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Neutral gas temperature (Tg) is measured in an industrial high-density inductively coupled etch reactor operating in CF4, SF6, O2, Cl2, or HBr plasmas. Two laser diodes are used to deduce Tg from the Doppler widths of 772.38 and 811.5nm lines absorbed by Ar*(P23) metastable atoms, when a small amount of argon (5%) is added to the gas flow. With the 811.5nm beam passing parallel to the wafer, Tg near the wafer surface is obtained by laser absorption technique. With the 772.38nm beam entering the top of the reactor perpendicular to the wafer surface, the volume averaged temperature is deduced by laser induced fluorescence technique. The volume averaged Tg 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 temp...

This paper deals with the diagnostics of an IPVD process called Highly Ionized Sputter Deposition Process (HISDP) using a high power pulsed magnetron plasma. The HISDP plasma was spatially and temporally characterized in the post-discharge using optical absorption spectroscopy and Langmuir probe time resolved measurements. A circular titanium target was used and the buffer gas was argon. The titanium densities (neutrals and ions) were measured by pulsed resonant absorption spectroscopy technique. The comparison between the experimental results and a simple one-dimensional (1D) model of diffusion shows that the transport of neutral and ionized sputtered atoms is mainly controlled by diffusion for a pressure of 4 Pa (classical for neutrals and ambipolar for ions). Moreover, the limits of the optical absorption spectroscopy technique are investigated at lower pressures.

A two-dimensional time-resolved PIC-MCC simulation was developed for the self-consistent modelling of planar r.f. magnetron reactor. Computation results such as target voltage and sputtering ‘race-track’ are in good agreement with experimental results recorded on our device. New information on the ion and electron transport through the r.f. sheath is provided. We discuss the contribution of the ‘classical’ γ-Townsend secondary emission and of the r.f. volume heating to the discharge maintaining. The present model developed for noble gas (xenon) and metallic target (copper) will be extended to dielectric targets (ceramics).

Multiphoton laser‐induced fluorescence (LIF) and amplified spontaneous emission (ASE) are used to detect ground‐state atoms in oxygen and hydrogen glow discharge plasmas. Experimental results and modeling are analyzed to establish the validity criteria for the use of LIF and ASE as diagnostic probes in the measurements of ground‐state atom concentrations. An absolute calibration of the LIF signals is obtained by vacuum ultraviolet absorption experiments, either on the 130 nm resonant line of the atomic oxygen, or the 125 nm resonant line of the hydrogen atom. Under typical operating conditions of dc glow discharges, that is, for gas pressure between 0.5 and 5.0 Torr and discharge current from 1 to 50 mA, the densities of the atomic species are measured in the range 1013 cm−3–1015 cm−3. Under the same conditions the hydrogen atom temperature varies from (336±43) K to (1580±90) K.

