The large-scale production of silicon sensors for the Phase-2 Upgrade of the CMS Outer Tracker

The high-luminosity upgrade of the Large Hadron Collider (LHC) at CERN will introduce a new period of challenges for the high-energy physics community. The increase of the peak instantaneous luminosity of the machine up to 5 $\times$ 10$^{34}$ cm $^{-2}$s$^{-1}$ (or 7 $\times$ 10$^{34}$ cm $^{-2}$s$^{-1}$ in the ultimate case) will provide with more statistics of the Higgs boson decays and expand the discovery potential especially for rare processes of the standard model or beyond standard model physics. The HL-LHC is expected to deliver an integrated luminosity of 3000 - 4000 fb$^{-1}$ by the end of its lifetime. The CMS (Compact Muon Solenoid) detector needs to undergo several upgrades in order to fully exploit the increase in luminosity delivered by HL-LHC. This upgrade program is known as the CMS \emph{Phase-2} upgrade. The innermost sub-detector of CMS, the tracking system (CMS Tracker), will be fully replaced with a more advanced detector which is designed to cope with the larger particle rates and the high radiation levels of HL-LHC. The Phase-2 Tracker consists of an Inner Tracker (IT) based on pixel sensors and an Outer Tracker (OT) based on strip and macro pixel sensors. The Outer Tracker requires about 26400 new silicon sensors. The production of the Outer Tracker sensors has started since the summer of 2020. This thesis describes the basic features of the new Outer Tracker silicon sensors and summarizes the CMS plan to monitor the stability and quality of large-scale production. This plan comprises the electrical characterization of the production sensors and the test structures on a sampled basis. The test structures are developed on the same wafers as the main sensors and they share the same properties. They provide quick access to several sensor parameters, many of which can not be directly measured on the main sensor, such as the flat-band voltage or they require potentially destructive tests, such as the breakdown voltage of coupling oxide. To date, the mass production of the Phase-2 Outer Tracker silicon sensors has exceeded 70$\%$ of the total. Hence, a sufficient number of data has been collected in order to characterize the production process. This thesis provides a summary of the evolution of all the measured sensor and wafer parameters over production time. A comparison and a correlation of all the parameters related to the same sensor properties is performed. An emphasis is given on those parameters which reveal trends and inconsistencies over production time. Apart from providing conclusions for the quality of the production sensors, this thesis attempts to prove the importance of process quality control as a tool to spot in-time fabrication process variations and to give a full insight into the wafer properties. Moreover, studies are conducted on the robustness of the Outer Tracker production sensors against external factors such as electrostatic charge-up and humidity. The electrostatic charge-up is an effect which concerns a large fraction of the Outer Tracker sensor production. The source of this effect, its impact on the electrical behavior of the production sensors as well as a mitigation strategy as defined by CMS, are presented in this thesis. Also, the impact of high relative humidity on the production sensors is investigated. The role of high relative humidity becomes more crucial during the module assembly stage due to the long exposure of the sensors to the humid environment of the ESD-safe clean rooms. The response of the sensors after a long exposure to humidity is examined and a recovery strategy is defined for those sensors which show a deterioration of their electrical behaviors due to humidity.