To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities ͑incident and scattered light intensities with opposite polarization͒ measured at 135°and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spherical particles again. The presence of strong cross-polarization intensities is accompanied by low-frequency instabilities detected on the scattered light intensities and plasma emission. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under our experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution.
The absolute concentration of fluorine atoms (F), a parameter of great importance for the characterization and modeling of etching plasmas, was measured by means of threshold ionization mass spectrometry in a CF4 microwave plasma (p=15–100 mTorr). The kinetics of these atoms and those of CF2 and CF3 radicals were studied by pulsing the plasma and time-resolved detection of these radicals with mass spectrometer. Sticking coefficients of F atoms on the different surrounding surfaces were estimated, as a function of the discharge parameters and the nature of the surfaces interacting with the plasma. It was found that the sticking of F atoms on hexatriacontane polymer surface is highly activated by the plasma generated ions and/or ultraviolet radiations.
The positive ions and neutral radicals arriving at the earthed walls of a capacitively-coupled radio-frequency pure CF4 plasma were analyzed using a quadrupole mass spectrometer adapted for high masses. Experiments were performed at 50 and 200 mTorr, in an empty reactor and with Si and SiO2-coated Si substrates on the powered electrode. High mass ions and neutrals were detected, up to 500 and 300 amu, respectively. The abundance of high-mass species was greatest in the presence of silicon wafers and at higher pressure. The observed ion masses can be separated into distinct series, originating from different initial bases to which successive CF2 units have been added. We, therefore, propose that these high-mass species are the result of a gas phase polymerization process consisting of CF2 addition reactions, in agreement with a model proposed recently by our group. The influence of a silicon substrate derives primarily from the strong decrease that it induces in the concentration of F atoms, which otherwise limit the concentration of CF2 and of chain initiating species.
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