Studying signal collection in the punch-through protection area of a silicon micro-strip sensor using a micro-focused X-ray beam

For the Phase-II Upgrade of the ATLAS detector (The ATLAS Collaboration, 2008 [1]), a new, all-silicon tracker will be constructed in order to cope with the increased track density and radiation level of the High-Luminosity Large Hadron Collider. While silicon strip sensors are designed to minimise the fraction of dead material and maximise the active area of a sensor, concessions must be made to the requirements of operating a sensor in a particle physics detector. Sensor geometry features like the punch-through protection deviate from the standard sensor architecture and thereby affect the charge collection in that area. In order to study the signal collection of n(+)-p(-)-p(+) silicon strip sensors over their punch-through-protection area, ATLAS silicon strip sensors were scanned with a micro-focused X-ray beam at the Diamond Light Source. Due to the highly focused X-ray beam (2 x 3 mu m(2)) and the short average path length of an electron after interaction with an X-ray photon (<= 2 mu m), local signal collection in different sensor areas can be studied with high resolution. This study presents results of high resolution 2D-scans of the punch-through protection region of ATLAS silicon micro-strip sensors, showing how far the strip signal collection area extends towards the bias ring and how the region is affected by radiation damage.