The concentration profiles of phosphorus and knock‐on nitrogen in silicon after phosphorous implantations into Si3N4‐Si systems have been investigated by using secondary ion mass spectrometry (SIMS). The tails were found on the phosphorus distribution in silicon after the implantation through Si3N4films. The concentration profiles of knock‐on nitrogen in silicon have been determined by measuring both the in‐depth profiles of knock‐on nitrogen and those of nitrogen after additional nitrogen implantation into a bare silicon embedded with knock‐on nitrogen. The concentration profiles of knock‐on nitrogen show a very high concentration near the surface and extending tails. It was found that the tails were observed at the deeper portion in silicon as energy increased, for a given Si3N4layer.