International audience; Broad band UV-visible absorption spectroscopy is widely used to measure the concentration of radicals in reactive plasmas. We extended the applicability of this technique to the VUV (115 nm to 200 nm), the spectral range in which the electronic transitions from the ground state to the Rydberg or pre-dissociated states of many closed shell molecules are located. This gives access to the absolute densities of species which do not, or weakly absorb in the UV/visible range. The technique is demonstrated by measuring the densities of HBr and Br 2 molecules in HBr high-density ICP plasmas. PACs numbers: 52.77.Bn, 52.70.Kz and 33.20.Lg 2 Broad band absorption spectroscopy (BBAS) in the UV-visible region is a widely used technique to measure the absolute concentration of radicals in gaseous media. The application domain of this technique is wide, ranging from the detection of atmospheric gases and pollutants 1 to the measurement of the densities of small polyatomic radicals in reactive plasmas 2, 3, 4, 5. In the past 10 years, the sensitivity of BBAS has been enhanced by two orders of magnitude thanks to the progress in detection system and to recent availability of extremely stable light sources (UV LEDs) 6, 7. This was necessary to probe reactive plasmas, in which the absorbance by radicals is typically smaller than a few 10 -3. However, BBAS is restricted to the detection of radicals which absorbs light in the UV-visible domain, i.e. often small polyatomic radicals. For instance, the detection of larger, closed shell molecules is impossible and relies on the use of more sophisticated laser absorption techniques in the infrared region 8, 9, 10, 11 or on mass spectrometry 12, 13. However, many molecules have Rydberg states or pre-dissociated continuums which absorb in the Vacuum-UV (VUV) spectral range. In etching plasmas, examples of relevant molecules that could be detected in the VUV region includes. Most of these molecules have no transitions accessible in the UV-visible domain, or the transition probability is not large enough for providing measurable absorption rate in low pressure plasmas. Since the electronic transitions from the ground state to the Rydberg states of molecules often have very large probabilities, the VUV absorption spectroscopy is promising to detect those molecules with a high sensitivity and it should be complementary to the typical UV-visible absorption spectroscopy. However, broad band VUV absorption spectroscopy has not yet been used for probing low pressure reactive plasmas. Our experimental set up is shown in Fig.1 and has been described in our previous UV-BBAS publications 14, 15. We are using an industrial, 50 cm diameter etching reactor (Advantage TM G5 silicon etcher from Applied Materials) designed to etch 300 mm diameter 3 wafers. The light source is a high pressure deuterium (D 2) lamp (X2D2 from Hamamatsu) that emits a continuum radiation extending from 100 to 400 nm. A VUV grade parabolic mirror produces a collimated, 1 cm diameter, light beam at 90° from the incident light. This VUV beam crosses the reactor chamber, through two optical ports (with MgF 2 windows) facing each other, at about 5 cm below the reactor roof on which lies the rf coil used to create the plasma. At the exit of the second window, another VUV grade parabolic mirror focuses the VUV beam onto the entrance slit of a 20 cm focal length VUV monochromator (Jobin-Yvon H20-UVL), equipped with a 1200 groove/mm VUV grating. With 40 µm entrance and exit slit widths, the spectral resolution of the system is about 0.2 nm. The light intensity at the exit slit is converted to an electric signal with a solar blind Photomultiplier Tube (PMT) (R8486 from Hamamatsu) backed with a 10 6 V/A amplifier. The choice of reflective optics instead of lenses is mandatory because in the VUV the wavelength dependence of the focal length of lenses is too strong to ensure a good collimation and focussing of the beam all over the 115-200 nm range. To discard the strong plasma induced emission, the intensity of the light from D 2 lamp is modulated at 115 Hz with a tuning fork chopper placed before the first parabolic mirror (see Fig. 1) and the signal from the PMT is processed with a lock-in amplifier 6, whose output is digitalised by an A/D converter and recorded in a computer. The entire optical path (between D 2 lamp / reactor input window and between exit window/PMT) is pumped down to 10 -4 Torr by turbomolecular pumps. To record an absorption spectrum, the wavelength of the monochromator is scanned and the intensity I T (λ) of the transmitted light after having passed through the l = 50 cm plasma is acquired. The absorption spectrum is then deduced from the Beer Lambert law: () () () λ − = λ A exp I I 0 T (1) 4 Where I 0 (λ) is the signal recorded in an empty reactor chamber, A(λ) = Nlσ(λ) is the absorbance, N the density of the absorbing species and σ the absorption cross section. Fig.2 shows the absorption spectra of HBr at different pressures recorded without plasma. HBr is a closed-shell molecule, with (4sσ) 2 (4pσ) 2 (4pπ) 4 molecular orbital electron configuration in the X 1 Σ + ground state 16. According to the Nee et al 17 assignment, the three strongly absorbing peaks of this spectra correspond to the 4pπ →5sσ electron excitation in the Rydberg states C 1 Π (for 137 and 143 nm peaks) and b 3 Π (for 150 nm peak), while the continuum between 154 and 235 nm results from the 4p σ  σ* transition into the dissociative a 3 Π and A 1 Π states (σ* is an antibonding orbital). These authors also give the corresponding cross sections, which can be use to deduce the HBr density from the measured absorbance. However, for a stable gas like HBr, we could directly measure I T /I 0 ratio at different wavelengths as a function of HBr pressure (density) in the chamber. This possibility is of prime importance since as seen in Fig.2, the absorbance of transitions to Rydberg states is strongly saturated even at low HBr densities (A(λ) does not vary linearly with N and is almost saturated for the 143 nm band). It should be emphasised that each of the observed peaks at 137, 143 and 150 nm is in reality composed of many rotational lines, having a Doppler width of about 0.25 pm and of non absorbing regions between these lines. As the width of these lines is much smaller than the 0.2 nm spectral resolution of the monochromator we are using, we can conclude that with the measured absorbance in the range of unity, the absorption on the position of rotational lines is almost total (for more detail see Ref. 4). So, for transitions to the Rydberg states, the medium cannot be considered as optically thin, even at low HBr density. Fortunately, this non linearity is not an issue since most of the molecules accessible in the VUV are stable (i.e. available as commercial gases): it is thus possible to experimentally determine the relation between the measured I T /I 0 and the density, shown in 5 Fig.2. But for the continuum part of the absorption spectrum, this artefact no more exists and the absorbance becomes proportional to the HBr density. Fig.3 shows the absorption spectrum recorded in 5 mTorr total pressure pure HBr plasma at 600 W (without wafer). The absorption spectrum recorded at 1 mTorr HBr gas (no discharge) is also shown in the same figure. Features corresponding to the HBr absorption of these two spectra are very similar, indicating that the density of HBr molecules in the plasma is about 3.10 13 cm -3. Furthermore, new absorption features are seen in the spectrum recorded in the plasma. These New bands are unambiguously attributed to the absorption by Br 2 molecules formed by Br atoms recombination on the reactor walls 18, 19. VUV absorption from Br 2 on a few rotational lines have been observed by the resonance enhanced photo ionization technique and analyzed previously 20 but to our knowledge, its complete VUV absorption spectrum is missing in the literature. To obtain the absorption spectrum of the Br 2 molecule, we subtracted the HBr contribution from the recorded plasma absorption spectrum. The resultant spectrum is shown in the lower part of Fig.3. Beside the absorption spectrum of Br 2 one can distinguish a small contribution from H atoms at 121.6 nm (Lyman α). It is not straightforward to deduce the absolute density of Br 2 from this spectrum since for the same reasons than already mentioned for HBr, the absorption on rotational lines of Br 2 must be saturated and unfortunately it is not permitted to introduce Br 2, which is liquid at room temperature, into the chamber. However, it is possible to produce known amounts of Br 2 molecules by mixing HBr and Cl 2 gases, which react totally together to form HCl and Br 2. 9, 21 So, the absorption spectrum recorded at pressure p in an stochiometric mixtures (2/1) of HBr/Cl 2 gases, will correspond to the one recorded in a mixture of 2/3.p of HCl and 1/3.p of Br 2. Using this procedure, we were able to obtain the wavelength dependent absorption spectra of Br 2 at different pressures. So, the absorbance of Br 2 could be calibrated on an absolute scale 22. It leads to a Br 2 density of 1.45 x 10 13 cm -3 at 600 W rf power (Fig.3). 6 Fig.4 shows the rf power dependence of the HBr and Br 2 densities in a 5 mTorr HBr plasma without etching substrate. With increasing rf power, the electron density and hence the dissociation fraction of HBr molecules increase. Furthermore, since the gas temperature also increases with the electron density 23 and since the pressure is maintained at 5 mTorr, the observed decrease of the HBr density when the rf power increases (Fig.4) can also partially due to the neutral depletion 24. In contrast, when the rf power is increased, the dissociation fraction of HBr increases and more Br atoms are available to recombine on the reactor walls leading to a higher Br 2 density. However, above 200 W, an equilibrium is reached between the dissociation of Br 2 by electron impact and its production by recombination on the reactor walls and the observed decay of Br 2 density must also be due to the neutral depletion by gas heating. In conclusion, VUV absorption spectroscopy is a simple and powerful technique to measure the density of stable molecules in reactive plasmas. Giving access to novel species, it is complementary to the typical absorption spectroscopy in the UV-visible region. Furthermore, owing to the large strength of the transitions in the VUV region, the technique appears to be highly sensitive. It follows that extremely low densities can be measured with a good accuracy. The drawback is that many absorption bands are saturated. However, this is not an issue since the molecules that can be detected are often stable gases, for which the absorbance can be directly calibrated by filling the reactor with known pressure of these gases. The detection limit of the technique can be drastically improved if the PMT detector is replaced by a VUV sensitive Diode-Array or a CCD detector. This will eliminate the nonquantum noise of the sequential scan of the monochromator and would also significantly reduce the data acquisition time. Information we are reporting in this paper are essential for a better understanding of etching processes in HBr-based plasmas, which are widely used in 7 microelectronic industry to etch silicon, and for which information available in the literature are extremely sparse 8.

