Influence of moisture on BCN (low-K) film for interconnection reliability

The integration of low dielectric constant (low-K) interlayers and Cu wiring is necessary to produce next-generation LSI devices. Low-K films of porous type have been investigated to reduce a dielectric constant (K value). However, most porous low-K materials have faced a serious problem of water incorporation during the wet processes used in making the interconnections. Thus, the influence of moisture on boron carbon nitride (BCN) films is important to investigate. To study water-treated BCN films, we measured the current-versus-voltage (I–V) and capacitance-versus-voltage (C–V) characteristics of BCN films, using an MIS (mercury electrode/BCN/Si substrate) structure. We found that both the leakage current and dielectric constant of BCN films decrease as the film's carbon-composition ratio increases. D₂O detection using thermal desorption spectroscopy (TDS) reveals that BCN films with carbon-composition ratios greater than 30% can suppress the incorporation of water into the film. Desorption of hygroscopic water from the BCN film occurred at temperatures as low as 390 °C, which is a normal LSI-production process temperature. The use of BCN film appears to resolve the serious problem of water incorporation into the porous low-K materials. In addition, we have investigated a conduction mechanism resulting from the water protons, based on the frequency dependence of the BCN film impedance before and after water treatment.