Improved SiPM device performance by introduction of a new manufacturing technology

Abstract

Silicon photomultipliers (SiPMs) are intensely evaluated as a potential replacement of photomultiplier vacuum tubes for several applications. Essential key features are the photon detection efficiency, the dark count rate, the optical crosstalk and the scalability of the active area and the microcell pitch. In order to achieve considerable improvements of these parameters, KETEK has introduced a new manufacturing technology based on 200 mm wafers and 0.35 μ stepper lithography. Important aspects of the well-established and for many years optimized KETEK Silicon Drift Detector technology could be transferred to the SiPM process. Main items of the new technology are a narrow vertical trench around the individual microcells and an impurity getter: the first reduces the optical cross talk and the second the dark count rate by factor two, whereby the potential of this technology is still not maxed out. A further aspect of the new technology is a low parasitic RC-value device concept: The reduction of parasitic RC-values is targeted on a scalability refinement of SiPM devices which is mandatory for active areas above 10 mm 2 . Finally the geometrical fill factor and the light entrance window of the KETEK device has been further improved for which reason a 50 μm cell pitch device with a photon detection efficiency of 60% in the blue range is presented. Beyond that the SiPM devices show an extremely low temperature coefficient of the gain. This is due to an operation at very high overvoltage along with a low temperature coefficient of the break down voltage.