Downstream etching of silicon nitride using continuous-wave and pulsed remote plasma sources sustained in Ar/NF3/O2 mixtures

Abstract

Remote plasma sources (RPSs) are being investigated to produce fluxes of radicals for low damage material processing. In this computational investigation, the properties of a RPS etching system are discussed where an Ar/NF3/O2 gas mixture is flowed through an inductively coupled plasma source into a downstream chamber containing a silicon nitride coated wafer. The plasma is largely confined in the RPS due to the highly attaching NFx (x = 1–3) and an isolating showerhead although a weak ion-ion plasma maintained by [NO+] ≈ [F−] leaks into the downstream chamber. The etching of silicon nitride proceeds through iterative removal of Si and N subsites by isotropic thermal neutrals. When the fluxes to the wafer are rich in fluorine radicals, the etch rate is limited by the availability of NO molecules and N atoms which remove N subsites. As power deposition increases with continuous-wave excitation, the etch rate increases almost linearly with the increasing fluxes of NO and N atoms, as production of NO through endothermic reactions is aided by increasing gas temperature. Production of N atoms through electron impact dissociation of NO and NFx is aided by the increasing electron density. Similar trends occur when increasing the duty cycle during pulsed excitation. Addition of a plenum between the RPS and the downstream chamber aids in lateral diffusion of radicals before passing through the final showerhead and improves the uniformity of etching.

Vacuum ultraviolet-absorption spectroscopy and delocalized plasma-induced emission used for the species detection in a down-stream soft-etch plasma reactor

“…These authors also provide the wavelength dependent absorption cross section, from which the absorbance can be converted to the density of HF in the DSC by using Eq. (8). The deduced partial pressure of HF in the example presented in Fig.…”

“…Si, SiN and SiO2), which can be achieved in F-based RPS plasmas. NF3 is typically used as F source due to its high cross section for dissociative electron attachment [8].…”

Current status and nature of high-frequency electronegative plasmas: basis for material processing in device manufacturing

“…It is estimated that even in an ICP highly diluted system in Ar(90%)/NF 3 (5%)/O 2 (5%) at 50 mTorr, the negative ion F − accounts for the majority of negative charges in the afterglow phase. 49) Attention will be paid to the recombination of negative ions with the positive ion of the diluted noble gas atom. Table V shows typical recombination rate constants between heavy ions.…”

Rethinking surface reactions in nanoscale dry processes toward atomic precision and beyond: a physics and chemistry perspective

“…When the production of N atoms is increased through the electron impact dissociation of NO and NF x , which increases electron density, the etching rate increases almost linearly with the increasing fluxes of NO and N atoms, as production of NO through endothermic reactions is aided by increasing gas temperature. 53) The self-limited etching of SiN has been performed in a commercial plasma etching chamber. The process consists of two sequential steps, namely surface modification in H 2 plasma followed by the removal of the modified layers in fluorinated plasma.…”