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Title: Comparison of surface reactivity of CN, NH, and NH{sub 2} radicals during deposition of amorphous carbon nitride films from inductively coupled rf plasmas

Abstract

The interactions of CN, NH, and NH{sub 2} radicals with carbon nitride films during inductively coupled rf plasma deposition were measured using the imaging of radicals interacting with surfaces (IRIS) technique. The surface reactivity R for each species was obtained at various gas compositions of N{sub 2}/CH{sub 4} and NH{sub 3}/CH{sub 4} and applied rf powers. R values for CN and NH radicals ranged from 0.85 to 1.0 and 0.1 to 0.2, respectively, and show very little dependence on the gas compositions and applied power. In contrast, R values for NH{sub 2} decreased from 0.6{+-}1 to 0.2{+-}0.1 when the CH{sub 4} fraction in the plasma was increased from 0% to 70%. The essentially 100% scatter measured for NH suggests that it does not contribute significantly to film growth in these systems. The effect of ion bombardment on the R values in these systems was analyzed by applying a dc bias to the substrate. In general, R values were found to decrease when a +200 V bias was applied. Results indicate that energetic ions are important in surface production of the species studied with IRIS. The plasmas have also been characterized by mass spectrometry, including the measurements of ion energy distributions.more » Mechanisms for film deposition in these carbon nitride systems are discussed incorporating the authors' gas-phase and gas-surface interface data.« less

Authors:
;  [1]
  1. Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872 (United States)
Publication Date:
OSTI Identifier:
20979396
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films; Journal Volume: 25; Journal Issue: 2; Other Information: DOI: 10.1116/1.2699216; (c) 2007 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMMONIA; AMORPHOUS STATE; CARBON NITRIDES; CHEMICAL VAPOR DEPOSITION; COMPARATIVE EVALUATIONS; ENERGY SPECTRA; HYDROGEN; ION BEAMS; MASS SPECTRA; MASS SPECTROSCOPY; METHANE; PLASMA; RADICALS; SURFACES; TAIL IONS; THIN FILMS

