Anomalous carrier tail generation in BF+2ion‐implanted layers through gas‐ion interaction is quantitatively examined by a combination of gas pressure measurements and carrier profile measurements. The collision cross sections of He, Ar, Kr, and N2gases with BF+2ions are derived from the relative peak carrier concentrations of the tail and residual gas pressure relationships. Below 10−2Pa, simple gas‐ion interaction occurs and the collision cross section is around 10−14cm−2. A gas pressure of less than 10−5Pa in the implanter ion path is necessary to almost completely eliminate the anomalous tail generation. On the other hand, more than 4×10−1Pa, multiple collisions between the ions and the residual gas atoms/moleculs occur and the tail carrier concentration become saturated. BF3gas molecules are also foud to generate B+ions through collisions with BF+2ions.