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Title: Influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas

Abstract

Langlois et al. [Appl. Phys. Lett. 87, 131503 (2005)] have demonstrated that the etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas decreases as the concentration fraction of molecular ions in the plasma increases. Introducing the concept of effective mass for both ions and SrTiO{sub 3}, these experimental results have quantitatively been explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by nonreactive monoatomic ions. This model has, however, ignored the dissociation of molecular ions occurring as these particles impact the material surface. In the present article, the influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas is reexamined to the light of this consideration. A rate model accounting for the dissociation of the various molecular ions is proposed and validated using experimental data. It is found that even though a specific ion species may not be the most important charge carrier in the plasma, its contribution to the plasma etching dynamics may still be the most significant.

Authors:
; ; ; ;  [1];  [2]
  1. Departement de Physique, Universite de Montreal, Montreal, Quebec H3C 3J7 (Canada)
  2. (Canada)
Publication Date:
OSTI Identifier:
20979363
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: 3; Other Information: DOI: 10.1116/1.2713410; (c) 2007 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ARGON COMPOUNDS; CATIONS; EFFECTIVE MASS; ETCHING; MOLECULAR IONS; PLASMA; SPUTTERING; STRONTIUM TITANATES; SULFUR FLUORIDES; THIN FILMS

Citation Formats

Stafford, L., Langlois, O., Margot, J., Gaidi, M., Chaker, M., and INRS-Energie, Materiaux et Telecommunications, Varennes, Quebec J3X 1S2. Influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas. United States: N. p., 2007. Web. doi:10.1116/1.2713410.
Stafford, L., Langlois, O., Margot, J., Gaidi, M., Chaker, M., & INRS-Energie, Materiaux et Telecommunications, Varennes, Quebec J3X 1S2. Influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas. United States. doi:10.1116/1.2713410.
Stafford, L., Langlois, O., Margot, J., Gaidi, M., Chaker, M., and INRS-Energie, Materiaux et Telecommunications, Varennes, Quebec J3X 1S2. Tue . "Influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas". United States. doi:10.1116/1.2713410.
@article{osti_20979363,
title = {Influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas},
author = {Stafford, L. and Langlois, O. and Margot, J. and Gaidi, M. and Chaker, M. and INRS-Energie, Materiaux et Telecommunications, Varennes, Quebec J3X 1S2},
abstractNote = {Langlois et al. [Appl. Phys. Lett. 87, 131503 (2005)] have demonstrated that the etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas decreases as the concentration fraction of molecular ions in the plasma increases. Introducing the concept of effective mass for both ions and SrTiO{sub 3}, these experimental results have quantitatively been explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by nonreactive monoatomic ions. This model has, however, ignored the dissociation of molecular ions occurring as these particles impact the material surface. In the present article, the influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas is reexamined to the light of this consideration. A rate model accounting for the dissociation of the various molecular ions is proposed and validated using experimental data. It is found that even though a specific ion species may not be the most important charge carrier in the plasma, its contribution to the plasma etching dynamics may still be the most significant.},
doi = {10.1116/1.2713410},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 3,
volume = 25,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • The influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO{sub 3} films in Ar/SF{sub 6} plasmas is investigated using a parametric approach. The etch yield is found to decrease as the concentration fraction of molecular ions increases. Introducing the concept of effective mass for both ions and SrTiO{sub 3}, these experimental results are quantitatively explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by noble monoatomic ions.
  • Recently, Stafford et al. [Appl. Phys. Lett. 87, 071502 (2005)] have shown that in contrast to the etch yield on a saturated surface, the ion-assisted chemical etch rate cannot universally be modeled by a simple square-root energy dependence. This results from the surface coverage by reactive neutral species being also a function of the ion energy. In this work, we further point out that depending on the plasma-material combination, the etch rate can exhibit two regimes that are characterized by different dependences on the ion energy. While these results are inconsistent with currently available models, we show that they canmore » be interpreted by taking into account ion mixing effects on the desorption rate of volatile reaction products involved in the model of Stafford et al. Application of this rate model to the etching of Si, SiO{sub 2}, HfO{sub 2}, and ZrO{sub 2} in chlorine and fluorine plasma chemistries provides an excellent description of the simultaneous dependence of the etch rate on ion energy and on ion and reactive neutral fluxes.« less
  • The measurement of the mobility of SF{sub 6}{sup -} in the mixtures SF{sub 6}-Ar and SF{sub 6}-Xe is reported over the density-reduced electric field strength E/N 1-180 Td (1 Townsend=10{sup -17} V cm{sup 2}), from a time-resolved pulsed Townsend technique. Simultaneously, the mobility of SF{sub 6}{sup -} in the same binary mixtures has been calculated from a set of collision cross sections for SF{sub 6}{sup -}-Ar, SF{sub 6}{sup -}-Xe, and SF{sub 6}{sup -}-SF{sub 6} using a Monte Carlo simulation procedure for ion transport. The good agreement between measured and calculated mobilities in these gas mixtures has led us to concludemore » that the validation of our cross section sets is confirmed. The elastic collision cross section, a predominant process for ion energies lower than about 10 eV, was determined from a semiclassical JWKB approximation using a rigid core potential model for the ion-neutral systems under consideration. This elastic cross section was then added to several other inelastic collision cross sections found in the literature for ion conversion, electron detachment of SF{sub 6}{sup -} and charge transfer. Moreover, the calculations of the mobility and the ratios of the transverse and longitudinal diffusion coefficients to the mobility were extended into a much wider E/N range from 1 to 4000 Td. Additionally, we have also calculated the energy distribution functions and the reaction coefficients for ion conversion and electron detachment. Finally, we have shown that the range of validity for the calculation of the mobility in gas mixtures from Blanc's law is only valid for the low E/N region, where the interaction is dominated by elastic collisions and the ion distribution function remains essentially Maxwellian.« less
  • We have investigated the growth of BaTiO{sub 3} thin films deposited on pure and 1% Nb-doped SrTiO{sub 3}(001) single crystals using atomic oxygen assisted molecular beam epitaxy and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO{sub 3} layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {approx}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers.more » We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO{sub 3} layers, especially in view of their integration in devices.« less
  • While plasmas using mixtures of SF{sub 6}, C{sub 4}F{sub 8}, and Ar are widely used in deep silicon etching, very few studies have linked the discharge parameters to etching results. The authors form such linkages in this report. The authors measured the optical emission intensities of lines from Ar, F, S, SF{sub x}, CF{sub 2}, C{sub 2}, C{sub 3}, and CS as a function of the percentage C{sub 4}F{sub 8} in the gas flow, the total gas flow rate, and the bias power. In addition, the ion current density and electron temperature were measured using a floating Langmuir probe. Formore » comparison, trenches were etched of various widths and the trench profiles (etch depth, undercut) were measured. The addition of C{sub 4}F{sub 8} to an SF{sub 6}/Ar plasma acts to reduce the availability of F as well as increase the deposition of passivation film. Sulfur combines with carbon in the plasma efficiently to create a large optical emission of CS and suppress optical emissions from C{sub 2} and C{sub 3}. At low fractional flows of C{sub 4}F{sub 8}, the etch process appears to be controlled by the ion flux more so than by the F density. At large C{sub 4}F{sub 8} fractional flows, the etch process appears to be controlled more by the F density than by the ion flux or deposition rate of passivation film. CF{sub 2} and C{sub 2} do not appear to cause deposition from the plasma, but CS and other carbon containing molecules as well as ions do.« less