(a) Stress monitor is a four-resistor Wheatstone bridge composed of one piezoresistive resistor, shown schematically in white, fabricated along a ⟨110⟩ in-plane direction, and three nonpiezoresistive resistors, shown in black, fabricated along ⟨001⟩ in-plane directions; (b) temperature monitor consists of three nonpiezoresistors, shown schematically in black, fabricated along ⟨001⟩ in-plane directions that allows for a four-point resistance measurement. The cantilevers shown in both (a) and (b) are fabricated from -thick (110) Si wafers and are wide and long.
Schematic process flow of the MEMS processing used to create the Si microcantilevers. Once the top (110) Si wafer thickness is reduced to by grinding and CMP, the cantilevers are formed through backside and then frontside DRIE.
Tip deflection of a cantilever by a tungsten probe during piezoresistive response calibration. The image was obtained using a commercial optical interferometer system (Veeco WYKO) and provides vertical deflection data as a function of position along the cantilever.
Comb structure fabricated within the (110) device wafer to estimate the thickness of adjacent cantilevers. The step heights were measured using a profilometer (Tencor P10) over the scan length of . Since the thickness does not vary significantly over the length of the comb structure, the measurement provides a good estimation of the thickness of the adjacent cantilevers.
(a) Stress-thickness product vs film thickness measured during deposition of Cu at at room temperature. For comparison, the piezocantilever data are compared to a conventional laser reflectometry measurement performed in the same vacuum chamber; (b) measured temperature rise during deposition used to calculate the thermal stress correction.
(a) Stress-thickness product vs film thickness measured before and after a growth interrupt during deposition of Cu at at room temperature; (b) stress-thickness product vs time during the growth interrupt for a -thick Cu film.
Piezoresistive coefficient values for lightly doped Si (Refs. 21 and 22).
Values of for (100), (111), and (110) Si for various in-plane directions (Refs. 18 and 23).
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