Silicon nitride layer in silicon formed by nitrogen implantation with multiple energy

The optimum dose for forming SOI structures suitable for devices by nitrogen implantation and subsequent annealing has been widely investigated for mono-energetic implantation. When nitrogen concentration is under the stoichiometric value of Si/sub 3/N/sub 4/, numerous small silicon islands are contained in the Si/sub 3/N/sub 4/ layer formed by annealing and cause a leakage current across the layer. When the concentration is above stoichiometry, nitrogen bubbles are formed and the layer becomes porous and fragile. By energy scanning or plural energy implantation, it is possible to keep the nitrogen concentration on the stoichiometric value over the wide range of depth. The optimum fluences for each energy in triple energy implantations (25 keV+50 keV+75 keV and 25 keV+50 keV+100 keV) were estimated by computer simulation using dynamic SASAMAL code. The implantations with these energies and fluences were performed. The nitrogen depth profiles were measured by NRA and compared with the calculated profiles. Surface topography was observed by AFM. The measured depth profile by NRA showed wide plateau of stoichiometric concentration of Si/sub 3/N/sub 4/ and the surface was very smooth even after high fluence implantation of 1.45/spl times/10/sup 18/ ions/cm/sup 2/ with the triple energy implantations.