International audience; Silicon etching in Cl2-based plasmas is an important step for the fabrication of IC circuits but the plasma surface interactions involved in this process remain poorly understood. Based on the developments in plasma and reactor wall diagnostics, this paper reviews the recent progress in the understanding of radicals' interactions with surfaces during silicon etching processes. X-ray photoelectron spectroscopy analysis of the reactor walls shows that during Si etching in Cl2/O2 plasmas, the initial Al2O3 chamber walls are coated with a thin SiOCl layer. Broadband absorption spectroscopy with UV light emitting diodes is used to measure the densities of SiClX radicals (X = 0-2) and Cl2 molecules in steady state plasmas running with the chamber walls coated with different materials. To estimate the surface sticking/recombination probability of these radicals on different surfaces, we have performed time-resolved absorption measurements in the afterglow of pulsed discharges. Our work, in agreement with previous results, shows that the Cl2/Cl density ratio in the discharge is driven mainly by the chemical nature of the chamber walls explaining why process drifts are often observed in Cl2/O2 plasmas. The recombination coefficient of Cl atoms on SiOCl surfaces is about 0.007, while it is about 0.1 on clean walls (AlF3). Based on these results, we discuss the best strategy leading to reproducible process control, the present strategy being a systematic reactor cleaning/conditioning between wafers. The SiOCl layer deposition mechanism is then discussed in detail. The sticking coefficient of SiCl on this surface is near unity, while SiCl2 appears to be weakly reactive toward it. Therefore, SiCl (and SiCl+ ions) are the main vectors of Si deposition on the reactor walls, where their subsequent oxidization by O atoms leads to the formation of a SiOCl deposit. Furthermore, we show that SiCl reaction in the plasma volume with Cl2, through the exchange reaction SiCl + Cl2 → SiCl2 + Cl, is very important for the control of radical densities. Finally, time-resolved measurements of the gas temperature by laser-absorption Doppler spectroscopy show that in the afterglow of pulsed discharges the transport of particles is affected by the convection phenomenon. The very fast electron temperature cooling in the early afterglow generates a pressure gradient in the reactor which induces a rapid gas movement from the cold regions of the reactor toward the reactor center, where the plasma was generated. This leads to an increase in the density of stable molecules in the volume previously occupied by the plasma.

