Near term and future experiments in high-energy physics and molecular biology will require radiation hard and fast detectors with sensitive border to cope with the increasingly stringent research requirements. 3D detectors, with vertical electrodes penetrating through the entire silicon substrate have drawn high interests for these applications due to their unique advantages such as ultra-fast time response, edgeless capability and radiation hardness. In addition, the through-wafer electrode technology can provide the possibility to connect 3D detectors on a wafer level via 3D interconnects [1, 2]. Since its introduction by S. Parker and C. Kenney in 1995 , several laboratories have begun research on 3D processing technology. Besides their advantages, fabrication of 3D detectors remains non-trivial and has only been possible since the successful developments in wafer bonding and deep reactive ion etching (DRIE). The edgeless capability is achieved by etching a through-wafer trench that surrounds an entire detector, and is then filled with highly doped silicon to form an active edge electrode. The process wafer must be bonded to a support wafer prior to the etching. Moreover, following polysilicon deposition, the process wafer is subject to severe mechanical stress and risk of cracking, making the support wafer even more necessary. At SINTEF MiNaLab, the first prototype run started in 2007, with an emphasis to demonstrate the feasibility to fabricate full 3D detectors with active edge on a production scale. During this run, wafer bonding was used to facilitate the etching of trenches and to provide mechanical support to the process wafer. A deep reactive ion etching process was also developed to etch 14 µm round holes through 250 µm thick silicon wafer. The first run is now fully completed and preliminary results are promising. Good p-n junction characteristics have been shown, and a leakage current of less than 0.5 nA per pixel was measured on selected devices. SINTEF is now the second laboratory who has successfully fabricated 3D detectors with active edge and is the first who attempted to fabricate on a production scale. This paper discusses the processing issues encountered in this first prototype run, with a focus on two important processes; wafer bonding and deep reactive ion etching (DRIE).
Keywords: 3D detector, wafer bonding, deep reactive ion etching, 3D interconnect, silicon sensor