Surface-near analyses of ultra thin silicon nitride layers by NRA, channeling RBS, FT IR ellipsometry and AFM

Abstract

Homogeneous ultra thin silicon nitride layers (SiN x layers) close to the surface have been produced by 10 keV 15 N 2 + molecular ion implantation and an ion current density of 10 μA/cm 2 , into single crystal silicon at room temperature. Stoichiometric SiN x layers with thicknesses of about 28 nm (analyzed by NRA) were obtained at fluences of 1.5 x 10 17 at/cm 2 . NRA anlayses of samples annealed by EB-RTA at T = 1150°C for 15 s indicated that the N/Si ratio and the layer thickness did not change drastically. FT IR ellipsometry analyses indicated the existence of Si 3 N 4 bonds in as-implanted specimens. A disordered Si layer (d-Si, typically 15 nm thick) underneath the implantation region caused by the ion implantation was found by channeling RBS analyses. The d-Si layer partly recrystallized during EB-RTA showing a thickness of 6 nm afterwards. The SiN x layers showed no decomposition and detachment after EB-RTA. Due to EB-RTA, however, the smooth surface of the as-implanted specimens changed into a surface with remaining whisker-like structures surrounded by circular recesses as shown by AFM analyses. A model for the growth of these whisker-liker structures caused by low energy ion implantation and EB-RTA is presented on the basis of the thickness of the SiN x layer, the existence of the d-Si layer and the special annealing process.