Invited Paper PS-MoM3
Plasma Challenges of Porous SiOCH Patterning for Advanced Interconnect Levels

Monday, October 20, 2008, 9:00 am, Room 304

In CMOS technology, one of the dominant strategies to achieve future generation of ultra low-k interlayer dielectric (ILD) materials with a dielectric constant close to 2.2 is to introduce porosity into a SiOCH matrix. For the integration of porous SiOCH in damascene structures, the most important challenges are: 1) to manage profile control of narrow features (sub-75 nm trenches and vias), 2) to minimize the plasma-induced damages (modification and surface roughness) and 3) to prevent barrier diffusion into the porous SiOCH. In this work, we will address the damages (modification and surface roughness) induced by the etching and ashing plasmas on both blanket and patterned wafers. The film modification and surface roughness induced by fluorocarbon, reducing, and oxidizing plasmas have been characterized by using infrared spectroscopy, ellipsometry, atomic force microscopy techniques. The results will be presented and discussed in terms of mechanisms of film modification and formation of surface roughness. Experiments will also focus on the profile control of narrow p-SiOCH trenches using different masking strategies (metal hard mask versus organic mask). Plasma etching conditions have been optimized for both type of mask approaches to achieve sub-75 nm patterns using scanning electron microscopy and chemical topography analyses by X-ray photoelectron spectroscopy. We have shown that the organic hard mask exhibits better patterning capability in terms of trench profile control. The use of metallic hard mask can lead to profile distortion and process drift induced by metal contamination on the patterned structures and on the reactor walls of the etcher, respectively. Post etching treatments like reducing (NH₃, H₂/He, CH₄…) and oxidizing (O₂) plasmas have also been investigated on both blanket and patterned wafer to limit the barrier diffusion. We have shown that the barrier diffusion can be strongly limited if the ashing plasma generates a modification and densification of the p-SiOCH material surface. In conclusion, a delicate trade-off has to be found between the modification of the porous SiOCH film and the limitation of the barrier diffusion in order to minimize the increase in k value.