Schottky barrier structures have been formed by the deposition of Cu and Pt onn‐type Si(100) at room temperature. The structures were irradiated by 300 keV protons or 1.3 MeV alpha particles to doses between 109and 1010cm−2. Deep level transient spectroscopy measurements performed in the temperature range 80–290 K revealed a new level ∼0.31 eV below the conduction band edge in the proton‐bombarded Cu/Si(100) samples. The level exhibits metastable properties, and reversible cycling of its strength can be accomplished by a procedure where thermal annealing, forward biasing (hole injection), and white light excitation are undertaken. Evidence is presented showing that the level is associated with both Cu and H. Furthermore, the production rate of electrically active defects, e.g., divacancy and vacancy oxygen centers, is found to be substantially lower in the Cu/Si(100) samples compared with Pt/Si(100) samples irradiated under identical conditions. This is attributed to passivation of the irradiation‐induced acceptor centers by fast diffusing interstitial Cu+, and in particular, the effect is more pronounced at shallow depths close to the Cu/Si interface than in the deep tail beyond the implantation peak.