Measurement of absolute CO number densities in CH₃F/O₂plasmas by optical emission self-actinometry

Abstract

CH 3 F/O 2 inductively coupled plasmas at 10 mTorr were investigated using optical emission spectroscopy. A 'self-actinometry' method was developed to measure the absolute number density of CO that formed in reactions following dissociation of CH 3 F and O 2 in the plasma. In this method, small amounts of CO were added to the plasma, leading to small increases in the CO emission intensity. By carefully accounting for small perturbations to the plasma electron density and/or electron energy distribution, and by showing that very little of the CO added to the plasma was decomposed by electron impact or other reactions, it was possible to derive absolute number densities for the CO content of the plasma. With equal fractions (0.50) of CH 3 F and O 2 in the feed gas, the CO mole fraction as a function of plasma power saturated at a value of 0.20-0.25. As O 2 in the feed gas was varied at a constant power of 100 W, the CO mole fraction went through a maximum of about 0.25 near an O 2 feed gas fraction of 0.5. The relative CO number densities determined by 'standard' actinometry followed the same functional dependence as the absolute mole fractions determined by self-actinometry, aided by the fact that electron temperature did not change appreciably with power or feed gas composition.

Optical emission self-actinometry for measuring absolute number densities of air species diffusing into a helium atmospheric pressure plasma jet

“…Previously, we reported a 'self-actinometry' method that can be used to obtain absolute number densities of stable species in low pressure plasmas. N 2 and CO number densities were obtained in NH 3 and CH 3 F/O 2 plasmas [28,29], respectively, and were verified by independent spectroscopic measurements. In this study, self-actinometry was demonstrated under the more complex conditions encountered in atmospheric pressure plasmas.…”

Measurement of Argon emission spectral of ICP plasma using a diagnostic system based on photomultiplier tubes array

“…The reason is that other collisional processes are trivial and the density of metastables is too low to make a significant contribution to the excitation of the excited species under these conditions [9][10][11]. In a corona model for these levels, we have the electron-impact excitation from the ground-state atom, Ar(gs) + e Ar(2p1 ) + e (1) and the spontaneous radiation, Ar(2p 1 )Ar(1s 2 ) + hv…”

“…In order to understand the plasma chemistry, various plasma process diagnostic tools such as OES and Langmuir probe have been developed to quantify the concentration of reactive species in the plasma [1]. Because it is non-intrusive, inexpensive, and can be easily incorporated into an existing plasma reactor, the OES quickly gains popularity in the microelectronics industry for monitoring the plasma processing.…”