Physical aspects of plasmas for plasma-chemical applications

A review with 32 refs. defining the field of plasma chem. and stressing certain recent developments in the phys. understanding of various chem. plasmas. [on SciFinder (R)

Ionic species in a negative corona in humid air

A mass spectrometric study of a neg. corona in air showed that the most important ions that reach the anode are O3-, CO3-, and NO3-. Also, very strong clustering was obsd. wit

Decay of metastable Ne (/sup 3/P/sub 2/)-atoms

The afterglow of a Townsend discharge is used for mass spectrometrical determination of the Ne (/sup 3/P/sub 2/) decay at 77 and 295K, using the Penning ionisation of N/sub 2/ impurities as a diagnostic reactio

Plasma parameters and silicon dioxide etch rates in a carbon tetrafluoride plasma

A plane-parallel electrode discharge device, operating with CF4 at 0.05-0.5 torr, 13.5 MHz, and input power 0.05-1 W/cm2 was used to etch a SiO2 layer on a Si substrate. Electron densities, etch rates, and intensity ratios of spectral lines were detd. Insight was obtained into the geometry of the discharge and the occurrence of various species in it. [on SciFinder (R)

Measurement of the gas temperature in fluorocarbon radio frequency discharges using infrared absorption spectroscopy

The translational gas temperature was measured in 13.56 MHz radio-frequency (rf) discharges in CF4 and CHF3. Infrared absorption spectra of CF4 and CF2 were recorded using a tunable diode laser and the gas temperature was deduced from the linewidths of the absorption lines of these molecules. It is shown that linewidth measurements yield a simple and direct method to determine the gas temperature, with an accuracy up to ~ 10 K. The results obtained in CF4 and CHF3 plasmas indicate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The temperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased heating rate of the gas. Moreover, it was found that the temperature rise is significantly smaller in CHF3 than in CF4, under the same plasma conditions. This can be attributed to a higher power dissipation by chemical conversion of the parent gas in a CHF3 discharge, as compared with a CF4 plasm

Mass-resolved ion energy measurements at both electrodes of a 13.56 MHz plasma in CF4

The ion energy distributions (IEDs) at the electrodes in a capacitively coupled 13.56 MHz plasma in CF4 have been measured mass resolved with a Balzers quadrupole in combination with a home-built energy analyzer. Mass-resolved determination offers the possibility to compare the IED of different ions achieved in the same sheath. The IEDs have been determined at both the largest and the smallest electrode. Apart from the IEDs of the CF4 species, the IEDs of ionic species in plasmas in argon and nitrogen also were determined. Apart from the CF4 ionic species CF+3, CF+2, CF+, and F+, CHF+2 ions also are present in the CF4 plasma due to residual water in the reactor. Because the CHF+2 ions are not produced in the sheath and because we do not detect elastically scattered ions, the IEDs of these ions show the typical bimodal distribution for rf plasmas which corresponds to an IED of ions which have not collided in the sheath. From these IEDs we can obtain the sheath characteristics, such as the averaged sheath potential. From the IEDs of CF+n ions one can conclude that, in the sheath of the CF4 plasma, a large number of chemical reactions takes place between the CF+n ions and the neutrals

The chemistry of a CCl2F2 radio frequency discharge

A systematic study of the chemistry of stable molecules and radicals in a low pressure CCl2F2 radio frequency discharge for dry Si etching has been performed. Various particle densities have been measured and modeled. The electron density, needed as an input parameter to model the CCl2F2 dissociation, is measured by a microwave cavity method. The densities of stable molecules, like CClF3, CF4, 1,2-C2Cl2F4 and the etch product SiF4, are measured by Fourier transform absorption spectroscopy. The density of the CF2 radical is measured by means of absorption spectroscopy with a tunable diode laser. Its density is in the order of 1019 m-3. All density measurements are presented as a function of various plasma parameters. Moreover, optical emission intensities of Cl and F have been recorded as a function of plasma parameters. It appears that the feed gas (CCl2F2) is substantially dissociated (about 70%–90%) in the discharge. Based on the obtained data the dissociation rates of several molecules have been estimated. The measured total dissociation rate of CCl2F2 is 8×10-15 m3¿s-1. For this molecule the dissociation rate is substantially higher than the dissociative attachment rate (10-15 m3¿s-1). The dissociation rate for CClF3 is 2×10-15 m3¿s-1 and for CF4 about 3×10-16 m3¿s-1. The total dissociation rate of C2Cl2F4 is higher than 5 ×10-15 m3¿s-1, of which 2.5±0.5 × 10-15 m3¿s-1 is due to dissociative attachment. Furthermore it has been found that the presence of a silicon wafer strongly affects the plasma chemistry. Optical emission measurements show that the densities of halogen radicals are significantly depleted in presence of Si. Moreover, the densities of several halocarbon molecules display a negative correlation with the density of the etch product SiF4. © 1995 American Vacuum Societ