In this paper, we discuss the use of low frequency (up to 300 MHz) radio waves (RF) to detect and characterize electrical defects present in the dielectrics of emerging integrated circuit devices. As an illustration, the technique is used to monitor the impact of thermal cycling on the RF signal characteristics (S-parameters, such as S11 and S21) of electrically active defects in three dimensional (3D) interconnects. The observed changes in the electrical characteristics of the interconnects were traced to changes in the chemistry of the isolation dielectric used in the through silicon via (TSV) construction; specifically to the conversion of chemical intermediates such as non-bridging silanol (Si-OH) to bridging siloxane (Si-O-Si). We suggest that these “chemical defects” inherent in the ‘as-manufactured’ products may be responsible for some of the unexplained early reliability failures observed in TSV enabled 3D devices. This low frequency RF technique could be optimized to complement, and in some cases compete favorably with, other thin film metrology techniques, such as ellipsometry and Fourier transform infrared spectroscopy (FTIR), for mass production environments.

The most common gas sensors are based on chemically induced changes in electrical resistivity and necessarily involve making imperfect electrical contacts to the sensing materials, which introduce errors into the measurements. We leverage thermal- and chemical-induced changes in microwave propagation characteristics (i.e., S-parameters) to compare ZnO and surface-anchored metal–organic-framework (HKUST-1 MOF) thin films as sensing materials for detecting ethanol vapor, a typical volatile organic compound (VOC), at low temperatures. We show that the microwave propagation technique can detect ethanol at relatively low temperatures (<100 °C), and afford new mechanistic insights that are inaccessible with the traditional dc-resistance-based measurements. In addition, the metrological technique avoids the inimical measurand distortions due to parasitic electrical effects inherent in the conductometric volatile organic compound detection.

Metal-oxide (MO) semiconductor gas sensors based on chemical resistivity necessarily involve making electrical contacts to the sensing materials. These contacts are imperfect and introduce errors into the measurements. In this paper, we demonstrate the feasibility of using contactless broadband dielectric spectroscopy (BDS)-based metrology in gas monitoring that avoids distortions in the reported resistivity values due to probe use, and parasitic errors (i.e. tool-measurand interactions). Specifically, we show how radio frequency propagation characteristics can be applied to study discrete processes on MO sensing material, such as zinc oxide (i.e. ZnO) surfaces, when exposed to a redox-active gas. Specifically, we have used BDS to investigate the initial oxidization of ZnO gas sensing material in air at temperatures below 200 • C, and to show that the technique affords new mechanistic insights that are inaccessible with the traditional resistance-based measurements.

Broadband dielectric spectroscopy (BDS) was used to study thin films of Ge2Sb2Se5 exposed to low fluence UV-irradiation that resulted in thermally reversible photo-induced changes (PICs) on the film surfaces. Changes were characterized by reversible changes in film morphology and changes in the microwave scattering signature prior to and following irradiation. The PIC resulting from irradiation formed a low modulus and electrically resistive layer at the film surface. Modest heating of the photo-exposed material to about 60 °C anneals out the photo-formed layer to leave behind a very thin layer of smooth, thermally stable material at the film surface. Re-exposure of the material to UV-light recreated a foamy layer, which anneals away with modest heating over several cycles. The broadband microwave insertion loss (S21) increased with the film morphology changes after UV light exposure and decreased with thermal anneal over several cycles. These changes are correlated with transformations in the film's surface morphology and possibly structural modifications in the amorphous film. Thus, the BDS analysis provided interesting new insights into the nature of photo-induced processes in chalcogenide films, such as the electrical resistance consequences of morphological/structural changes.