Effect of Small O₂ and N₂ Admixture in Ar/H₂ Remote Plasma Cleaning on SiOCH in Back-End-of-Line Cu Seed Layer Fabrication

This study investigates the effects of nitrogen (N 2 ) and oxygen (O 2 ) plasma, in addition to argon (Ar)/hydrogen (H 2 ) plasma, during remote plasma cleaning (RPC) in back-end-of-line (BEOL) integration, particularly for Cu–Mn/Co/TaN barrier-metal stacks deposited on SiOCH low-k dielectrics. The primary objective is to evaluate the role of these plasmas in removing Cu–Mn surface oxides (e.g., Cu 2 O, CuO, MnO x ) from the materials while minimizing damage to the underlying SiOCH layer. Our results show that O 2 and N 2 plasma treatments induce changes in the bonding structure of low-k materials by depleting carbon atoms and forming Si-OH bonds, leading to increased dielectric constant and moisture uptake. The dielectric constant (k-value) increased from 2.87 ± 0.05 (pristine SiOCH) to 3.00 ± 0.05 after Ar/H 2 /O 2 treatment, whereas after the Ar/H 2 /N 2 treatment, a stable k-value of 2.86 ± 0.05 was maintained, indicating a lower degree of plasma-induced damage. Furthermore, depth profile analyses using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy confirmed that Ar/H 2 /N 2 plasma effectively reduced oxygen diffusion into the Cu–Mn/TaN barrier layers, thereby mitigating oxidation-related reliability concerns during BEOL processing.