In rare gas/oxygen mixtures, the generation of O2(a∆g) states by microplasmas has been studied experimentally and theoretically. Microplasmas refer to electric discharges created in very small geometries able to operate in DC mode at high pressure without glow to arc transition. A microplasma configuration which has proven to be stable at atmospheric pressure and up to a power density of some 100 kW/cm is the Micro Hollow Cathode Discharge (MHCD) developed by Schoenbach and coworkers. MHCDs are created by applying a voltage between two closely spaced hollow electrodes separated by a dielectric layer. The thickness of the dielectric and the diameter of the hole are both on the order of some 100's microns. These MHCDs can be used as plasma cathodes for generating a diffuse discharge between the MHCD cathode and a third positively-biased electrode placed some distance away. This is the so-called Micro Cathode Sustained Discharge (MCSD) configuration. It is shown in the present paper that these MCSDs can be operated as nonself-sustained discharges with low values of the reduced electric field and of the gas temperature. As a result, these MCSDs can efficiently generate large amounts of singlet delta oxygen. In argon-oxygen mixtures, O2(a∆g) relative yields of 13 % were measured 23 cm downstream in the afterglow of the MCSD discharge, while in helium-oxygen mixtures, O2(a∆g) number densities above 10 cm were achieved at atmospheric pressure for flow rates in the range 5-30 ln/mn. Moreover, it has been demonstrated that MCSDs can be operated in parallel in this non-self-sustained discharge mode. Such arrays of MCSDs offer a new possibility to produce large amounts of O2(a∆g) states, which could give rise to a large spectrum of applications

A high speed electronic switch of discharge current has been used as a diagnostic tool of closed electron drift thrusters. Analysis of transients in discharge current and plasma spectral emissions leads to an evaluation of electron energy and density losses. Low energy excitation processes populating excited states from ion and neutral metastables are evidenced. Measurements of mean electron axial velocity are compared with neutral collision transport across magnetic field. Finally a strong correlation is evidenced between angular distribution of ejected ions and localization of the ionization zone in the thruster channel.

