| This work focuses on technology for electrical through-wafer interconnects (ETWI), cantilever arrays, and the integration of these two devices. Micromachined cantilevers are very sensitive and versatile sensors, with important applications in surface science, lithography, data storage, and biochemistry. To apply the capabilities of cantilevers over larger areas and with higher throughput, it is important to develop arrays. ETWI aid the fabrication of arrays of released sensors, such as cantilevers, because they address geometrical issues in alignment, electrical wiring, and density. ETWI also have broad applications for integrated circuits and micromachined sensors and actuators, as they permit three-dimensional design flexibility and facilitate system integration through wafer stacking.; Recent industry improvements of deep silicon etching techniques, based on a time multiplexed inductively coupled plasma (TMICP) etch process, now allow significantly increased aspect ratios (greater than 20:1) and depths (hundreds of microns). This technology is experimentally characterized and applied to silicon through-wafer applications. The problems of accurately releasing silicon sensors and forming ETWI are addressed and used to fabricate a novel two-dimensional array of sensors with backside electrical connections. The array consists of individually addressable piezoresistive cantilevers with high-aspect ratio tips. TMICP plasma etching is used to fabricate 30 μm diameter ETWI using tungsten and passive isolation, producing an unfilled via interconnect with approximately 1 Ω resistance. Mechanical and electrical characterization of the sensors is presented, as well as array operation as a microscope.; To simplify process integration, improved ETWI are developed using a filled via of doped polysilicon. This interconnect is a passively isolated electrical through-wafer polysilicon plug, with a 20 μm diameter, 10–14 Ω resistance, and less than 1 pF capacitance. TMICP plasma etching from both sides of the wafer is used to achieve an extremely high-aspect ratio etch (20:1 through 400 μm). The process is compatible with standard lithography, standard wafer handling, and high-temperature processing. N-type and p-type versions are demonstrated, and isolated ground planes are added to provide shielding against substrate noise. Electrical properties of these ETWI are measured and analytically modeled. These ETWI are currently being integrated with two types of ultrasound transducer arrays. |
