Computer simulation of SIMOX and SIMNI formed by low-energy ion implantation

The computer program IRIS (Implantation of Reactive Ions into Silicon) has been modified and used to simulate low energy (< 100 keV), high dose oxygen and nitrogen implantation into silicon before and after annealing. There are some differences between high dose O ⁺ and N ⁺ implantation used to form buried insulating layers for SOI structures (SIMOX and SIMNI). Both ion species cause crystal swelling and surface sputtering and change the thickness of the layers. However the O/Si ratio in oxide layers saturates at the stoichiometric value of SiO ₂, whilst the N/Si ratio can exceed that of Si ₃N ₄. Nitrogen will accumulate in the silicon nitride layer, eventually being trapped as nitrogen bubbles. It is found that the method of sequential implantation and annealing will reduce the thickness of the top silicon layer in SIMOX samples, but has an opposite effect during nitrogen implantation.