F. Cramarossa

Spectroscopic diagnostics of CF4‐O2 plasmas during Si and SiO2 etching processes

The emission intensities in the range of 2000–8000 A of CF, CF2, O, F, CO, CO+, and CO2 produced in CF4/O2 radio‐frequency discharges, operated at 1 Torr of pressure and 50 W of power input, have been used to follow the etching process of Si and SiO2, as a function of the CF4/O2 feed composition. The addition of small amounts of nitrogen or argon to the plasma mixtures has permitted the determination of the effect of the oxygen addition to the gas feed on the electron densities of the plasma for a wide range of electron energies. The relative concentration profiles of F and O, as well as of CO and CO2, have been determined with this technique, as a function of the oxygen content in the feed. The important role played by atomic F as active etchant for both Si and SiO2 substrates has been confirmed.

Mechanisms of etching and polymerization in radiofrequency discharges of CF4–H2, CF4–C2F4, C2F6–H2, C3F8–H2

Some results obtained during the etching of Si or the deposition of fluorocarbon films over Si substrates uncoupled from ground in rf plasmas fed with CF4–H2, C2F6–H2, C3F8–H2 and CF4–C2F4 mixtures are presented. The polymerization process is explained on the basis of a mechanism which involves CF and/or CF2 radicals as building blocks as well as an activation of the polymer surface by means of charged particle bombardment. It is definitively proved that the etch rate of Si depends only on the F‐atom concentration, independent of conditions in the various feeds.

Mechanisms of deposition and etching of thin films of plasma‐polymerized fluorinated monomers in radio frequency discharges fed with C2F6‐H2 and C2F6‐O2 mixtures

Deposition and etching of thin plasma‐polymerized fluorinated monomers have been studied in discharges fed with C2F6‐H2 and C2F6‐O2 mixtures, respectively. A parallel plate reactor with thermostated electrodes has been utilized for the present study. The experiments have allowed us to ascertain the role of positive ions and of radicals, as well as the effect of pressure and substrate temperature, on the mechanism of deposition. The mechanism of etching has also been investigated, and it has been found that both O and F atoms contribute to the process through overall first‐order kinetics. Conditions for a selective etching of noncross‐linked films with respect to cross‐linked ones have also been found.

Diagnostics and decomposition mechanism in radio-frequency discharges of fluorocarbons utilized for plasma etching or polymerization

Optical emission (180–800 nm) and mass spectroscopy have been used to study the CF4, CF4+O2, C2F6, C2F6+H2, CF3Cl, and C2F4 decomposition in radio-frequency discharges. The analysis of the stable and unstable discharge products has allowed the suggestion of decomposition channels for the various gases and to classify the fluorinated gases according to their predominant etching or polymerizing characteristics on the basis of the active species present in the plasma. A new broad emission continuum centered at λ=290 nm (FWHM=66 nm) has also been identified and it has been tentatively assigned to CF+2.

Polymer film formation in C2F6H2 discharges

Abstract Thin fluoropolymer films deposited in an r.f. discharge fed with C 2 F 6 H 2 mixtures were studied. The effect of the electrical characteristics, the substrate temperature and the feed composition on both the chemical structure of the film and on the growth mechanism were analysed. It was found, in particular, that the structure of the film is affected by the H 2 concentration in the feed and by the discharge voltage and current values and that the polymerization rate decreases with temperature after a threshold.

The use of “actinometer” gases in optical diagnostics of plasma etching mixtures: SF6-O2

The spectroscopic emission intensities from excited F atoms in SF6-O2 discharges at 1 torr have been correlated to the densities of atoms in their ground electronic state by measuring the excitation efficiencies of the electrons in the energy range 11 to 17 eV with a method which essentially consists in the analysis of the emission of Ar or N2, added as “actinometer” gases to the discharge mixtures. The general applicability of the method has been tested by a direct titration of F atoms with chlorine. The spectroscopic analysis has allowed the determination of useful information on the trends of both the electron densities and their energies as a function of the oxygen percent in the feed.

Kinetic and spectroscopic analysis of NH3 decomposition under R.F. Plasma at moderate pressures

The plasma decomposition of NH3 has been studied as a function of the residence time, power input, and pressure. The process follows apparently zero-order kinetics, which can be interpreted on the basis of a kinetic mechanism involving as initial step the rupture of an N-H bond from vibro-rotationally excited modecules. Simultaneous spectroscopic observations of the emission light due to electronically excited NH2, NH, H, and N2 have been used to confirm the suggested mechanism and to show that NH2 and NH are successive intermediate species and that the final step of the decomposition process is the bimolecular recombination NH+NH→N2+H2.

Optical emission spectroscopy and actinometry in CCl4-Cl2 radiofrequency discharges

Radiofrequency discharges fed with CCl4-Cl2 mixtures have been studied in the pressure range 0.3 to 0.6 torr by means of emission spectroscopic actinometry with Ar, He, and N2 as actinometers. Two different reactors, a parallel plate and a capacitively coupled tubular one, have been utilized for this study to obtain information for a large range of electron energy distributions. Analysis of the experimental results demonstrates the following: the utilization of actinometry and its range of validity, the importance of electron attachment to CClx species during the plasma decomposition process, and the effects of the presence of chlorine and “glowpolymer” in the discharge medium.

R.f. plasma deposition of amorphous silicon films from SiCl4-H2

Abstract Preliminary results on amorphous silicon films obtained by reduction of SiCl4 under hydrogen r.f. discharges at pressures between 1 and 5 Torr are presented. X- ray diffraction, IR and electron spin resonance spectroscopic techniques, optical absorption, electron spectroscopy for chemical analysis and room temperature electrical measurements were used for chemical and physical characterization of the deposited films. Chemical characterization of the films showed the presence of chlorine and hydrogen as SiH2, SiH2Cl and/or SiHCl2. Electron spin resonance measurements of a sample deposited at 430 K yielded a dangling bond density of 1016cm-3.

On the use of actinometric emission spectroscopy in SF6-O2 radiofrequency discharges: Theoretical and experimental analysis

A comparison of the results obtained by solving the Boltzmann equation with the experimental results from optical emissions obtained in SF6-O2 radiofrequency discharges, when N2, Ar, and He are also admitted as actinometers, has allowed us to explore the potentialities and limits of actinometry. The use of different actinometers also allowed us to monitor the evolution of the electron distribution functions as a function of the plasma parameters.