Kurt H. Becker

Absolute cross sections for the dissociative electron impact ionization of the CFx (x = 1-3) free radicals

Abstract We studied the dissociative ionization of the CFx (x = 1−3) free radicals by electron impact and measured absolute partial cross sections and appearance energies for the formation of the various fragment ions. Fast beams (3–3.5 kV) of CF3, CF2 and CF were prepared by near-resonant charge transfer of CF+3, CF+2 and CF+ with Xe under conditions where the neutral beams contained primarily ground state ions with little vibrational excitation (0.5 eV or less). Absolute cross sections for the various molecular fragment ions were measured from threshold to 200 eV with peak cross sections of up to 1.3 A2. The cross sections for the formation of the atomic C+ and F+ ions were found to be small (0.3 A2 or less) except for the F+ cross section from CF2. The measured appearance energies indicate that the fragment ions are formed with excess kinetic energies ranging from essentially zero to about 3 eV per fragment. The CF+ cross section from CF2 shows a second onset which corresponds to the double positive ion formation CF2 → CF+ + F+. Extensive ion trajectory calculations were carried out in order to quantify the collection efficiency of our apparatus for fragment ions formed with excess kinetic energy.

Electron impact ionization of ( x = 1 - 4)

We report measurements of absolute cross sections for the electron-impact ionization and dissociative ionization of the deuterated methane molecule and the (x = 1 - 3) free radicals from threshold to 200 eV using the fast-neutral beam technique. We used the deuterated rather than the protonated target species to facilitate a better separation of the various product ions from a given parent molecule in our apparatus. Good agreement was found between our results and the most recent measurements in . Our results for and agree well with earlier measurements carried out under different experimental conditions. The present results for the CD free radical are the first ionization cross section measurements for this target. A common feature of all four targets studied in this work was a dominant parent ionization cross section with essentially the same absolute value of 1.6 - at 70 eV. A comparison of the experimentally determined total single ionization cross sections with calculated cross sections using a modified additivity rule showed very good agreement for all four targets.

Electron impact ionization of the NF3 molecule

Abstract We report measurements of the absolute cross sections for the electron-impact ionizaton of the NF 3 molecule from threshold to 200 eV. Absolute values and shapes for the NF 3 parent ionization cross section were obtained independently in two different laboratories using two different experimental techniques. The agreement was better than ±8%. At 70 eV, the absolute parent NF 3 ionization cross section is 0.35 ± 0.06 A 2 . The dissociative ionization of NF 3 was studied primarily using the fast-beam technique. Absolute cross sections for the formation of the fragment ions NF + 2 and NF + were found to be 1.05 ± 0.20 A 2 (NF + 2 ) and 0.7 ± 0.15 A 2 (NF + at 70 eV. Two channels contribute to the observed NF + ion signal, the single positive ion formation NF 3 → NF + + 2F and the positive ion pair formation NF 3 → NF + + F + + F with an appearance energy of 36.5 ± 1.0 eV. While the NF + 2 fragment ions are formed with little excess kinetic energy for impact energies near threshold, the NF + fragment ions are formed with a broad distribution of excess kinetic energies ranging from essentially zero to about 4 eV. Cross sections for the formation of the atomic fragment ions F + and N + were found to be small with a maximum value of 0.3 A 2 for F + (at 70 eV) which can be attributed primarily to the double positive ion formations NF 3 → NF + + F + + F. The upper limit for the N + cross section from NF 3 is 0.1 A 2 at 70 eV.

Measured and calculated absolute total cross-sections for the single ionization of CFx and NFx by electron impact

Abstract Various additivity rules and the Deutsch—Mark (DM) formalism have been used to calculate total absolute electron-impact cross-sections for single ionization of the CF x ( x = 1–3) free radicals, the NF x ( x = 1,2) free radicals and the NF 3 molecule. A comparison is made with experimentally determined total single ionization cross-sections which have been obtained from recently measured absolute partial ionization cross-sections for the parent and dissociative ionization of these species. The overall best agreement between the measured and the calculated cross-sections in terms of the absolute values, the shapes and the cross-section ordering was obtained using a recently proposed “new” additivity rule. Common trends and tendencies in the ionization cross-sections within each class of targets, CF x and NF x , and between the two target families CF x and NF x are highlighted and a comparison will be made with the previously measured and calculated ionization cross-sections for the SiF x ( x = 1–3) free radicals.

