Utility of using power spectral density to characterize SOI layer thickness uniformity

The power spectral density (PSD) of silicon layer thickness uniformity of SOI wafers is a powerful metric for characterizing the quality of SOI materials and the methods used to achieve layer uniformity. This paper addresses the utility of using layer thickness PSD to analyze the common non-uniformities found in bonded SOI wafers and other SOI wafers. The PSD generalizes total rms thickness variation of a wafer to represent that part of an rms variation due to a specific range of spatial frequencies (i.e. the inverse of the spatial wavelength of the thickness variation). In addition, we describe how we apply the PSD and related information to improve the layer uniformity by means of confined plasma-assisted chemical etching (i.e. the AcuThin process)