Enhancement of post-Cu-chemical mechanical polishing cleaning process for low-k substrate

The introduction of low-dielectric-constant (low-k) materials as interlayer dielectrics (ILD) to support Cu interconnects causes poor slurry removal efficiency and watermark generation in post Cu-chemical mechanical polishing (CMP) cleaning because low-k dielectric films are hydrophobic. To address these problems, the authors performed basic studies using low-k (SiOC) blank (unpattemed) substrates. Our studies have revealed that it is important to control the wettability of the SiOC surface by using a surfactant-spiked cleaning solution in order to effectively remove the large number of slurry particles adhering to the SiOC surface due to hydrophobic interaction. For watermark generation, our study has found that even the combination of ultrapure water (UPW) spin rinsing and spin drying causes a watermark to be generated on a clean SiOC surface. It is revealed that watermark generation is attributed mainly to oxygen diffusion into microdroplets left on the SiOC surface after spin drying. Fourier transform IR (FTIR) analysis indicates this Watermark to be composed of silicon oxides or silicon hydrates. The authors have also proven that watermark generation can be suppressed by using ultrapure water with N-2 gas dissolved to its saturated concentration (N-2-UPW).