High resolution electron microscopic and spectroscopic characterization of semi-insulating polycrystalline silicon and its interface with single-crystal silicon

Abstract

A combination of high resolution electron microscopy (HREM), electron energy loss spectroscopy (EELS), energy dispersive x-ray analysis (EDXA), and scanning transmission electron microscopy (STEM) techniques has been employed to characterize the structure and composition of vapor-deposited thin films of semi-insulating polycrystalline silicon (SIPOS) and their interfaces with Si. SIPOS layers containing ∼30 at. % of oxygen are amorphous when deposited at Si substrate temperature of 625 °C. Upon annealing at 900 °C in N2 for 30 min, Si crystallites up to ∼100 Å in size appear throughout the SIPOS layer, the microstructure of which appears to be a dispersion of Si crystallites in an amorphous matrix. The plasmon-loss spectra show a characteristic energy for each material: 16.7 eV for Si, 17.6 eV for SIPOS, and 23.2 eV for SiO2, which correlate empirically with increasing oxygen content in these materials. A combination of HREM and STEM revealed the existence of a 25–30-Å native oxide layer between the SIPOS and Si substrate. This native oxide yields a plasmon loss at 22 eV using a 10-Å probe in the STEM.