Mechanistic study of ultralow k-compatible carbon dioxide in situ photoresist ashing processes. II. Interaction with preceding fluorocarbon plasma ultralow k etching processes

Process interactions between fluorocarbon (FC) plasma ultralow k (ULK) dielectrics etching followed by carbon dioxide (CO₂) in situ photoresist (PR) ashing on ULK damage have been studied in a dual frequency, capacitively coupled plasma reactor. Introduction of ULK trench/via sidewall damage was simulated employing blanket ULK films by exposing them in a non-line-of-sight fashion in a small gap structure to the plasma environment. ULK damage was quantified using the dilute hydrofluoric acid (0.5%/15 s) selective etching method. CO₂ in situ ashing processes showed a chamber memory effect due to prior FC plasma etching, significantly increasing damage of pristine ULK films. For ULK plasma etching/PR ashing process sequences, ULK material surfaces were modified by FC plasma etching prior to the CO₂ plasma exposure. X-ray photoelectron spectroscopy studies showed that the modifications consisted primarily of 1–2 nm FC coverage of the ULK. This FC deposit remained on the ULK surfaces during in situ CO₂ processing and provided protection of the underlying ULK material. PR-patterned ULK structures were also processed employing the same processing conditions. The results obtained from the characterization of the resulting trench structures support the findings obtained with blanket films. CO₂ in situ PR ashing processes performed at low pressure (10 mTorr) and enhanced by rf biasing provided a good combination of high PR stripping rate and low ULK damage introduction.