TVS Measurements of Metal Ions in Low-k Dielectrics: Effect of H 2 O Uptake
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1079-N05-08
TVS Measurements of Metal Ions in Low-k Dielectrics: Effect of H2O Uptake Ivan Ciofi, Zsolt Tökei, Giovanni Mangraviti, and Gerald Beyer IMEC, Kapeldreef 75, Leuven, B-3001, Belgium ABSTRACT Triangular Voltage Sweep (TVS) and Capacitance-Voltage (CV) measurements are gaining popularity in Back-End-Of-Line (BEOL) as techniques for studying drift of metal ions in low-k dielectrics. Recently, many works have been published on the topic. Although the experimental results that were presented are similar, the interpretations that were given are controversial. In order to gain better insight, we systematically investigated Metal-Insulator-Silicon (MIS) planar capacitors with different gate materials: Al, Cu, Ti, Ta, Ru and Pt, used as a reference. The insulator was an SiOC:H low-k film with 7% porosity and k value of 3.0. Besides, we also fabricated planar capacitors with amorphous silicon (a-Si) gate, which represents the case of metal-free capacitors. TVS and CV measurements were performed on the samples and the results we obtained for the different gate materials were very similar, including Pt and a-Si. We conclude that under low stress condition (190°C, 1MV/cm) neither of the quoted metals, except Cu, can drift into low-k materials. The TVS peaks and CV shifts observed on MIS capacitors are related to H2O uptake in low-k materials and are probably due to protons, generated during the measurement itself by electrical decomposition of H2O in the low-k film. INTRODUCTION In order to meet the strict performance requirements for next generation interconnects, different solutions are being considered for reducing interconnect RC delay without compromising reliability. New dielectrics with increased porosity and different metal barriers with higher conductivity are investigated to further reduce line-to-line capacitance and resistance of Cu/low-k interconnects. Considering the huge effort that is required to optimize an integration scheme for a new technology generation, it is important to identify possible issues with new materials in an early phase of development. In this respect, MIS capacitors are very suitable as a test vehicle. They allow fast electrical characterizations of dielectric films and metal barriers that are chosen as insulator and top electrode (gate) of the capacitor structure. The dielectric constant is derived from the MIS capacitance with the Si substrate in accumulation, which can be obtained through high frequency CV measurements. Dielectric contamination by metal ions injected from the metal gate under BTS is evaluated from the induced CV shifts. MIS capacitors are also suitable to evaluate the effect on low-k films of aggressive integration steps, such as plasma etch and strip. An interesting alternative to CV measurements for characterizing MIS structures is TVS measurements. They are basically current-voltage measurements, obtained by applying a triangular voltage sweep to the capacitor under investigation. TVS can be also regarded as a quasi-static CV and, as such, be used for capaci
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