Effects of plasma treatment on the high frequency characteristics of Cu/Ta/hydrogen silsesquioxane (HSQ) system and electrical behaviors of Cu/Ta/HSQ/Pt MIM capacitors

With the increasing of the operating frequencies, insertion loss, signal propagation delay, and parasitic coupling capacitance become the significant problems. Small capacitance (C) between interconnects is required to reduce the crosstalk, insertion loss, and RC delay associated with the metal interconnect system. Therefore, the interconnect with low dielectric constant (k) material is required. Implementation of Cu/low-k dielectric is used for reducing insertion loss, RC delay, crosstalk noises, etc. In this work, Cu-hydrogen silsesquioxane (HSQ) systems are studied. Ammonia (NH₃) plasma is employed for the nitridation of HSQ. The effects of NH₃ plasma treatments on the high frequency characteristics (100 MHz to 20 GHz) of the interconnect structure Cu/Ta/HSQ and electrical behaviors of Cu/Ta/HSQ/Pt MIM capacitors are evaluated.Auger electron spectroscopy (AES) results suggest the diffusion of oxygen and copper atoms during copper annealing. This raises resistance of Cu interconnect and increases the conductance of the HSQ films. Hence, 400 °C-annealed Cu/Ta/HSQ interconnect systems become lossy at high frequencies (>2 GHz). Ammonia (NH₃) plasma bombardments break some of the Si-H bonds and the resulting dangling Si bonds increase the moisture absorption. Meanwhile, NH₃ plasma treatments reduce the leakage current by passivating the Si dangling bond and forming silicon nitride. The absorption of moisture and/or the formation of SiN_x result in high dielectric constant of HSQ after prolonged NH₃ plasma bombardment. The dielectric constant of HSQ decreases and then increases with the increase of NH₃ plasma treatment time and a minimum dielectric constant of 2.2 is obtained after 50 s NH₃ plasma treatment at 200 W. Among various specimens in this study, the smallest insertion loss is 1.97 dB/mm at 20 GHz for the 400°C-annealed Cu/Ta/HSQ (NH₃-plasma-treated for 50 s). Appropriate NH₃-plasma bombardment helps to form a thin SiN_x barrier layer which prevents the diffusion of oxygen without increasing the dielectric constant of the Cu-HSQ interconnect system. The leakage currents versus electric field characteristics suggest that a Schottky emission dominate conduction mechanism.