Abstract-Thermocompression bonding joins substrates via a bonding layer. In this paper, silicon substrates were bonded using gold thin films. Experimental data on the effects of bonding pressure (30 to 120 MPa), temperature (260 and 300 C), and time (2 to 90 min) on the bond toughness, measured using the four-point bend technique, are presented. In general, higher temperature and pressure lead to higher toughness bonds. Considerable variation in toughness was observed across specimens. Possible causes of the nonuniform bond quality were explored using finite element analysis. Simulation results showed that the mask layout contributed to the pressure nonuniformity applied across the wafer. Finally, some process guidelines for successful wafer-level bonding using gold thin films are presented.[1170]

Abstract-Thermocompression bonding of gold is a promising technique for achieving low temperature, wafer-level bonding. The fabrication process for wafer bonding at 300 C via compressing gold under 7 MPa of pressure is described in detail. One of the issues encountered in the process development was e-beam source spitting, which resulted in micrometer diameter sized Au on the surfaces, and made bonding difficult. The problem was solved by inserting a tungsten liner to the graphite crucible. Surface segregation of Si on the Au surface at the bonding temperature was observed. Using Auger spectroscopy, a 1500 Å SiO 2 barrier layer was shown to be sufficient in preventing Si from reaching the surface. Lastly, a four-point bend delamination technique was used to quantify the bond toughness. The associated process steps that were required to prepare the test specimens are described. The critical strain energy release rate for the bonds ranged between 22 to 67 J/m 2 and was not shown to be strongly associated with the gold bond layer thickness in the thickness range studied (0.23 to 1.4 m).[828]Index Terms-Thermocompression bonding, wafer bonding.

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Abstract-We have micromachined a mechanical sensor that uses interferometry to detect the differential and absolute deflections of two adjacent cantilevers. The overall geometry of the device allows simple fluidic delivery to each cantilever to immobilize molecules for biological and chemical detection. We show that differential sensing is 50 times less affected by ambient temperature changes than the absolute, thus enabling a more reliable differentiation between specific cantilever bending and background effects. We describe the fabrication process and show results related to the dynamic characterization of the device as a differential sensor. The root-mean-squared (rms) sensor noise in water and air is 1 nm over the frequency range of 0.4-40 Hz. We also find that in air, the deflection resolution is limited only by the cantilever's thermomechanical noise level of 0.008 A Hz 1 2 over the frequency range of 40-1000 Hz.[781]

We demonstrate a promising type of microfabricated accelerometer that is based on the optical interferometer. The interferometer consists of surface-micromachined interdigital fingers that are alternately attached to a proof mass and support substrate. Illuminating the fingers with coherent light generates a series of diffracted optical beams. Subangstrom displacements between the proof mass and frame are detected by measuring the intensity of a diffracted beam. The structure is fabricated with a two-mask silicon process and detected with a standard laser diode and photodetector. We estimate that the minimum detectable acceleration is six orders of magnitude below the acceleration of gravity, i.e., 2 μg/Hz in a 1 Hz bandwidth centered at 650 Hz.