Abstract
3D detectors, with vertical electrodes penetrating through the entire silicon substrate have drawn high interests for future particle tracking and medical imaging applications due to their unique advantages such as ultra-fast time response, edgeless capability, low initial depletion voltage and radiation hardness. In addition, the through-wafer electrode technology can provide the possibility to connect 3D detectors via 3D interconnects on a wafer level. Since its introduction by S. Parker and Chris Kenney in 1997, several laboratories have started to develop 3D detector fabrication technologies. SINTEF MiNalab possesses state-of-the-art tools for deep reactive ion etching (DRIE) with the possibility of making high quality vertical electrodes. These tools have robot cassette to cassette operation, and when used together with other automated processing equipment offers the possibility of small and medium scale production. Thus in 2006, SINTEF joined the original 3D collaborators (S. Parker et.al) in an attempt to transfer the technology to a production scale, and the first prototype run of true 3D-devices with active edge was started in 2007. During this first run, many fabrication issues were encountered and the compatibility of 3D wafers with our existing fabrication tools was at times challenging. After solving the problems of adapting the DRIE tools to the 3D process, a serious problem was encountered when handling the wafers after the polysilicon deposition. In the true 3D process the through-wafer electrodes are formed by filling the DRIE etched holes and edge trenches with highly doped polysilicon. This process, however, creates mechanical stress and bow in the wafers, making them fragile and problematic to handle. Despite the fabricating issues, the first prototype run is now near its completion and preliminary results are promising. Good p-n junction characteristics has been shown on successfully completed ATLAS n-readout devices made on n-type wafer