Semiclassical calculations of the cross section for electron-impact ionization of

The semiclassical Deutsch - Mark (DM) formalism for the calculation of absolute cross sections for the single ionization of atoms has been extended to the calculation of the total single ionization cross section of the fullerene . The present calculation uses a Mulliken population analysis in which the outermost 120 orbitals are represented as linear combinations of the atomic C(2s) and C(2p) orbitals and no contributions from the more tightly bound C(1s) electrons have been considered. Detailed comparisons are made with available experimental data. Calculated cross sections are considerably larger (and the cross section curve slightly different in shape) than the measured ones. This indicates that the DM formalism (along with other calculation schemes based on an additivity concept) cannot without appropriate corrections be applied to targets with a complex structure such as .

DBD-based VUV source for advanced photolithography

Summary form only given, as follows. As the semiconductor industry pushes toward smaller and smaller chip feature size (below 0.1 /spl mu/m), shorter and shorter wavelengths are sought for the photolithographic process. We present a novel deep UV source based on a high-pressure, cylindrical DBD discharge, for advanced photolithography applications. The discharge unit consists basically of a hollow tube made of a dielectric material with two loop-electrodes wrapped around the outside wall of the tube. The discharge is generated inside the tube by means of a 13.56 MHz RF source. For good RF power transfer, an impedance matching network is introduced between the RF source and the discharge unit. Emissions at two wavelengths, 130 nm and 121.6 nm, are of particular interest. To generate 130 nm radiation, argon with a small admixture of oxygen (less than 0.1%) was used. Resonant energy transfer from argon dimers to atomic oxygen allows the emission of oxygen triplet lines around 130 nm. To generate 121.6 nm radiation, neon with a small admixture of hydrogen (less than 0.1 %) was used. The hydrogen Lyman-/spl alpha/ line at 121.6 nm was emitted via near-resonant energy transfer between neon excimers and H/sub 2/, which leads to the dissociation of H/sub 2/ and the excitation of atomic hydrogen. Spectra, as measured by a 0.2 m McPherson Scanning Monochromator (1200 G/mm, 0.1 nm resolution), will be presented. The influence of the operating pressure, gas mixture ratio, and the applied RF power on the emission spectra, the emitted optical power, and the stability of the source will be discussed.

Electron - Molecule Collision Cross Sections for Etching Gases

The purpose of this article is twofold. Firstly, we will review the current status of electron - molecule collision cross sections for those etching gases that are most commonly used as the reactive constituents of processing plasmas. This includes a discussion of (1) what are the molecules for which cross section data are needed most urgently and (2) what are the particular cross sections that are needed for the various target molecules. Secondly, we will discuss some specific aspects of dissociative electron collisions with the reactive constituents of processing plasmas, since the dissociation of the feedstock molecules in a discharge mixture induced by electron impact plays a key role in any effort to understand and to model the complex processes in the plasma.

Electron‐impact ionization of molecules of interest to processing plasmas

This paper reviews the recent developments in the measurement of absolute partial cross sections for the ionization and dissociative ionization of molecules and free radicals of interest to low‐temperature processing plasmas. In addition to a discussion of selected recent results, this paper will highlight experimental challenges such as the need to develop techniques for the production of unstable target species such as free radicals and the influence of discrimination effects arising from the formation of energetic fragment ions on the measurement of dissociative ionization cross sections. Lastly, an attempt is made to relate measured molecular ionization cross sections to realistic plasma applications. As an example, we will discuss a collision‐induced decomposition scheme of the Si‐organic molecule tetramethylsilane (TMS), which is used in plasma deposition applications, based on recently measured partial ionization cross sections.