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Title: Spectroscopic study of gas and surface phase chemistries of CF{sub 4} plasmas in an inductively coupled modified gaseous electronics conference reactor

Abstract

Gas and surface phase chemistries of CF{sub 4} plasma were studied in an inductively coupled modified gaseous electronics conference reference cell, using in situ Fourier transform infrared spectroscopy enhanced by a multipass White cell and in situ spectroscopic ellipsometry. The self-bias dc voltage, densities of gaseous species, fluorocarbon film thickness on Si substrate, as well as etch rates of SiO{sub 2} and Si were measured during plasma processing as functions of the pressure, CF{sub 4} gas flow rate, rf source power, platen bias power, and source-platen gap. The gaseous molecules and radicals monitored included CF{sub 4}, CF{sub 3}, CF{sub 2}, SiF{sub 4}, and COF{sub 2}, among which CF{sub 4} and SiF{sub 4} were found to be the two dominant species, combining for about 80% of the total concentration. The density ratio of SiF{sub 4} and COF{sub 2} was about 2:1 with no bias on the substrate and increased up to {approx}8:1 when Si substrate etching took place. Specifically, as the Si etch rate increased, the COF{sub 2} density dropped, likely due to suppressed etching of the quartz source window, while the density of SiF{sub 4} increased. Comparisons between the gas phase data and etch rate results of Si and SiO{submore » 2} indicate that the gas phase chemistry is strongly influenced by surface reactions on the substrate, wall, and quartz source window. The thickness of fluorocarbon reaction layer on Si substrate is mainly determined by densities of fluorocarbon radicals and fluorine atoms in the bulk plasma as well as the self-bias voltage on the substrate, and a thicker film is usually associated with a lower etch rate.« less

Authors:
; ; ;  [1]
  1. Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas 75083 (United States)
Publication Date:
OSTI Identifier:
20776939
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: 24; Journal Issue: 1; Other Information: DOI: 10.1116/1.2138718; (c) 2006 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CARBON TETRAFLUORIDE; CHEMISTRY; COBALT FLUORIDES; DENSITY; ETCHING; FILMS; FLUORINE; FOURIER TRANSFORM SPECTROMETERS; FOURIER TRANSFORMATION; INFRARED SPECTRA; PLASMA; PLASMA DENSITY; QUARTZ; SEMICONDUCTOR MATERIALS; SILICA; SILICON; SILICON OXIDES; SUBSTRATES; SURFACES

