Evolving IC technology influences impedance measurements
By Rick Nelson, Chief Editor -- Test & Measurement World, 11/1/2007
In semiconductor device and process characterization and model verification, wafer-level impedance measurements are a necessity, especially in a world of high-k, ultra-thin, and low-k dielectrics. In the Webcast “The A B C-V’s of Accurate Impedance Measurements on Wafer,” Andrej Rumiantsev, applications group manager at Suss MicroTec Test Systems, begins by summing up technology trends as described in the International Technology Roadmap for Semiconductors (ITRS): Integration levels are getting higher, devices are getting smaller, gate oxides are getting thinner, gate leakage is getting higher, and frequencies are getting higher. He then explains how those trends affect impedance measurements and how engineers can best ensure accurate, repeatable measurements.
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| On-wafer impedance measurement methods differ depending on the frequency of interest as well as on the type of instrumentation used. |
Rumiantsev describes the LCR meters and vector-network analyzers that can be used to make impedance measurements, and he describes in detail several methods for measuring impedance that differ based on the measurement frequency, the setup, and the equipment used (figure). He notes that LCR meters can be effective at relatively low frequencies (less than 3 GHz), while S-parameter extraction using a vector- network analyzer provides good repeatability and reliability to 110 GHz and beyond. He comments on the importance of environment control in any on-wafer impedance measurement, because DUTs are sensitive to temperature changes, electromagnetic interference (EMI), and light. To optimize measurement accuracy, he says, instruments should be integrated into a probe system to minimize cable lengths and eliminate feed-throughs.
The Webcast, sponsored by Suss and produced by Test & Measurement World and Semiconductor International, provides details on auto-balancing bridge (ABB), RF I-V, and S-parameter impedance-measurement methods. It also covers probe and probe-pad considerations as well as calibration and calibration-verification methods. You can view the archived Webcast at www.tmworld.com/webcasts.