We report experimental results showing that singlet oxygen O2(aΔ1g) can be efficiently produced at atmospheric pressure in a three-electrode microcathode sustained discharge (MCSD) configuration. This configuration consists of a microhollow cathode discharge (MHCD) acting as a plasma cathode to sustain a stable glow discharge between the MHCD and a third planar electrode placed at a distance of 8 mm. Experiments were performed in He/O2/NO mixtures. O2(aΔ1g) number densities higher than 1016 cm−3 were measured in the MCSD afterglow at total flow rates up to 30 ln/mn, resulting in O2(aΔ1g) fluxes above 10 millimole per hour (mmol/h).

In this paper, we report the influence of the various stages of the preionized high power pulsed magnetron discharge on the saturated ion substrate holder current. Our system allows superposition of a preionization low current dc discharge with high voltage pulses applied directly on the magnetron cathode. This system is characterized by a very fast and perfectly reproducible discharge current rise. For a 33?mm copper target, Ar pressure of ~1?Pa, voltage applied in a pulse of ~1?kV, the maximum cathode current of ~40?A is reached in 6??s. The dependence of the saturated ion substrate holder current was analyzed for varying time duration of the high power pulse from 2 up to 8??s by 0.5??s steps. It allows the discrimination of the contribution of elemental temporal intervals to the overall saturated ion substrate holder current. This analysis led to the conclusion that the transport of ballistic ions during the current pulse and in the afterglow is independent of time. We concluded that space charge effects are negligible for both discharge and post-discharge conditions and that electrons act as a neutralizing background. Finally, on the basis of a phenomenological kinetic model for the electron transport, physical explanations of these results are proposed which involve the transverse diffusion of low energy electrons out of the magnetized glow region through electron?ion Coulomb collisions.

Vibrational level population distributions of electrical-discharge-excited nitrogen were measured up to nu =7 by means of a Penning ionisation reaction involving He(23S) metastables. Vibrational level populations of N2(X, nu ) were obtained from the N2+(B, nu 1) level concentrations and the inverted matrix of the Franck-Condon factors. A vibrational temperature range of 2000-8000K was covered with all measured vibrational distributions exhibiting non-Boltzmann, near-Treanor quasi-steady-state behaviour.

A technique is described for the measurement of metastable-state densities by self-absorption in a plasma. The absorption parameter k 0 l is determined from the ratio of the total intensities of two partially self-absorbed lines ending on the level for which one wishes to determine the population. We develop this method for the case of a homogeneous medium for which the emission and absorption lines have Doppler, Lorentz or Voigt profiles. We study the error inherent in this model when the medium is spatially inhomogeneous. We apply this method to the measurement of atomic and ionic metastable concentrations in a highly ionized argon plasma.

A simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O2(a1Δ) and negative ions O — in the positive column of a DC glow discharge is developed. The calculated O and O2(a1Δ) concentrations are compared to previously reported measurements for pressuresp=0.2–2 Torr and discharge currentsI=10–80 mA. The electron density calculated from the continuity equationj=nee vd agrees well with experiment. The rate coefficients for electron impact processes used in the balance equations of O, O2(a1Δ), and O− were taken from the literature as a function of the reduced electric fieldE/N forE/N=40–80 Td. A reasonable agreement is obtained between the model and the experiment with a set of 10 reactions for the production and destruction of the above-mentioned species

The populations of the N2(A 3 Sigma u+, nu =0-5) states in a pure nitrogen glow discharge have been determined from measurements of the absorption of the first positive system bands for gas pressures in the range 0.1-2 Torr and discharge current densities up to about 30 mA cm-2. The observed vibrational distributions are highly non-Boltzmann and an inversion of population between the levels nu =2 and nu =3 was found. The total population in the nu =0-5 levels saturates with increasing current, the saturated population densities ranging from about 3 to 6*1012 cm-3, depending on pressure. An interpretation of the experimental data is given using a kinetic model which includes excitation of individual N2(A, nu ) vibrational levels by electron impact with ground-state molecules and by cascading from the B 3 Pi g to the A state, diffusion to the wall, quenching by nitrogen atoms, metastable-metastable energy pooling, vibration-vibration energy transfer between N2(A) and N2(X) molecules, and collisionally induced transitions between the B 3 Pi g and A 3 Sigma u+ states. The predictions are in good agreement with the measurements. However the observed inversion of population between the nu =2 and nu =3 levels cannot be explained by the above mechanisms. It is suggested that is due to vibrationally dependent quenching.