2-Dimensional analysis of plasma ashing damage induced by oxygen-based plasmas along nanopores in SiOCH film for a nanoscale back-end of line process

In this work, the ashing damage induced by oxygen-based plasma, such as O₂ and CO₂ plasma, in low-k porous SiOCH (p-SiOCH) film with nanoscale pores is quantitatively analyzed to estimate the structural deformation of low-k via sidewalls during the plasma ashing process. A model of the ashing damage caused by oxygen radicals in the plasma is developed on the basis of the diffusion of oxygen radicals and their chemical reactions with the film surface along the nanoscale pores in the sidewall. The depth of the damaged sidewall regions of patterned p-SiOCH film is calculated based on the model. For patterned via structures formed by the plasma etching process, plasma ashing damage exhibits a linear characteristic along a via, with more plasma damage at the top of the via than at the bottom. In a via with a depth of 250 nm, the depth of the damaged region on the sidewall is calculated to be approximately 18.32 nm and 11.35 nm at the top and the bottom of the via, respectively. Real-life ashing damage to the sidewall is experimentally verified using the plasma ashing process for low-k via structures which have the same dimensions as those used in the calculations. There is clear agreement between the calculations and the results from electron energy loss spectroscopy.