3D silicon sensors - Large area production, QA and development for the CERN ATLAS experiment pixel sensor upgrade

3D silicon sensors, where electrodes penetrate fully or partially through the silicon substrate, have been successfully fabricated in different processing facilities in Europe and the USA. They key to 3D fabrication is the use of plasma micromachining to etch narrow deep vertical openings which allow dopants to be diffused in and form the electrodes of the p-i-n junctions. Similar openings can be used at the sensor's edge to reduce the perimeter's dead area to be as narrow as 4 μm. Since 2009, four fabrication facilities of the 3D ATLAS R&D Collaboration started a joint effort aimed at one common design and compatible processing strategy for the production of 3D sensors for the LHC Upgrade and in particular for the ATLAS pixel Insertable B-Layer (IBL). In this project where the installation is aimed for 2013, a new layer will be inserted as close as 3.4 cm from the proton beams inside the existing pixel layers of the ATLAS experiment. The detector proximity to the interaction point will therefore require new radiation hard technologies for both sensors and front-end electronics. The latter, called FE-I4 is processed at IBM and is the biggest front end of its kind, with a surface area of about 4 cm
²
. This paper will discuss some design aspects, and the different approaches taken by the facilities. Results from both the qualification runs and the current production runs for the IBL are also reported.