Citation Formats

Liu Dongping, and Fisher, Ellen R. Comparison of surface reactivity of CN, NH, and NH{sub 2} radicals during deposition of amorphous carbon nitride films from inductively coupled rf plasmas. United States: N. p., 2007. Web. doi:10.1116/1.2699216.
Liu Dongping, & Fisher, Ellen R. Comparison of surface reactivity of CN, NH, and NH{sub 2} radicals during deposition of amorphous carbon nitride films from inductively coupled rf plasmas. United States. doi:10.1116/1.2699216.
Liu Dongping, and Fisher, Ellen R. Thu . "Comparison of surface reactivity of CN, NH, and NH{sub 2} radicals during deposition of amorphous carbon nitride films from inductively coupled rf plasmas". United States. doi:10.1116/1.2699216.
@article{osti_20979396,
title = {Comparison of surface reactivity of CN, NH, and NH{sub 2} radicals during deposition of amorphous carbon nitride films from inductively coupled rf plasmas},
author = {Liu Dongping and Fisher, Ellen R.},
abstractNote = {The interactions of CN, NH, and NH{sub 2} radicals with carbon nitride films during inductively coupled rf plasma deposition were measured using the imaging of radicals interacting with surfaces (IRIS) technique. The surface reactivity R for each species was obtained at various gas compositions of N{sub 2}/CH{sub 4} and NH{sub 3}/CH{sub 4} and applied rf powers. R values for CN and NH radicals ranged from 0.85 to 1.0 and 0.1 to 0.2, respectively, and show very little dependence on the gas compositions and applied power. In contrast, R values for NH{sub 2} decreased from 0.6{+-}1 to 0.2{+-}0.1 when the CH{sub 4} fraction in the plasma was increased from 0% to 70%. The essentially 100% scatter measured for NH suggests that it does not contribute significantly to film growth in these systems. The effect of ion bombardment on the R values in these systems was analyzed by applying a dc bias to the substrate. In general, R values were found to decrease when a +200 V bias was applied. Results indicate that energetic ions are important in surface production of the species studied with IRIS. The plasmas have also been characterized by mass spectrometry, including the measurements of ion energy distributions. Mechanisms for film deposition in these carbon nitride systems are discussed incorporating the authors' gas-phase and gas-surface interface data.},
doi = {10.1116/1.2699216},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 2,
volume = 25,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • Fluorinated silicon-nitride films have been prepared at low temperature (250 deg. C) by remote plasma enhanced chemical vapor deposition using mixtures of SiF{sub 4}, N{sub 2}, Ar, and various H{sub 2} flow rates. The deposited films were characterized by means of single wavelength ellipsometry, infrared transmission, resonant nuclear reactions, Rutherford backscattering analysis, and current-voltage measurements. It was found that films deposited without hydrogen grow with the highest deposition rate, however, they result with the highest fluorine content ({approx}27 at. %) and excess of silicon (Si/N ratio{approx_equal}1.75). These films also have the lowest refractive index and the highest etch rate, andmore » exhibit very poor dielectric properties. As a consequence of the high fluorine content, these films hydrolize rapidly upon exposure to the ambient moisture, forming Si-H and N-H bonds, however, they do not oxidize completely. The addition of hydrogen to the deposition process reduces the deposition rate but improves systematically the stability and insulating properties of the films by reducing the amount of both silicon and fluorine incorporated during growth. All the fluorinated silicon-nitride films deposited at hydrogen flow rates higher than 3.5 sccm resulted free of Si-H bonds. In spite of the fact that films obtained at the highest hydrogen flow rate used in this work are still silicon rich (Si/N ratio{approx_equal}1.0) and contain a considerable amount of fluorine ({approx}16 at. %), they are chemically stable and show acceptable dielectric properties.« less
  • We investigated reaction characteristics in a CH{sub 4}/N{sub 2} plasma for deposition of amorphous CN{sub x} thin films (a-CN{sub x}) by evaluating the change in electron density using the wave cutoff method, and the behavior of ions and radicals with an optical emission spectroscopy (OES). An inductively coupled plasma source that was 30 cm away from the substrate stage was used for the discharge. The change in electron density in the substrate region and OES spectra in the plasma-source region were evaluated to investigate both the reaction mechanism and the remote effect while varying process conditions such as rf power,more » pressure, and gas-mixing ratio. We found that the electron density in the remote CH{sub 4}/N{sub 2} plasma was closely related to recombination reactions of major ions such as N{sub 2}{sup +}, CH{sub 4}{sup +}, CH{sub 3}{sup +}, and H{sub 2}{sup +} during diffusion from the plasma source to the substrate. The electron density and optical emission of major ions and radicals in the CH{sub 4}/N{sub 2} plasma increase at higher rf power. The ratio [N]/([N]+[C]) in a-CN{sub x} films, as measured by auger electron spectroscopy, also increases with rf power since more excited N and C species are generated. For increasing pressure, the change in electron density and emission spectra showed different behavior, which arose from recombination of ions that generated more CH{sub 4}, N{sub x} (x=1,2), and CN radicals. The majority of positive ions generated from N{sub 2} species are greatly affected by the remote effect, while the majority of positive ions generated from CH{sub 4} species are not significantly influenced, since each species has different losses dependent on the pressure. A higher N{sub 2} gas fraction in the gas mixture generated more CN radicals, which resulted not only in more N incorporated into a-CN{sub x} films but also to a reduction of H passivation that retards formation of hybrid bonding between C and N in the films. These results suggest that efficient H abstraction is required to achieve more N{identical_to}C triple bonding in CH{sub 4}/N{sub 2} plasma deposition.« less
