Electron Microscopy investigations of buried Si3N4 isolation layers
Formation of buried Si3N4 layers obtained by using repeated cycles of implantation and annealing has been investigated. Structure investigations were made with the use of a CM30 Twin electron microscope (whose diaphragm is 0.18 nm-1 ). In HREM studies, axial micrographs in Si reflections of the 000, 111 and 220 types were employed. Two types of samples were used: "plane view" samples and those of a "cross section". Si3N4 precipitates were identified by application of the EELS method on the LN and Lsiedges.N+ - ions were implanted into silicon wafers (of p-type, (001), 10 Ω cm) at a room temperature- The dose pf ions implanted in each cycle was 5.1010 cm-2 . The total dose was 5.1017 cm-2 , The energy of ions - 150 keV, the current density of the ion beam 25 μA/cm-2 . Annealing in the atmosphere of nitrogen was made at 1100° C which lasted 2 hours after the first cycle of implantation; in the other cycles it lasted 0.5 hours at 850° C. After the operation of ion beam synthesis was completed a silicon epitaxial layer 0.8-1 μm thick was grown.