Manufacturing Process of Silicon Strip Sensors and Analysis of Detector Structures
Veröffentlicht am 01.08.2011 in
Due to their radiation hardness and fast performance with a good spatial resolution of several microns Silicon Strip Sensors became to the dominant technology for the inner tracker of sophisticated detector experiments. The inner tracker presents the heart of these experiments, as it is mounted close to the collision point of accelerated particles to track the trajectories of generated collision products. The main reason, which enables the success of this technology, can be found in the highly developed semiconductor technology. Due to the fact, that the manufacturing process of commonly used Silicon Strip Sensors is quite complex and expensive, large numbers can only be produced by commercial companies, which are usually specialized on other products.
In the course of the development of High Energy Physics higher energies and intensities are reached and better resolution became necessary, causing enhanced demands on sensors. Beside the constant reduction of material, for instance by double sided sensors or integrated pitch adapters - realized by a second metal layer - the demands on radiation hardness turned out to be problematic. Processes, which are necessary to produce these modified structures are not commonly used in semiconductor industry. Especially the problem of radiation hardness is actually irrelevant for commercial industry but nevertheless difficult to manage due to the strong influence of the material beside the structure design.
Consequently it seems necessary to involve scientific institutions as much as possible in the production process of Silicon Strip Sensors. Usually the institutes just deliver the design of the photo masks, arranging their sequence and perhaps give some special instructions concerning the function of structures and used material. But in fact the real process sequence remains unknown and hence the used material and mostly even the thickness of the different layers are unknown, too. The reasonable base of an expanded collaboration makes the knowledge of possible processes and enhanced analyzing tools necessary in order to understand their influence on detector performance.
Due to such problems the author developed a measuring station to determine doping profiles with "Spreading Resistance Profiling" and analyzed samples at the Scanning Electron Microscope. Both methods turned out to require special sample preparation, which has been developed in the course of the measurements. Moreover some test structures have been designed mainly to measure the contact resistance in order to ensure the functionality of special structures, expected to have improved radiation hardness. The mentioned tools have been applied on common structures and mostly on special structures and have been compared to established electrical measurements.
The results of the work are R&D motivated and are intended as a base for further investigations. Nevertheless concrete results have been achived, which have been mainly used as input parameter for simulations of the electrical fields inside the sensor bulk material. The main preparation and the work on the Scanning Electron Microscope has been performed at the technical university of Vienna in cooperation with the USTEM ("Universitäre Service-Einrichtung für Transmissions-Elektronenmikroskopie"). Data for simulations could be provided for the BELLE project to the "Institute of Particle and Nuclear Physics" at the Charles University Prague and for the CMS Project to the "Institut für experimentelle Kernphysik" at the Karlsruhe Institute for Technology (KIT).
Autoren: Wolfgang Treberspurg