Linewidth-narrowing due to 193 nm resist deformation during etch of spin-on low-k dielectrics

In this article a linewidth shrink of at least 20% due to deformation of a 193 nm-photo resist (PR) during etch is presented. The deformation of the resist takes place mainly at the top, resulting in an overhang and a decreased linewidth during single damascene (SD) etching. The effect of chemistry, pressure and power used in the dry etch process and PR coverage on PR deformation and sidewall slope of the hard mask (HM) has been investigated. Higher PR coverage and a polymerizing chemistry like Ar/CH₂F₂/O₂ gives significant 193 nm PR deformation, resulting in a more sloped sidewall. An increase of the ion bombardment factor through a decreased pressure reduces PR deformation and sidewall slope slightly. 193 nm PR deformation begins already at the plasma ignition step; it depends on the masses of the reactant chemistry as ion bombardment source. The use of a N₂ plasma during ignition prevents 193 nm PR deformation during subsequent etching resulting in straight sidewall of HMs, even with polymerizing chemistry.