Remote H2/N2 plasma processes for simultaneous preparation of low-k interlayer dielectric and interconnect copper surfaces

This study focuses on the simultaneous plasma treatment of interlayer dielectric (ILD) and chemical mechanical polished (CMP) Cu surfaces using N2/H2 plasma processes. The modifications induced by the gas chemistries are investigated for two ILD films with different porosities and carbon concentrations. H atoms and radicals in the plasma react with the carbon groups leading to carbon removal for both of the ILD films. Fourier transfer infrared (FTIR) spectra show a greater fractional reduction of CH3 in the high porosity ILD compared to the low porosity ILD. Results indicate that an N2 plasma forms an amidelike layer on the surface, which apparently leads to reduced carbon abstraction from an H plasma process. In addition, FTIR spectra indicate the formation of hydroxyl (SiOH) groups following the plasma exposure. Increased temperature (380 °C) processing leads to a reduction of the hydroxyl group formation compared to ambient temperature processes, and the dielectric constant is increased by a smaller amount. It appears that the increase of the dielectric constant is mainly attributed to moisture uptake rather than network topography change due to carbon loss. The plasma experiments were repeated with CMP Cu surfaces at both ambient temperature and 380 °C. The carbonate contamination was removed by an H2 plasma process at elevated temperature while the CC and CH contamination was removed by an N2 plasma process at elevated temperature.