Raman Characterization of Poly-Si Channel Materials for 3D Flash Memory Device Applications

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 similar to 1050 degrees C under Ar, N-2 and forming gas (N-2 96% + H-2 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.