  • In an industrial inductively coupled plasma reactor dedicated to silicon etching in chlorine-based chemistry, the density of Cl{sub 2} molecules and the gas temperature are measured by means of laser absorption techniques, the density of SiCl{sub x} (x{<=}2) radicals by broadband absorption spectroscopy, the density of SiCl{sub 4} and ions by mass spectrometry, and the total gas pressure with a capacitance gauge. These measurements permit us to estimate the mole fractions of Cl, SiCl{sub 4}, and etch product radicals when etching a 200 mm diameter silicon wafer. The pure Cl{sub 2} plasma is operated in well prepared chamber wall coatingmore » with a thin film of SiOCl, AlF, CCl, or TiOCl. The impact of the chemical nature of the reactor wall's coatings on these mole fractions is studied systematically. We show that the reactor wall coatings have a huge influence on the radicals densities, but this is not only from the difference on Cl-Cl recombination coefficient on different surfaces. During silicon etching, SiCl{sub x} radicals sticking on the reactor walls are etched by Cl atoms and recycled into the plasma by forming volatile SiCl{sub 4}. Hence, the loss of Cl atoms in etching the wall deposited silicon is at least as important as their wall recombination in controlling the Cl atoms density. Furthermore, because SiCl{sub 4} is produced at high rate by both the wafer and reactor walls, it is the predominant etching product in the gas phase. However, the percentage of redeposited silicon that can be recycled into the plasma depends on the amount of oxygen present in the plasma: O atoms produced by etching the quartz roof window fix Si on the reactor walls by forming a SiOCl deposit. Hence, the higher the O density is, the lower the SiCl{sub 4} density will be, because silicon is pumped by the reactor walls and the SiOCl layer formed is not isotropically etched by chlorine. As a result, in the same pure Cl{sub 2} plasma at 20 mTorr, the SiCl{sub x} mole fraction can vary from 18% in a SiOCl-coated reactor, where the O density is the highest, to 62% in a carbon-coated reactor, where there is no O. In the latter case, most of the Cl mass injected in the reactor is stored in SiCl{sub 4} molecules, which results in a low silicon etch rate. In this condition, the Cl mass balance is verified within 10%, and from the silicon mass balance we concluded that SiCl{sub x} radicals have a high surface loss probability. The impact of the reactor wall coating on the etching process is thus important, but the mechanisms by which the walls control the plasma chemistry is much more complicated than a simple control through recombination reaction of halogen atoms on these surfaces.« less
  • Hydrogenated diamond-like Carbon (DLC) films have been deposited on Si substrates using CH{sub 4}-based radio-frequency plasmas. The films have been doped with nitrogen by addition of either N{sub 2} or NH{sub 3} into the source gas mixture, producing films with up to 16% and 25% N content, respectively. The effect of additions of Ne to these gas mixtures has been investigated as a possible method to increase the growth rate and the N-content of the films. The authors find that addition of Ne increases the film growth rate until the Ne flow rate equals that of the CH{sub 4}, givingmore » maximum growth rate increases of 70% and 200% for NH{sub 3} and N{sub 2} containing gas mixtures, respectively. At the same time the field emission threshold voltage decreases by a factor of {approximately} 0.5 and 2, respectively. With further increases in Ne flow rate, the film growth rates decrease in both cases, whilst the threshold voltage increases. Micro-combustion measurements show that the N content within the films is proportional to the percentage of the N-containing precursor in the gas phase, but is independent of Ne concentration.« less
  • Trace amounts of H/sub 2/O and limited exposure to air of reaction mixtures of UCl/sub 4/ and 12-crown-4, 15-crown-5, benzo-15-crown-5, 18-crown-6, or dibenzo-18-crown-6 in 1:3 mixtures of CH/sub 3/OH and CH/sub 3/CN resulted in the hydrolysis and oxidation of UCl/sub 4/ to (UO/sub 2/Cl/sub 4/)/sup 2/minus//. In the presence of these crown ethers, it has been possible to isolate intermediate products via crystallization of crown complexes of the (UO/sub 2/Cl/sub 4/)/sup 2/minus// ion, the (UCl/sub 6/)/sup 2/minus// ion, and (UO/sub 2/Cl/sub 2/(OH/sub 2/)/sub 3/). The neutral moiety crystallizes as a hydrogen-bonded crown ether complex; however, crown ether complexation of amore » counterion, either an ammonium ion formed during the oxidation of U(IV) or a Na/sup +/ ion leached from glass reaction vessels, resulted in novel crystalline complexes of the ionic species. ((NH/sub 4/)(15-crown-5)/sub 2/)/sub 2/(UO/sub 2/Cl/sub 4/) /times/ 2CH/sub 3/CN, ((NH/sub 4/)(benzo-15-crown-5)/sub 2/)/sub 2/(UCl/sub 6/) /times/ 4CH/sub 3/CN, and ((NH/sub 4/)(dibenzo-18-crown-6))/sub 2/(UO/sub 2/Cl/sub 4/) /times/ 2CH/sub 3/CN have been structurally characterized by single-crystal X-ray diffraction techniques. The results of all the crystal studies are presented in detail. The ammonium ions interact with the crown ethers via hydrogen-bonding and electrostatic interactions. 15-Crown-5 and benzo-15-crown-5 form 2:1 sandwich cations, allowing no H/sub 4/N/sup +//hor ellipsis/(UO/sub 2/Cl/sub 4/)/sup 2/minus// interaction. The dibenzo-18-crown-6 complexed ammonium ions are 1:1 and form bifurcated hydrogen bonds with the chlorine atoms in the (UO/sub 2/Cl/sub 4/)/sup /minus// anion. The formation of (Na(12-crown-4)/sub 2//sub 2/(UO/sub 2/Cl/sub 4/) /times/ 2OHMe and (UO/sub 2/Cl/sub 2/(OH)/sub 2/)/sub 3/) /times/ 18-crown-6 /times/ H/sub 2/O /times/ OHMe has been confirmed by preliminary single-crystal X-ray diffraction studies.« less