Radiation Effects on Standard and Oxygenated Silicon Diodes D. Bisello, Member, IEEE, A. Candelori, Student Member, IEEE, A. Kaminski, D. Pantano, R. Rando, J. Wyss, A. Andrighetto, and V. Cindro Abstract--Silicon diodes processed on standard and oxygenated silicon substrates by two different manufacturers have been irradiated by neutrons in a nuclear reactor and by the 9 Be(d,n) 10 B nuclear reaction. The leakage current density (J D ) increase is linear with the neutron fluence. J D and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. On the other hand, standard devices from one manufacturer present the lowest acceptor introduction rate (β) for the effective substrate doping concentration (N eff ) suggesting that the β dependence on the particular process can be important for devices irradiated by neutrons, overtaking the small substrate oxygenation effect. Finally the average saturation value of the N eff reverse annealing is slightly lower for the oxygenated samples, pointing out the positive effect of the substrate oxygenation. I. INTRODUCTION I N the High Energy Physics experiments of the Large Hadron Collider at CERN (Geneve, Switzerland) the pixel and microstrip silicon detectors will be exposed to high hadron (protons, pions and neutrons) fluxes. Fluences up to 1.6×10 14 1-MeV equivalent neutrons/cm 2 will be delivered in the 10 year CMS experiment lifetime [1]. The damage induced by hadrons in the detector bulk causes: 1) an increase of the detector leakage current (J D ) [2]- [11]; 2) an increase of the detector depletion voltage (V dep ) if devices are irradiated beyond space charge sign inversion (SCSI) [3]-[17]. Moreover after irradiation and the short time (≈10-20 days) beneficial annealing, V dep starts again to increase due to the reverse annealing effect [3]- [6],[12],[15],[17], which at room temperature continues for many years. The V dep increase is consequently a huge problem taking into account that: 1) detectors have to operate in over-depletion to maximize the charge collection; 2) high bias voltages (>500 V) can lead the detector to junction breakdown. This work was supported by Istituto Nazionale di Fisica Nucleare and RD48 (ROSE: Research and Development on Silicon for future Experiments) collaboration. D. Bisello, A. Candelori, A. Kaminski, D. Pantano, R. Rando and A. Andrighetto are with Istituto Nazionale di Fisica Nucleare and Dipartimento di Fisica, Università di Padova, via Marzolo 8, I-35131, Padova, Italy (telephone: +39-049-8277215, e-mail: surname@pd.infn.it). J. Wyss is with Facoltà di Ingegneria, Università di Cassino, via DiBiasio 43, I-03043, Cassino (FR), Italy (telephone: +39-0776-299612, e-mail: wyss@pd.infn.it) and Istituto Nazionale di Fisica Nucleare, via Livornese 1291, I-56010, S.Piero a Grado, Pisa, Italy. V. Cindro is with Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia (telephone: +386-1-4773726, e-mail: vladimir.cindro@ijs.si). The RD48 (ROSE) collaboration at CERN [18],[19] has widely investigated how the V dep increase can be mitigated by substrate oxygenation, i.e. by introduction of high oxygen concentrations ([O]>10 17 cm -3 ) in the silicon bulk of devices exposed to charged hadrons (protons and pions) [6]- [11],[13],[14],[16]-[19]. Oxygen reacts with radiation induced vacancies (V), preventing the formation of the electrically active V-V defects which contribute to the V dep increase and to the reverse annealing. Measurements performed after 24 GeV proton irradiation [6] show that the increase of V dep depends in a sizeable way by the production characteristics for diodes on standard silicon, whereas the behavior of oxygenated diodes is independent of the production process and appears as a low bond for the V dep increase rate. The oxygen mitigating effect is reduced when radiation induced defects are produced in great number in limited regions (clusters), where the defect density is orders of magnitude higher than the highest achievable oxygen concentration [16],[17]. This happens not only by substantially decreasing the charged hadron energy but also when devices are irradiated by neutrons, because the Coulomb scattering is now absent and the cluster generation dominates: this phenomenon has been experimentally verified by nuclear reactor neutrons [5],[6], which well mimic the energy spectrum of the evaporation neutrons expected in the LHC experiments. In previous studies [8]-[11] we reported on the V dep increase rate for oxygenated and standard (not oxygenated) devices after irradiation by 16 MeV, 27 MeV and 24 GeV protons: substrate oxygenation mitigates the V dep increase rate, which nevertheless presents a wide range of values if standard and oxygenated devices processed by different manufacturers are considered. This suggests that not only the oxygen concentration but also processing affects the diode radiation hardness after proton irradiations. In this contribution we extend our previous studies: diodes from two of the previous manufacturers (coming from the same production batches which were irradiated by protons) have been irradiated by two different neutron sources (nuclear reactor and 9 Be(d,n) 10 B nuclear reaction). After describing the devices and irradiation conditions in Section II, we will 189 0-7803-7324-3/02/$17.00 © 2002 IEEE