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For poly Si channel applications used in three-dimensional (3D) flash memory devices, amorphous Si films deposited on thin SiO2 on Si wafers were converted to poly Si by solid-phase crystallization in the temperature range of 600 ~ 1050oC under Ar, N2 and forming gas (N2 96% + H2 4%) ambients. Annealing temperature and process ambient gas dependence of the poly conversion process was studied. The degree of amorphous to poly conversion and grain size distribution of poly Si were investigated using Raman spectroscopy. Six different Raman excitation wavelengths, with different probing depths, were tested to observe the uniformity of amorphous to poly Si conversion in the depth direction. No significant excitation wavelength dependence of the Raman spectra was observed from the converted poly Si, implying fairy homogeneous conversion throughout the thickness of film.

Feasibility of multiwavelength Raman spectroscopy was studied as a potential in-line monitoring technique for grain size distribution in channel poly-Si used in three dimensional stacked NAND (3D NAND) Flash memory devices. Various channel poly-Si materials in 3D-NAND Flash memory devices, converted from chemical vapor deposition (CVD) grown a-Si, were characterized using non-contact, multiwavelength Raman spectroscopy and high resolution cross-sectional transmission electron microscopy (HRXTEM). The Raman characterization results were compared with HRXTEM images. The correlation between the grain size distribution characterized by multiwavelength Raman spectroscopy and “on current” (ION) of 3D NAND Flash memory devices was investigated. Good correlation between these techniques was seen. Multiwavelength Raman spectroscopy is very promising as a non-destructive in-line monitoring technique for grain size distribution in channel poly-Si used in 3D NAND Flash memory devices.