An Active Pixel Sensor Fabricated Using 5mm Thick Si Wafer Material

Silicon-based sensors are used in most particle physics experiments. However, particle detectors that operate at high energies – roughly 30KeV to 3MeV – have requirements that cannot currently be met with silicon detectors. Instead, these detectors use large, cumbersome scintillators. To replace the scintillators with silicon detectors, the silicon mass would need a thickness ≥5mm. This thickness could be achieved by direct silicon bonding of the finished device wafer to a thick silicon sub-wafer. However, state-of-the-art direct wafer hydrophobic bonding technology needs a temperature higher than 600˚C to create reliable Si-Si chemical bonds; these extreme temperatures would damage the detector circuitry. To overcome this limitation, NHanced proposes to fabricate the detector directly on a thick silicon wafer. This can be achieved only by a flexible fabrication facility, as it requires non-standard tool tuning and equipment to accommodate the non-standard thickness. However, it is by far the most reliable way to build the detector, since the silicon substrate will be almost by definition a single crystal. Our fabrication facility has more than 20 years’ experience in fabricating and fast-delivering prototypes for a large variety of customers and applications. NHanced has demonstrated 3D integration of InP, GaAs, GaN, CMOS, and other materials. The fab has already processed wafers with a thickness twice that of standard wafers. In addition, NHanced has a longstanding partnership with Fermilab, for whom we are currently fabricating silicon sensors with high resistance substrates for use in high energy particle detector programs. All of these factors make NHanced a natural choice for this project. In Phase I, NHanced Semiconductors, Inc. will adapt the production lines at its wholly-owned foundry in North Carolina, and will demonstrate through simple test vehicles its ability to build circuitry on thick, non-standard silicon wafers. NHanced will test and analyze the wafers, create plans for process improvements, and build a commercialization support plan for low to moderate volume production. In addition, NHanced will work very closely with Fermilab to define a plan for designing a detector in preparation for the Phase II effort.