Mass spectrometric measurements in inductively coupled CF₄/Ar plasmas

Abstract

Positive ion fluxes, mean ion energies and ion energy distribution functions in low pressure CF 4 /Ar plasmas have been measured. The experiments were conducted in a Gaseous Electronics Conference cell using an inductively coupled plasma device powered by a 13.56 MHz radiofrequency (rf) power source. The measurements were made at 200 and 300 W of input rf power and at 10, 20, 30 and 50 mTorr gas pressures for three gas mixtures: (i) 20% CF 4 : 80% Ar, (ii) 50% CF 4 : 50% Ar and (iii) 80% CF 4 : 20% Ar. A Langmuir probe was also used to measure plasma parameters such as n e , n + i and electron energy distribution functions (EEDF) which were subsequently used to reconcile the mass spectrometer data. CF + 3 is the most dominant fluorocarbon ion product of the plasma, followed by CF + 2 and CF + . Ar + is also detected in significant amounts with its relative flux increasing with the increase in Ar content in the gas mixture. Significant amounts of etch products, SiF +x /COF + x (x = 0-3), of the quartz window were also detected. The fluorocarbon ions are produced by direct electron impact and by ion-molecule reactions between Ar + and CF 4 as well as between CF + 3 and CF 4 . However, the concentrations of CF + 2 and CF + are much larger than that which can be possibly produced from these two processes. The available cross-section data suggest that the direct electron impact ionization of the fragment neutrals and negative ion production by electron attachment may be responsible for the increase in the concentrations of the minor ions. F − densities, estimated by using the measured EEDF and positive ion flux data and the available cross-section data, agree well with the published experimental data.

Parallel 2D Axisymmetric Fluid Modeling of CF4 Discharge in an Inductively Coupled Plasma Source During SiO2 Etching

“…of quartz window were also detected by Rao et al [30,31] and Zhou et al [32] Hikosaka et al [33] used a quadrupole mass spectrometer (QMS) to measure gas composition in a highpower CF 4 discharge. CO and SiF 3 were found due to the etching of quartz (SiO 2 ) window, which significantly deteriorated the etching selectivity of SiO 2 in an ICP reactor.…”

“…Results show that these species concentrated in the central core region due to electron related ionization from feedstock gas CF 4 (F01$F10) with CF 3 which is similar to those observed by some experiments. [30,41] In addition, the CF 3 þ concentration not only peaks in the central core region but also in the region near gas inlet because of its low threshold energy of dissociative ionization (14.8 eV). Figure 11 shows the spatial distributions of the concentrations of oxygencontaining positive charged species, including O þ , O 2 þ , and CO þ .…”

“…The concentrations of the charged and neutral species averaged spatially over the core region of the reactor are presented in Figures 17 and 18 estimated by Rao et al [30] through a simple chemical kinetic model with the use of some experimental data; however, its validity needs to be confirmed. In addition, except the CF 4 which is the feedstock gas, F is the most dominant radical species with a concentration of $10 20 m À3 that explains why the coverage of fluorine on the substrate is the largest among all species.…”

High-Pressure Study of Ion-Molecule Reactions in the Mixture of Carbon Tetrafluoride and Argon

“…From the applied point of view, knowledge of both the product fractional abundance and the reaction rate coecient is fundamental for the modeling and optimization of plasmas for industrial applications [7]. CF 4 is a commonly used gas in radiofrequency (rf) plasmas for etching SiO 2 (typically, mixtures of uorocarbons and argon are used in plasma etching), depositing silicon oxide and silicon nitride layers and for plasma chamber cleaning processes [1,1317].…”

Mass spectrometric study of discharges produced by a large-area dual-frequency–dual-antenna inductively coupled plasma source

“…This is the reason why we chose CF 4 as an investigation gas to understand the influence of power and frequency levels on IEDs. CF + 3 is found as the major ionic species in the discharge [38]; however, other fluorocarbon ions (CF + 2 , CF + ) are also present in significant number. The main mechanism responsible for the production of fluorocarbons is the direct electron impact ionization of the parent molecule (CF 4 ), and it produces fluorocarbons in the order CF + 3 > CF + 2 > CF + .…”