Non-destructive Characterization of Nitrogen-implanted Silicon-on- insulator Structures by Spectroscopic Ellipsometry*

1. Introduction Silicon-on-insulator (SO1) structures implanted with 200 or 400 keV N ÷ ions at a dose of 7.5×1017cm 2 were studied by spectroscopic ellipsometry (SE). The SE measurements were carried out in the 300-700 nm wavelength (4.13-1.78 eV photon energy) range. The SE data were analysed by the conventional method of using appropriate optical models" and linear regression analysis. We applied a seven-layer model (a surface oxide layer, a thick silicon layer, upper two inter-]'ace layers, a thick nitride layer and lower two interface layers) with good results. The fitted parameters were the layer thicknesses and compositions. The results' were compared with data obtained from Rutherford backscattering spectros-copy (RBS) and transmission electron microscopy. The sensitivity of our optical model and fitting technique was good enough to distinguish between the silicon-rich transition layers near the upper and lower interfaces" of the nitride layer, which are unresolvable in RBS measurements. High dose implantation of reactive ions, such as oxygen, nitrogen or both, into silicon wafers has been successfully used to synthesize silicon-on-insulator (SOI) structures suitable for very-large-scale integration and radiation hard applications [1, 2]. The advantages of SOI devices have been noted by many investigators [3-5]. Parameters affecting the SOI microstructures have been extensively studied by Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) imaging, secondary ion mass spectrometry and Auger electron spectroscopy [6-10]. Quite recently, spectroscopic ellipso-metry (SE) has been used with success in the investigation of oxygen-implanted SOI [11, 12]. However, nitrogen-implanted SOI is more difficult , because of the stronger dependence of the microstructure on implantation dose. In this paper, we report the results of the characterization of SOI structures formed by a buried Si3N 4 layer. It is worth noting that the investigated samples are probably not the best for technological use. The emphasis in this paper is placed on the characterization method which may be the tool for future optimization experiments. In a previous paper [13], we applied multiple-angle-of-incidence (single-wavelength) ellipso