; it therefore saves testing cost and time and alleviates reliance on destructive techniques like transmission electron microscopy.