Air-Gaps for High-Performance On-Chip Interconnect Part I: Improvement in Thermally Decomposable Template

The incorporation of air-cavities (i.e., air-gaps) as the intralevel dielectric in integrated circuits (ICs) can provide an ultralow-k solution, especially at the 32 nm technology node and beyond. Air-gaps can be created by the templating method using norbornene (NB)-based sacrificial polymers. However, it has been found that the hardness and modulus of the templating material is critical to achieving mechanical fidelity of the structure during processing. As a result, stiffer sacrificial polymers lead to higher yield. In this study, tetracyclododecene (TD)-based sacrificial polymers were investigated and compared with norbornene-based (NB)-based polymers. Nanoindentation experiments showed that thin films of TD-based sacrificial polymers were harder than NB-based sacrificial polymers. The effect of the modulus and hardness on the process repeatability was quantitatively evaluated by comparing the straightness of 50-nm-wide lines of TD- and NB-based sacrificial polymers. It was shown that the TD-based polymer structures were straighter and had better reproducibility than those of NB-based polymers due to an increase in hardness and modulus. The thermal decomposition properties of TD-based polymers were similar to their NB-based counterparts. Both TD- and NB-based polymers were thermally stable at 300°C and the decomposition residues were less than 1% of the original weight. The thickness of the residue (solid reaction byproducts) from thin TD films was as low as 2.1 nm (depending on the atmosphere quality) and the residue was hydrophobic.