Detection of Copper and Water in Low-k Dielectrics by Triangular Voltage Sweep Measurements
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0914-F02-02
Detection of Copper and Water in Low-k Dielectrics by Triangular Voltage Sweep Measurements Ivan Ciofi, Zsolt Tökei, Marco Saglimbeni, and Marleen Van Hove IMEC, Kapeldreef 75, Leuven, 3001, Belgium
ABSTRACT Metal-Insulator-Semiconductor (MIS) planar capacitors were fabricated in order to systematically investigate the effect of Cu and water in Cu/low-k structures by Triangular Voltage Sweep (TVS) measurements. We were able to resolve peculiar features in the TVS traces of Cu and water contaminated samples, which were related to Cu ions and protons, respectively. We demonstrate that these features can be used to distinguish the two ionic species. As a result, we provide a methodology that can be used to detect both Cu and water in low-k dielectrics embedded in MIS structures. Correlation with the CV method is also demonstrated. As an application, the methodology was applied to compare the effect of different plasma treatments on the performance of the same OSG material and an excellent correlation with Time Dependent Dielectric Breakdown (TDDB) data from the same samples was found. INTRODUCTION In the attempt to further reduce the interconnect RC delay, porous low-k dielectrics are being actively tested in combination with Cu for advanced interconnect schemes. It is known that the use of porous materials presents a number of process challenges. In particular, pores make the material prone to water absorption, which affects both performance and reliability of backend-of-line (BEOL) structures. Time Dependent Dielectric Breakdown (TDDB) tests are commonly used to predict the lifetime of interconnect schemes at user conditions: the time-tofailure is extrapolated from those obtained under different Bias Temperature Stress (BTS) conditions. However, the failure mechanisms associated with Cu and water are not yet fully understood. Besides, in TDDB tests it is often necessary to overstress the investigated structures in order to make them fail in a reasonable time. In this case the applied electric fields may be much higher than those expected at user conditions, which makes the validity of the related predictions questionable. In this work, we evaluated the TVS method [1] as a possible low electric field technique for addressing the degradation mechanisms that occur in Cu/low-k structures. The method consists in measuring the current produced by a slow linear voltage sweep applied to the MIS capacitor under investigation. When the applied voltage changes polarity, possible mobile ions in the dielectric, such as Cu ions, are revealed as a peak superimposed upon the capacitor’s displacement current and the related concentration is calculated from the area under the peak. Generally, BTS is performed before initiating the voltage sweep in order to cumulate the ions at the dielectric/semiconductor interface and the applied electric fields are close to user conditions [2]. Finally, the measurements are carried out at different temperatures, which is important for the study of thermally activated processes. In this
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