Enhancement of the Mechanical Properties of Low-k SiCOH Films by Plasma Treatment and Ultraviolet Curing

The integration of organosilicate SiCOH low-k dielectrics in back-end-of-line (BEOL) interconnect structures requires a balance between low k and sufficient mechanical robustness. Low-k films with a thickness of approximately 2800 Å were deposited on 300 mm Si wafers via plasma-enhanced chemical vapor deposition (PECVD) using diethoxymethylsilane (DEMS) and O2 at 260 °C. To investigate the effects of process engineering on film properties, the total film thickness was divided into one, two, three, five, or 10 sublayers to compare segmentation, cyclic O2/He-plasma treatment, and interleaved ultraviolet (UV) curing. The resulting films were characterized by spectroscopic ellipsometry, nanoindentation, X-ray photoelectron spectroscopy (XPS) depth profiles, and Fourier-transform infrared (FTIR) spectroscopy. Segmentation increased the k value from 3.35 to 3.66, accompanied by a non-monotonic mechanical response. Extending the plasma treatment from 1 to 20 s led to a 19.8% rise in the k value, along with respective increases of 9.4% in hardness and 16.1% in the modulus, consistent with carbon/hydride removal and oxidative densification of the silicate network. Increasing RF power from 300 to 900 W caused smaller dielectric changes while raising the hardness and modulus by 8.7% and 10.6%, respectively, indicating diminishing changes at higher applied powers. Interleaved UV curing, comprising UV irradiation and concurrent thermal treatment, reduced the thickness, increased the refractive index (RI), and maintained a lower k relative to the as-deposited films. After five UV curing cycles, the hardness and modulus reached the highest mean values of 4.6 GPa and 35.8 GPa, respectively. FTIR analysis showed systematic depletion of Si–CH3 and Si–H groups and Si–O–Si network evolution, whereas XPS showed relatively stable plateau composition but treatment-sensitive transition regions. The combined results are consistent with oxidation-related modification during plasma treatment and network reorganization during UV curing, with possible differences in the spatial extent of these processes. These results further indicate that an intermediate cycle count provides a favorable balance between dielectric and mechanical properties.