SEQUENTIAL ION-BEAM SYNTHESIS OF BURIED SI3N4 LAYERS IN SILICON

Ion beam synthesis was performed by implantation of 150 keV N+ ions in to silicon. The redistribution of nitrogen implanted at a dose of 1.2 x 10(17) cm-2 Was studied by SIMS as a function of annealing temperatu re (850, 1000, 1100, or 1200-degrees-C). In case of sequential ion bea m synthesis the total implantation dose was 5.7, 7.6, and 9.5 x 10(17) cm-2. Three series of specimens were annealed upon each increase of t he implantation dose at temperatures of 850, 1100, and 1200-degrees-C. The final annealing was carried out for 2 h at 1200-degrees-C. Thus o btained specimens were studied by the XTEM technique. It has been esta blished that during annealing the implanted nitrogen atoms move to the region of the concentration profile maximum. Such nitrogen redistribu tion depends on the annealing temperature in a nonmonotonical way. At annealing temperatures of 1000 and 1100-degrees-C an intermediate peak of nitrogen concentration is formed in the Si layer. In the sequentia l synthesis, the buried Si3N4 layer shows a porous region at implantat ion doses of 7.6 and 9.5 x 10(17) cm-2. The highest degree of structur al perfection in the buried Si3N4 layer and the upper Si layer was obs erved for specimens obtained upon intermediate annealing at 1100-degre es-C.