Measurements and Irradiations of Test Structures for the CMS Tracker Upgrade

Autoren: Bernhard Lutzer
Kategorie: Masters-Thesis

The silicon-strip tracker of the CMS experiment at CERN is currently (2012) in full operation. It delivers precise tracking information while it has to operate in a harsh radiation environment. This causes damage to the tracker which will lead eventually to a replacement of the whole detector after 10 years of lifetime. Additionally a further upgrade of the LHC accelerator is planned. This upgrade leads to a much higher luminosity which results in a much higher radiation background. Therefore new materials need to be found which are capable of tolerating higher radiation levels.


These requirements can only be achieved by research for the right materials. This is currently done within the so-called HPK campaign which is carried out by an institutional collaboration. Wafers are designed and produced by a industrial company within this campaign. These wafers differ by their production method (Floating Zone, Magnetic Czochralski, CVD), their doping and thickness. It is tried to determine the right material with different methods where one of those is done at our institute with so called test structures, TS.

These, containing different microelectronic structures like diodes, resistors, etc., were designed to be able to extract parameters which are not accessible in a silicon detector which are produced on the same wafer. Furthermore, these test structures will be irradiated with neutrons and protons for the purpose of simulating the particle fluence to assess the radiation damage inside the CMS tracker after 10 years of operation.


Measurements of both non-irradiated and irradiated test structures have been done for this thesis. Additionally, irradiations outside the campaign at the TRIGA Mark II reactor of the Institute of Atomic and Subatomic Physics in Vienna have been done by the author. The combined results of the work with other structures by other institutes this will lead eventually to a decision of the material.


The second topic of this work presents complementary measurement methods to get information about the quality of the oxide,the upper parts of the bulk and the interface between them by measuring the generation lifetime and surface generation velocity of the bulk on MOS capacitors. These parameters are regularly measured in the semiconductor industry. First results on non-irradiated test structures will be presented in this thesis.