• Tuominen, Eija
• Vähänen, Sami
• Kalliopuska, Juha
• Tuovinen, Esa Veikko
• Arsenovich, Tatyana
• Härkönen, Jaakko
• Mäenpää, Teppo H.
• Luukka, Panja
• Kassamakov, Ivan Vladislavov
• Karadzhinova-Ferrer, Aneliya Georgieva
• Peltola, Timo

Abstract

A technical maintenance break of LHC running to deliver after 2015 the maximum possible amount of beam collisions for the experiments has started in early 2013. The CMS experiment will undergo its first major hardware upgrade, named as Phase I, during the shut-down period (LS1). The innermostmeasurement unit of the CMS, the silicon pixel detector will be completely rebuild and accompanied with new readout electronics and cooling system capable to handle essentially higher amount of data foreseen after LS1. The number of channels, i.e pixels and related interconnections, will simultaneously be increased from current 64 million up to 125 million channels allowing significantly better tracking performance. The CMS Upgrade project of Helsinki Institute of Physics (HIP) is involved in Phase I by production, including quality assurance (QA), of notable fraction of pixel sensor modules to be installed into<br/>upgraded detector. The on-going activity is carried out in cooperation with Finnish company Advacam Oy. The flip-chip interconnection processing is taking place at Aalto-VTT Micronova facility. A bare pixel module consists of a sensor and 16 read-out CMOS circuits (ROC) that are flip-chip (FC) bonded with the sensor. Alltogether the module has about 67 thousand pixels. Processing of the bare modules consists of several metal thin film depositions, lithograph steps, silicon wafer thinning, etching, electrochemical metal growth, silicon wafer dicing and it is carried out in the class 10 clean room premises of Micronova<br/>facilit. The acceptable level of bad interconnections in the module is less than 0.1%, thus the QA during the different process steps is crucial. First, characterization of the pixel sensors is done by current-voltage (IV) testing with a probe station. The second important QA step follows after the FC bonding of the 16 readout chips. The FC bonded pixel module will be tested with an automated probe station equipped with appropriate data acquisition (DAQ) hardware and software in order to reveal possible bad interconnections. In a case a malfunctioning readout chip is found, it is possible to liftoff an individual chip, and to replace it with a new one without sacrificing the whole 16- chip module.<br/>We have successfully produced first pre-series of the bare pixel modules. Module test measurements revealed less than ten bad interconnections out of more than 350 000 pixels and better than 98%yield of read-out ASICs.

Topics

• Deposition
• impedance spectroscopy
• phase
• experiment
• thin film
• laser emission spectroscopy
• Silicon
• etching
• hot isostatic pressing