Analyses for stoichiometry and for Hydrogen and Oxygen in silicon nitride films

Abstract

Optical, ion, and electron probe techniques can be effectively applied to analyze for H, O, and the Si/N ratio in thin films of silicon nitride. The films studied were formed by chemical-vapor deposition or plasma deposition for application as a gate dielectric in semiconductor memory devices and for circuit encapsulation. The H concentration is measured by the multiple internal reflection technique which detects NH and SiH vibrational modes. A decrease in SiH bonding with an increase in deposition temperature is shown for chemical-vapor-deposited silicon nitride, and a very high concentration of SiH bonds is observed in plasma-deposited silicon nitride. Ion back-scattering analysis is a direct method for measuring the Si/N ratio and a related nuclear reaction analysis technique is a direct method for measuring and profiling the O content. Backscattering analysis shows a significantly larger Si/N ratio for plasma than for chemical-vapor-deposited silicon nitride. The O profile obtained by reaction analysis for a nitride/oxide/Si structure is compared to that obtained by sputter Auger electron spectroscopy, and the results show that O concentrations down to ∼0.5 at % can be measured by either technique. Auger analysis gives better depth resolution than reaction analysis but it requires a calibration standard. Auger results also show N penetration of interfacial SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and accumulation of N at the Si-SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> interface.