Prenucleation process for simox device fabrication

A method of producing a buried insulating layer in a silicon substrate comprising the steps of

• A. implanting a subcritical dose of at least one first ion species into said substrate to induce a controlled amount of damage to regions of the silicon lattice within a subsurface layer;
• B. creating nucleation sites in the damaged silicon lattice within said subsurface layer by heating the substrate following ion implantation to enlarge the damaged regions;
• C. implanting oxygen ions into said subsurface layer following the creation of the nucleation sites to deliver a total oxygen dose to the substrate less than 1.5.times.10.sup.18 ions/cm.sup.2 ;
• and
• D. annealing said substrate to form a buried layer of silicon dioxide in said silicon substrate.