The scaling limit of plasma enhanced chemical vapor deposited (PECVD) ultrathin(5-35 nm) silicon carbon nitride (SiCNH) dielectric as an oxidation and Cu diffusion barrier for damascene process is explored. The SiCNH cap's electrical properties, oxidation barrier performance, and the compositional depth profile analysis results showed that the scaling of the SiCNH cap is limited to 25 nm thickness. Without additional changes in current optimal SiCNH cap, 25 nm is the minimum required thickness for a reliable SiCNH cap in sub-30 nm Cu BEOL devices.

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As integrated circuits for high performance CMOS devices scale down to ≤ 10 nm dimension, further reductions in cap thickness to reduce capacitance are required for the Cu barrier while maintaining sufficient mechanical strength, low leakage, high dielectric breakdown, and fabrication integration robustness. This paper presents the development of a second generation robust low-hydrogen SiCN films to enable cap thickness reduction to ≤ 10 nm by simply altering/reducing the hydrogen concentration in the SiCN film. This is achieved by the simple addition of hydrogen precursor in the plasma deposition chemistry.

A multilayer SiN barrier film with high breakdown field and low leakage current is developed for Cu low-k interconnects and is compared with the SiCNH barrier film used in previous technology nodes. Ultrathin SiN barrier cap films also provide high conformality and fill recessions in Cu lines as observed after CMP. The conformal ultrathin (8-14 nm) multilayer SiN cap is robust with higher breakdown field, lower leakage and forms a good oxidation barrier. The electromigration activation energy for a SiN cap layer of 10-12 nm dielectric thickness is about 0.9 eV.

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