Near-field scanning microwave microscope for interline capacitance characterization of nanoelectronics interconnect

TL;DR

This paper introduces a noncontact near-field microwave microscopy technique to measure interline capacitance in nanoelectronic interconnects, validated on test vehicles with femto-Farad sensitivity.

Contribution

It presents the first application of near-field scanning microwave microscopy for measuring the impedance of a test vehicle in nanoelectronics interconnects.

Findings

Validated measurement technique on copper/low-k test vehicles

Achieved femto-Farad sensitivity in interline capacitance measurement

Demonstrated applicability on 300 mm wafers with nanoscale features

Abstract

We have developed a noncontact method for measurement of the interline capacitance in Cu/low-k interconnect. It is based on a miniature test vehicle with net capacitance of a few femto-Farads formed by two 20-\mu m-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 \mu m probe size via capacitive coupling of the probe to the vehicle's test pads. Full 3D 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 \mu m and a copper line width is 0.15 \mu m. This is the first time a near-field scanning microwave microscope has been applied to measure the lumped element impedance of a test vehicle.