Modeling of inductively coupled plasma SF6/O2/Ar plasma discharge: Effect of O2 on the plasma kinetic properties

Abstract

A global model has been developed for low-pressure, inductively coupled plasma (ICP) SF6/O2/Ar mixtures. This model is based on a set of mass balance equations for all the considered species, coupled with the discharge power balance equation and the charge neutrality condition. The present study is an extension of the kinetic global model previously developed for SF6/Ar ICP plasma discharges [Lallement et al., Plasma Sources Sci. Technol. 18, 025001 (2009)]. It is focused on the study of the impact of the O2 addition to the SF6/Ar gas mixture on the plasma kinetic properties. The simulation results show that the electron density increases with the %O2, which is due to the decrease of the plasma electronegativity, while the electron temperature is almost constant in our pressure range. The density evolutions of atomic fluorine and oxygen versus %O2 have been analyzed. Those atomic radicals play an important role in the silicon etching process. The atomic fluorine density increases from 0 up to 40% O2 where it reaches a maximum. This is due to the enhancement of the SF6 dissociation processes and the production of fluorine through the reactions between SFx and O. This trend is experimentally confirmed. On the other hand, the simulation results show that O(3p) is the preponderant atomic oxygen. Its density increases with %O2 until reaching a maximum at almost 40% O2. Over this value, its diminution with O2% can be justified by the high increase in the loss frequency of O(3p) by electronic impact in comparison to its production frequency by electronic impact with O2.

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“…As the SF 6 gas flow increases, the amount of O 2 in the chamber increases, and the ratio of O 2 in the total gas increases. Since O 2 gas has a lower electronegativity than SF 6 gas, an increase in O 2 gas leads to an increase in electron density [45]. For this reason, the increase of O 2 increases the F radical related to Si etch, and the etch rate increases as shown in Figure 5 [46].…”

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“…The variation of the effective fluorine and oxygen fluxes with O 2 content in the feed gas was determined by combining literature dependencies and fits of the simulated feature profiles. First, the work of Pateau et al 49 was used to set the fluorine flux as a function of oxygen in the feed gas. Accordingly, the baseline flux, determined from simulations of Fig.…”

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“…Panels (a-c) of Fig. 4 show SEM micrographs of the silicon nanowire arrays with different etching times (30,45, and 60 min). As can be seen in Fig.…”

“…10,[27][28][29] As one widely-used method for semiconductor processing, the ICP etching method has been applied, with several advantages, including low damage, high etching rates, high anisotropy, and high selection ratio. 30 The ICP method is a very complex physical and chemistry process, which is composed of two components: one is the interaction between the free radicals, metastable particles, and atoms by the inductively coupled grow discharge of etching gas; the other is the interaction between the active particles and the surface of a sample. 31 The main physical process is the ion bombardment on the surface, which has an auxiliary function for the chemical reaction rather than just the pure physical process of the sputtering etching.…”