Effective testing for wafer reject minimization by terahertz analysis and sub-surface imaging

This paper outlines applications of terahertz spectrometry, terahertz reflectometry and sub-surface imaging for effective characterization of various aspects of semiconductor wafer testing. Exemplary results of scanning a wafer have been analyzed for defect determination. Additionally, terahertz reflectometry for controlling wafer polishing for planarization has been exemplified via high precision thickness monitoring. Application of terahertz spectrometry for identifying self-assembled monolayer (SAM) on a wafer is also outlined with example. The technique may be extended to other substrates transparent to terahertz radiation. Characterizing different SAM coated silicon wafers for identifying two different SAM species has been discussed. The Fourier transform absorbance spectra of both SAM specimens reveals several distinguishable absorbance peaks that may be used as signatures of the respective SAMs. The SAM having 18 carbon chain exhibits higher absorbance than that of the SAM comprised of 8 carbon chain. This is consistent with the higher molecular weight of the former.