Nicolas Bulcourt

Laboratory of Plasma Physics, Paliseau, Île-de-France, France

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Publications (7)3.12 Total impact

  • Nicolas Bulcourt, Jean-Paul Booth, Garrett Curley
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    ABSTRACT: The radical CF2 was detected using broad-band UV absorption spectroscopy in a dual RF frequency (2 and 27 MHz) capacitive discharge in Ar/C_4F_8/O_2. The objective was to obtain the radial and axial profiles of the CF2 density and temperature for different discharge conditions. Absorption spectra were taken at different radial chords: the absorption spectra at different radii were then obtained by Abel inversion. The densities and temperatures were then obtained by comparing the experimental CF2 spectra to spectrum simulations. These simulations used recently calculated values of the Franck-Condon factors and rotational constants calculated [1]. The results showed that the CF2 rotational and vibrational temperatures at the center of the reactor are high (up to 500 K and 1000 K respectively). Radical production and gas heating mechanisms will be discussed. We acknowledge financial support from the Lam foundation. [1] N. Bulcourt, J.-P. Booth, E. A. Hudson, J. Luque, D. K. W. Mok, E. P. Lee, F.-T. Chau, J. M. Dyke . Chem. Phys. 120, 9499 (2004).
    09/2004;
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    ABSTRACT: Dual-frequency capacitive plasmas in Ar/C_4F_8/O2 gas mixtures are widely used for etching dielectric materials in integrated circuit manufacture. C_4F8 is reported to be a highly electronegative gas [1] and therefore one would expect that negative ions could play an important role in this type of plasma. The presence of negative ions will modify the positive ion velocity at the sheath edge and therefore the positive ion flux arriving at a surface. We have attempted to directly measure the negative fluorine ion F^- density using broadband UV absorption spectroscopy, setting an upper limit on their density of 5x10^11cm-3. These measurements were complimented by measurements of the positive ion flux and the electron density. In conjunction with analytical models, these methods provide another avenue to determine the negative ion fraction. We acknowledge financial support from the Lam Foundation. [1] Kono et al, Jpn. J. Appl. Phys. (39) 2000, 1365-1368
    09/2004;
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    ABSTRACT: Broadband ultraviolet absorption spectroscopy has been used to determine CF(2) densities in a plasma etch reactor used for industrial wafer processing, using the CF(2) A (1)B(1)<--X (1)A(1) absorption spectrum. Attempts to fit the experimental spectra using previously published Franck-Condon factors gave poor results, and values for the higher vibrational levels of the A state [(0,v(2),0), with v(2) (')>6] from the ground state were missing; hence new values were calculated. These were computed for transitions between low-lying vibrational levels of CF(2) X (1)A(1) to vibrational levels of CF(2) A (1)B(1) (v(1) ('),v(2) ('),0) up to high values of the vibrational quantum numbers using high level ab initio calculations combined with an anharmonic Franck Condon factor method. The Franck Condon factors were used to determine the absorption cross sections of CF(2) at selected wavelengths, which in turn were used to calculate number densities from the experimental spectra. Number densities of CF(2) have been determined in different regions of the plasma, including the center of the plasma and outside the plasma volume, and CF(2) rotational temperatures and vibrational energy distributions were estimated. For absorption spectra obtained outside the confined plasma volume, the CF(2) density was determined as (0.39+/-0.08)x10(13) molecule cm(-3) and the vibrational and rotational temperatures were determined as 303 and 350 K, respectively. In the center of the plasma reactor, the CF(2) density is estimated as (3.0+/-0.6)x10(13) molecules cm(-3) with T(rot) approximately 500 K. The fitted vibrational distribution in the CF(2) ground state corresponds to two Boltzmann distributions with T(vib) approximately 300 and T(vib) approximately 1000 K, indicating that CF(2) molecules are initially produced highly vibrationally excited, but are partially relaxed in the plasma by collision.
    The Journal of Chemical Physics 06/2004; 120(20):9499-508. · 3.12 Impact Factor
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    ABSTRACT: Broad band UV absorption spectroscopy of CF2 was performed in an industrial Ar/C_4F_8/O2 dual RF frequency (2 and 27 MHz) capacitive discharge (Lam Research Corp.). The objective was to obtain the radial profiles of the CF2 density and temperature. To achieve this experimental and simulated spectra were compared. The spectra were simulated using Franck-Condon factors and rotational constants calculated theoretically using an improved potential energy function (PEF) of the A state and a published PEF for the ground state. CF2 spectra for beam paths including and excluding the confined plasma volume were compared. Results showed that the gas temperature at the center of the reactor is high (roughly 550 K) and decreases towards the wall of the chamber. Radical production and gas heating mechanisms will be discussed.
    10/2003;
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    ABSTRACT: Laser Induced fluorescence (LIF) was used to determine axial profiles of CF and CF2 density and gas temperature in an inductively-coupled plasma in CF4 at 33 mTorr. The gas temperature reaches 800 K in the reactor centre, causing considerable gas rarefaction at constant pressure. This most be taken into account when calculating radical fluxes due to diffusion. The steady-state CF and CF2 density profiles are hollow, showing that the net radical fluxes are away from the reactor surfaces (where they are produced) towards the reactor centre (where they are destroyed). In the post-discharge the gas cools in about a millisecond. The CF density drops rapidly due to gas-phase reactions, probably with molecular fluorine. The CF2 density initially increases (by a factor of about 3) for the first millisecond, before decaying slowly. This increase is due to continued surface production of CF2 in the afterglow, combined with the disappearance of the rapid gas-phase CF2 loss process. Numerical simulations using the FEMLAB package were used to understand the diffusive and convective radical transport in the afterglow.
    10/2003;
  • Jean-Paul Booth, Nicolas Bulcourt, Jacques Jolly
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    ABSTRACT: Capacitively-coupled plasmas in gas mixtures of the type Ar/C_4F_8/O2 (90 % Ar) have become the standard in the microelectronics industry for the etching of contact holes in SiO2 thin films, displacing inductively-coupled sources. However, small changes in the gas composition can have dramatic effects on the process results (narrow "process window"). We have investigated the ion mass and energy distributions in a 27 MHz parallel plate system using a quadrupole mass spectrometer with energy analyser. The dominant ions include Ar^+, C_2F_5^+, C_3F_5^+, CF_3^+, C_4F_7^+, COF^+ and CF^+. The Ar^+ energy distribution functions are strongly degraded to low energies due to charge exchange collisions in the sheath. Increasing RF power increases the degree of fragmentation, leading to more low-mass molecular ions. The effect of replacing 50 % of the Ar with Xe was investigated. The principal effect is to replace the majority Ar^+ ion by Xe^+. The Xe^+ energy distribution functions are less degraded to low energies than is the case for Ar^+.
    10/2002;
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    N Bulcourt, J P Booth, G Curley
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    ABSTRACT: Measurements are presented of CF and CF 2 radical density and temperature axial profiles, obtained from the UV broad-band spectroscopy of the CF B-X bands and the CF 2 A-X bands in an Ar/C 4 F 8 /O 2 dual-frequency capacitive discharge (DFC). The gas translational temperature increases towards the substrate on the powered electrode. High vibrational temperatures are observed at the reactor centre. The CF 2 number densities increase towards the (colder) reactor roof, but the mole-fraction profiles are uniform. The CF density profiles show more complex behaviour.