Steps towards the use of silicon drift detectors in heavy ion collisions at LHC

The inner tracking system of the ALICE detector for PbPb collisions at the LHC require a very good granularity in the innermost planes, due to the high particle density, up to 8000 particles per unit of rapidity. The silicon drift detectors are a very good candidate for this application, but up to now no large system using this technology has been industrially produced and operated in experiments. One of the first steps towards large scale production is the study of the doping uniformity in commercially available Si wafers. The understanding of doping fluctuations is of fundamental importance since they introduce deviations of the electron trajectories from the expected ones. In addition, it is also necessary to know the changes possibly introduced by different processing steps in the resistivity profiles. We report here the results of measurements of resistivity profiles for NTD silicon wafers both before and after processing.