Near-Field Scanning Microwave Microscope for Interline Capacitance Characterization of Nanoelectronics Interconnect

We have developed a noncontact method for measurement of the interline capacitance in a Cu/low-k interconnect. It is based on a miniature test vehicle with net capacitance of a few femtofarads formed by two 20-mum-long parallel wires (lines) with widths and spacings the same as those of the interconnect wires of interest. Each line is connected to a small test pad. The vehicle impedance is measured at 4 GHz by a near-field microwave probe with 10- mum probe size via capacitive coupling of the probe to the vehicle's test pads. Full 3-D finite-element modeling at 4 GHz confirms that the microwave radiation is concentrated between the two wires forming the vehicle. An analytical lumped-element model and a short/open calibration approach have been proposed to extract the interline capacitance value from the measured data. We have validated the technique on several test vehicles made with copper and low- k dielectric on a 300-mm wafer. The vehicles interline spacing ranges from 0.09 to 1 mum and a copper linewidth is 0.15 mum. This is the first time a near-field scanning microwave microscope has been applied to measure the lumped-element impedance of a test vehicle.