Characterization of silicon oxynitride thin films by x-ray photoelectron spectroscopy

There has been a considerable effort in the past decade to incorporate nitr ogen into SiO2 in order to improve the electrical properties of ultrathin ( 2-10 nm) gate oxides. Process conditions affect the nitrogen concentration, coordination, and depth distribution which, in turn, affect the electrical properties. X-ray photoelectron spectroscopy (XPS) is particularly well su ited to obtaining the nitrogen coordination and, to a lesser extent, the ni trogen concentration in thin oxynitride films. To date, at least four diffe rent nitrogen coordinations have been reported in the XPS literature, all h aving the general formula: N(-SixOyHz), where x + y + z = 3 and x less than or equal to 3, y less than or equal to 1, z less than or equal to 2. In th is article we review the XPS literature and report on a fifth nitrogen coor dination, (O)(2)=N-Si with a nitrogen Is binding energy of 402.8+/-0.1 eV. Next nearest neighbor oxygen atoms shifted the N(-Si)(3) peak roughly 0.1 e V per oxygen atom. We also discuss results from a , novel approach of deter mining the nitrogen areal density by XPS, the accuracy of which is dependen t on the depth distribution of nitrogen. Secondary ion mass spectrometry is used to determine the depth N distribution, while nuclear reaction analysi s is used to check the N concentration measured by XPS. (C) 1999 American V acuum Society. [S0734-2101(99)21904-5].