AbstractThe nature of stable radicals in FP9120 positive photoresist films implanted with boron and phosphorus ions and deposited on the surface of single-crystal silicon wafers has been determined using the EPR technique. At an implantation fluence of 6 × 1015 cm−2, a narrow singlet isotropic line with a g-factor of 2.0064 is observed in the EPR spectrum. As the fluence increased to 1.2 × 1016 cm−2, the g-factor decreased to values close to the g-factor of the free electron. The concentration of paramagnetic centers was higher during implantation of phosphorus ions than in the samples implanted with boron ions. This difference is due to a smaller contribution of nuclear stopping during B+ implantation, which does not exceed 10–15% of electronic stopping. The formation of long-lived paramagnetic centers recorded by EPR a week after implantation of positive phenol–formaldehyde photoresist is due to the presence of a powerful system of conjugated >C=O and –C=C– multiple bonds in the structure of the radicals.