Citation Formats

Zhou Baosuo, Joseph, Eric A., Overzet, Lawrence J., and Goeckner, Matthew J. Spectroscopic study of gas and surface phase chemistries of CF{sub 4} plasmas in an inductively coupled modified gaseous electronics conference reactor. United States: N. p., 2006. Web. doi:10.1116/1.2138718.
Zhou Baosuo, Joseph, Eric A., Overzet, Lawrence J., & Goeckner, Matthew J. Spectroscopic study of gas and surface phase chemistries of CF{sub 4} plasmas in an inductively coupled modified gaseous electronics conference reactor. United States. doi:10.1116/1.2138718.
Zhou Baosuo, Joseph, Eric A., Overzet, Lawrence J., and Goeckner, Matthew J. Sun . "Spectroscopic study of gas and surface phase chemistries of CF{sub 4} plasmas in an inductively coupled modified gaseous electronics conference reactor". United States. doi:10.1116/1.2138718.
@article{osti_20776939,
title = {Spectroscopic study of gas and surface phase chemistries of CF{sub 4} plasmas in an inductively coupled modified gaseous electronics conference reactor},
author = {Zhou Baosuo and Joseph, Eric A. and Overzet, Lawrence J. and Goeckner, Matthew J.},
abstractNote = {Gas and surface phase chemistries of CF{sub 4} plasma were studied in an inductively coupled modified gaseous electronics conference reference cell, using in situ Fourier transform infrared spectroscopy enhanced by a multipass White cell and in situ spectroscopic ellipsometry. The self-bias dc voltage, densities of gaseous species, fluorocarbon film thickness on Si substrate, as well as etch rates of SiO{sub 2} and Si were measured during plasma processing as functions of the pressure, CF{sub 4} gas flow rate, rf source power, platen bias power, and source-platen gap. The gaseous molecules and radicals monitored included CF{sub 4}, CF{sub 3}, CF{sub 2}, SiF{sub 4}, and COF{sub 2}, among which CF{sub 4} and SiF{sub 4} were found to be the two dominant species, combining for about 80% of the total concentration. The density ratio of SiF{sub 4} and COF{sub 2} was about 2:1 with no bias on the substrate and increased up to {approx}8:1 when Si substrate etching took place. Specifically, as the Si etch rate increased, the COF{sub 2} density dropped, likely due to suppressed etching of the quartz source window, while the density of SiF{sub 4} increased. Comparisons between the gas phase data and etch rate results of Si and SiO{sub 2} indicate that the gas phase chemistry is strongly influenced by surface reactions on the substrate, wall, and quartz source window. The thickness of fluorocarbon reaction layer on Si substrate is mainly determined by densities of fluorocarbon radicals and fluorine atoms in the bulk plasma as well as the self-bias voltage on the substrate, and a thicker film is usually associated with a lower etch rate.},
doi = {10.1116/1.2138718},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 1,
volume = 24,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • The effect of wall temperature, from 50 to 200 deg. C, on gas phase chemistry and substrate etching rates has been studied in inductively coupled CF{sub 4} plasma under two distinctive initial wall conditions, namely 'clean' and 'seasoned'. During plasma etching, we found that the gas phase chemistry exhibits a weak dependence on the initial wall cleanliness when the wall is either cold (50 deg. C) or hot (200 deg. C). In the mid-temperature range, the wall cleanliness can strongly affect gas phase chemistry. The study of temperature dependence of the fluorocarbon film deposition on the substrate indicates that ion-assistedmore » incorporation, direct ion incorporation and ion-assisted desorption are the major factors determining film growth and removal. Ion-assisted incorporation and desorption are surface-temperature-dependent, while direct ion incorporation is independent of the surface temperature.« less
  • Neutral gas temperature (T{sub g}) is measured in an industrial high-density inductively coupled etch reactor operating in CF{sub 4}, SF{sub 6}, O{sub 2}, Cl{sub 2}, or HBr plasmas. Two laser diodes are used to deduce T{sub g} from the Doppler widths of 772.38 and 811.5 nm lines absorbed by Ar*({sup 3}P{sub 2}) metastable atoms, when a small amount of argon (5%) is added to the gas flow. With the 811.5 nm beam passing parallel to the wafer, T{sub g} near the wafer surface is obtained by laser absorption technique. With the 772.38 nm beam entering the top of the reactormore » perpendicular to the wafer surface, the volume averaged temperature is deduced by laser induced fluorescence technique. The volume averaged T{sub g} increases with radio frequency power and with pressure, although the temperature near the walls is only weakly dependent on gas pressure. The main effect of increasing the pressure is an enhancement of the temperature gradient between the discharge center and the wall boundary. Due to the thermal accommodation, the authors always observe a significant temperature jump between the surface and the gas in its vicinity. This gap is typically about 200 K. Gas temperatures for a wide range of pressure and rf powers are reported. These data will be useful to validate and improve numerical models of high-density reactive plasmas.« less
  • Utilizing infrared diode-laser absorption spectroscopy (IRDLAS) and UV-Visible absorption spectroscopy (UV-Vis), we show that it is possible to make a near complete mass balance of etch reactants and products in a GEC inductively coupled fluorocarbon discharge while actively etching SiO{sub 2} substrates. Langmuir probe measurements were performed to measure the total ion current density. C{sub 2}F{sub 4} and CF{sub 2} are shown to be the main dissociation products in a C{sub 4}F{sub 8} plasma discharge. The C{sub 2}F{sub 4} concentration decreases as the SiO{sub 2} etching rate increases, along with CF{sub 2} and CF radicals, suggesting a role in themore » SiO{sub 2} etching process. The addition of Ar to the C{sub 4}F{sub 8} discharge increased the ion flux at the wafer surface, and the consumption rate of C{sub 2}F{sub 4} relative to CF{sub 2}. The increased ion flux enhanced the SiO{sub 2} etching rate, until at a very high degree of Ar dilution of C{sub 4}F{sub 8}/Ar the etching rate became neutral limited. We also monitored SiF{sub 2} using UV-Vis absorption and CO by IRDLAS. In our work we found SiF{sub 2} and CO to be the prevalent Si and C gas phase etch products for the SiO{sub 2} etching process.« less
  • Inductively coupled plasma (ICP) etching of GaN, AlN, InN, InGaN, and InAlN was investigated in CH{sub 4}/H{sub 2}/Ar and Ch{sub 4}/H{sub 2}/N{sub 2} plasmas as a function of dc bias, ICP power, and pressure. The etch rates were generally quite low, as is common for III-nitrides in CH{sub 4}-based chemistries. In CH{sub 4}/H{sub 2}/Ar plasmas, the etch rates increased with increasing dc bias. At low radio frequency power (150 W), the etch rates increased with increasing ICP power, while at 350 W radio frequency power, a peak was found between 500 and 750 W ICP power. The dc bias wasmore » found to increase with increasing pressure. The etch rates in the CH{sub 4}/H{sub 2}/N{sub 2} chemistry were significantly lower, with a peak at 500 W ICP power. The etched surfaces were smooth, while selectivities of etch were {le} 6 for InN over GaN, AlN, InGaN, and InAlN under all conditions.« less
  • Highly selective etching of SiO{sub 2} over Si is central to the manufacture of ultralarge scale integration devices; the process is generally one of reactive ion etching using polymerizing fluorocarbon chemistry. A number of species including electrons, ions, and radicals are generated by reactions in the gas phase and on the surface in the plasma process. A large number of highly reactive fluorine atoms, fluorocarbon radicals, and ions interact with the substrate and produce etch products. These etch products, primarily SiF{sub 4} and SiF{sub 2}, diffuse back into the bulk plasma where they are dissociated and ionized by interactions withmore » electrons, and the resultant products are transported and redeposited onto the substrate and/or wall surface. That is, the plasma structure may differ depending on whether the Si (or SiO{sub 2}) surface has been exposed to etching or not. Hence, it is essential to investigate the spatiotemporal characteristics of the plasma structure during etching. In this study, measurements of plasma structure during Si or SiO{sub 2} etching in CF{sub 4}/Ar radio-frequency inductively coupled plasma (rf-ICP) were performed using computerized tomography of optical emission spectroscopy to investigate plasma-surface interactions. We focused on the characteristics of etch products, their daughter products, and the etchant in the gas phase during Si and SiO{sub 2} etching in CF{sub 4}/Ar rf-ICP and the disturbance of the plasma structure at high amplitudes of LF bias.« less